• Brasier

Linse, K M Mackenzie

A Taylor

Wiklund, H & Griffiths

) Benthic

Grant, S.M H Griffiths

• Moreau

Downey, R., & Jossart Q Asteroid

Oral presentations

Je tiens ensuite à remercier Bruno Danis, mon promoteur, qui a cru et s'est investi dans la mise en place de ce projet de thèse. Tu m'auras laissé beaucoup de liberté et toujours soutenu pour me permettre de participer aux missions de terrain et conférences à travers le monde.

C'est, je crois, l'un des plaisirs de tout scientifique que d'avoir la chance de partir en expéditions, et lorsque celles-ci se déroulent en Antarctique ou Terre de Feu, ces souvenirs sont d'autant plus mémorables.

Je souhaite remercier Thomas Saucède, mon directeur de thèse à l'Université Bourgogne Franche-Comté de Dijon. Tu auras su me pousser, dans le calme et la sagesse qui te caractérisent, à toujours aller plus loin dans la réflexion et l'intégration de nouvelles méthodes pour aborder mon sujet tout en développant une vue d'ensemble, perfectionnant ainsi le résultat final de la thèse.

J'ai une pensée particulière pour les personnes qui ont pris part à la genèse de mon cursus et ma carrière. Merci à Marc Eléaume et Nadia Améziane de m'avoir proposé mon premier stage en relation avec l'Océan Austral et d'avoir contribué à faire grandir ma passion pour les hautes latitudes. A massive "thank you" to Katrin Linse. You gave me the opportunity to join the British Antarctic Survey and to take part in my first cruise in Antarctica. It is during this scientific voyage that I met and bound with great scientists and friends who were and still are inspirations for my career. Thank you Cheps, Bec, Jack, Grace and Nina for always being here I needed it, whether for scientific or personal advices, you are part of my life as my Cambridge family and much more. Thank you, Huw, for your support, putting me in contact with Bruno, inviting me around the South Orkney and always pushing to help early carrier scientists to be part of the community, in the field or during conferences. Many thanks to Dave for including me in his team, whether it is about cycling or science, you are a model of wisdom and it is always pleasant to learn by your side. Finally, a special thanks to Oli and Rachel with whom I shared great moments before and during the PhD and hopefully many more are to come. Les soutiens viennent aussi évidemment de l'entourage extra-professionnel et sur ce point je souhaite remercier mes amis du handball avec lesquels j'ai partagé énormément de bons moments qui m'auront permis de mettre de côté la science et de donner de l'importance à d'autres choses. Un grand merci Simon, Quentin, Philipp, Melissa, Lena, Mélanie, Ana, Natalita et tous les autres.

Je voudrais aussi remercier les membres de mon jury d'évaluation, Thierry Rigaud et Anton

Van De Putte pour leur relecture ainsi que les conseils apportés sur mon manuscrit de thèse.

Je remercie également ma famille qui m'a toujours soutenu dans mes projets et aidé à les mener à bien même dans les moments difficiles. En me laissant tout au long de ma vie la liberté de faire ce qui me plaisait j'ai pu réaliser mes rêves et atteindre les objectifs que je voulais. Merci maman, papa, Guillaume et Lise.

Merci aussi à mes amis en Bretagne, je n'ai malheureusement plus énormément d'occasion de venir vous rendre visite. Je sais cependant que je peux toujours compter sur vous quand je rentre dans notre beau pays. Merci Alix, Christophe, Valentin et Vincent.

J'ai une pensée particulière pour Margot, tu as été présente et as su me soutenir, dans les moments compliqués, avant et pendant la mise en place de ce projet sans jamais économiser ton énergie pour me conforter dans mes choix. Merci pour tout.

Merci Charlène d'y avoir partagé ton inépOUIsable énergie et de m'y avoir supporté dans le bureau. Merci pour ton aide, notamment sur « R » et lors de nos longues conversations sur la modélo et la génétique. Il était bon d'avoir une compatriote à mes côtés dans le labo.

Sarah, je te remercie énormément pour tout ce que tu m'as apporté lors des baisses de moral mais aussi lorsque tout allait au mieux. Tu m'as fait découvrir beaucoup de belles choses à Bruxelles et en Belgique. C'est en partie grâce à toi si j'ai réussi et je t'en suis très reconnaissant.

Et enfin peut-être le meilleur, mais en tous les cas le plus touffu pour la fin. Je parle, BIEN SUR, de mon bel ami le Belge, docteur Quentin Jossart. Toujours calme et réfléchi, c'est pas Zizou mais c'est un vrai atout de t'avoir et de t'avoir eu dans le bureau et en dehors au cours de toutes ces années. Toutes ces heures à discuter, jouer au foot, perdre notre temps m'auront beaucoup apporté. Je n'oublie évidemment pas de faire un petit clin d'oeil à sa concubine Sophie qui a supporté toutes nos idioties en gardant le sourire. Merci à vous.

Scientific communications during the PhD Publications

• PhD thesis research

• Moreau, C., Jossart, Q., Danis, B., Eléaume, M., Christiansen, H., Guillaumot, C., & Saucède, T. The atypical and overlooked diversity of Southern Ocean sea stars (Asteroidea). (Submitted. Zoological Journal of the Linnean Society) → Chapter 3

• Brasier, M.J.*, Griffiths, H., Grant, S.M., Trathan, P.N., Allcock, L., Ashford, O., Blagbrough, H., Brandt, A., Danis, B., Downey, R., Eléaume, Enderlein, P., M., Ghiglione, C., Hogg, O., Linse, K., Mackenzie, M., Moreau, C., Robinson, L.F., Rodriguez, E., Spiridonov, V., Tate, A., Taylor, M., Waller, C., & Wiklund, H. SO-AntEco: Contributing information and scientific advice to the CCAMLR South Orkney Islands MPA review. Scientific Committee on Antarctic Research, XII Biology Symposium, Leuven, Belgium, 07/2017.

• Schiaparelli, S.*, Chiara, A.M., Cecchetto, M., Danis, B., Fassio, G., Guzzi, A., Jossart, Q., Modica, M.V., Moreau, C., & Oliverio, M. Inventory completeness and accuracy of taxonomic determination: outcomes of a large scale barcoding effort of echinoderms in Terra Nova Bay (Antarctica, Ross Sea). Scientific Committee on Antarctic Research, XII Biology Symposium, Leuven, Belgium, 07/2017.

. 38

Figure 6 A sketch of the Antarctic Circumpolar Current system showing the zonal flow and the meridional overturning circulation and water masses. Antarctica is at the left side. The east-west section displays the isopycnal (same density) and sea surface tilts in relation to submarine ridges, which are necessary to sustain the bottom form stress signatures (see Olbers et al. 2004). The curly arrows at the surface indicate the buoyancy flux; the arrows attached to the isopycnals represent turbulent mixing. An upper cell is formed primarily by northward Ekman transport (horizontal transport of superficial water layers through wind friction) beneath the strong westerly winds and southward transport in the Upper Circumpolar Deep Water (UCDW) layer. The lower cell is driven primarily by formation of dense AABW near the Antarctic continent and inflowing Lower Circumpolar Deep Water (UCDW or NADW). Seven key events through the Cenozoic era are superimposed on the deep-sea palaeotemperature curve developed by [START_REF] Zachos | An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics[END_REF][START_REF] Hansen | Climate sensitivity, sea level and atmospheric carbon dioxide[END_REF] It should be noted that shelf-depth palaeotemperatures do not necessarily track those of the deep-sea precisely. The trajectory of Antarctic taxonomic diversity through the Cenozoic is still imperfectly known, but it may not bear any close similarity to either the shallow-or deep-sea palaeotemperature curves. Symbols: ACC, Antarctic Circumpolar Current, K, Cretaceous, Pl., Pliocene, P., Pleistocene . Ocean as we know it today. Within these ~175 Myr, the supercontinent partitioned into seven distinct continental masses: Antarctica, Australia, New Zealand, India, Madagascar (East) and Africa, South America (West) [START_REF] Knox | Biology of the Southern Ocean[END_REF]. Starting with the initial rifting between West and East Gondwana around 175 Ma, it was not until the Early Cretaceous (130 Ma) that the separation was complete, resulting in the formation of the Weddell Sea and initiating the physical isolation of East Gondwana at high latitudes (Figure 1; [START_REF] Crame | An evolutionary perspective on marine faunal connections between southernmost South America and Antarctica[END_REF]. Around this period, during the Early Cretaceous, rapid northward motion of India started together with the drifting and isolation between Africa and South America [START_REF] Crame | An evolutionary perspective on marine faunal connections between southernmost South America and Antarctica[END_REF][START_REF] Mcloughlin | The breakup history of Gondwana and its impact on pre-Cenozoic floristic provincialism[END_REF].

At the same time Antarctica drifted to its contemporary location and shallow seaways started to emerge between Antarctica and Australia [START_REF] Lawver | Opening of Drake Passage and its impact on Cenozoic ocean circulation[END_REF][START_REF] Mcloughlin | The breakup history of Gondwana and its impact on pre-Cenozoic floristic provincialism[END_REF].

During the Late Cretaceous (80 Ma) New Zealand separated from the Antarctic continent leaving only Tasmania in the East and South America in the West blocking deep water circulation until the end of the Paleogene, ~25 Ma [START_REF] Crame | An evolutionary perspective on marine faunal connections between southernmost South America and Antarctica[END_REF]. The Cenozoic was a period of dramatic changes with the opening of two key deep ocean gateways: one between Tasmania and Antarctica and the other between South America and Antarctica [START_REF] Crame | An evolutionary perspective on marine faunal connections between southernmost South America and Antarctica[END_REF].

The former started 64 Ma leading to a complete separation between continental masses by the beginning of the Eocene 50 Ma [START_REF] Crame | An evolutionary perspective on marine faunal connections between southernmost South America and Antarctica[END_REF] while the latter lead to the disruption of the Weddellian Isthmus and opening of Drake Passage [START_REF] Reguero | Final Gondwana breakup: the Paleogene South American native ungulates and the demise of the South America-Antarctica land connection[END_REF], believed to have occurred around 40 Ma with some debate about the accurate dating of the different geologic phases that succeeded between 6 and 41 Ma [START_REF] Thatje | Effects of capability for dispersal on the evolution of diversity in Antarctic benthos[END_REF][START_REF] Scher | Circulation in the Southern Ocean during the Paleogene inferred from neodymium isotopes[END_REF][START_REF] Lyle | Late Oligocene initiation of the Antarctic circumpolar current: evidence from the South Pacific[END_REF][START_REF] Barker | Origin, signature and palaeoclimatic influence of the Antarctic Circumpolar Current[END_REF]. These last two events, and particularly the opening of the Drake Passage between Antarctica and South America allowed the circulation of deep circum-Antarctic waters and onset of the Antarctic Circumpolar Current. These current systems are the main driving forces of the physical and thermal isolation of the Southern Ocean from other water masses (Lagabrielle et al. 2009[START_REF] Thatje | Effects of capability for dispersal on the evolution of diversity in Antarctic benthos[END_REF][START_REF] Reguero | Final Gondwana breakup: the Paleogene South American native ungulates and the demise of the South America-Antarctica land connection[END_REF]. The onset of the Antarctic Circumpolar Current was associated to a series of climatic and oceanographic changes that play major roles into the distribution and evolution of life in the Southern Ocean.

As a result of its tectonic history, the Southern Ocean is mainly composed of abyssal plains with three deep-water basins surrounding the Antarctic continent (Figure 2; [START_REF] Knox | Biology of the Southern Ocean[END_REF]. The Atlantic-Indian, Indian-Antarctic and Pacific Antarctic basins are partially bounded by a series of ridges, which together with the Kerguelen Plateau and the Scotia Arc tend to restrict or even deflect water circulation from bottom to surface (Figure 2). The Antarctic continental shelf itself has particular geomorphologic features. The enormous pressure exerted by the large mass of ice during ice sheet expansion (isostatic loading), the erosion caused by glacial cycles and iceberg scouring, and the lack of sediment supply from major rivers are at the origin of an over-deepening of the Antarctic continental shelf [START_REF] Post | Environmental Setting. Biogeographic Atlas of the Southern Ocean[END_REF][START_REF] Clarke | Antarctic marine benthic diversity[END_REF][START_REF] Huybrechts | Sea-level changes at the LGM from ice-dynamic reconstructions of the Greenland and Antarctic ice sheets during the glacial cycles[END_REF]. Average depth of the Antarctic continental shelf is about 400 to 700m, representing two to four times the average depth found in other continental shelves in the world [START_REF] Knox | Biology of the Southern Ocean[END_REF][START_REF] Uri | Modelling the bathymetry of the Antarctic continental shelf[END_REF][START_REF] Walsh | On the nature of continental shelves[END_REF]. The topographic reconstruction of Antarctic continental mass (i.e. without ice cover; Figure 2) allows to visualise the occurrence of a possible trans-Antarctic seaway that may have opened during periods of ice sheet collapses [START_REF] Bamber | Reassessment of the potential sea-level rise from a collapse of the West Antarctic Ice Sheet[END_REF][START_REF] Pollard | Modelling west Antarctic ice sheet growth and collapse through the past five million years[END_REF] as a result of complex tectonic processes leading to an aborted rift between West and East Antarctic blocks [START_REF] Fitzgerald | Tectonics and landscape evolution of the Antarctic plate since the breakup of Gondwana, with an emphasis on the West Antarctic Rift System and the Transantarctic Mountains[END_REF].

Both this trans-Antarctic seaway and over-deepening of the Antarctic continental shelf are regarded as conditioning factors of depth and biogeographic distributions of Southern Ocean species [START_REF] Brey | Do Antarctic benthic invertebrates show an extended level of eurybathy?[END_REF][START_REF] Barnes | Faunal evidence for a late Quaternary trans-Antarctic seaway[END_REF][START_REF] Pierrat | Comparative biogeography of echinoids, bivalves and gastropods from the Southern Ocean[END_REF][START_REF] Clarke | Evolution and diversity of the benthic fauna of the Southern Ocean continental shelf[END_REF].

Figure 1 Evolution of the Southern Ocean (modified from [START_REF] Crame | An evolutionary perspective on marine faunal connections between southernmost South America and Antarctica[END_REF]Lawyer & Gahagan, 2003). Paleogeographic reconstructions of the southern continents (south of 30°S) during the Early and Late Cretaceous and during the Early Oligocene. Continental margins and shelves in light beige, continent in dark beige, Antarctica in dark brown.

Climatic history

Mean seawater surface temperatures in the Southern Ocean are low compared to other oceans. In the sub-Antarctic, these temperatures range from 4 to 8°C in summer and from 1 to 3°C during winter. Further south, north of the Antarctic region, they range from 1 to 2°C in winter and 3 to 5°C in summer and often reach values as low as about -1.9°C near the continent (See "Fronts and zonation" for the zonal delineation; [START_REF] Knox | Biology of the Southern Ocean[END_REF]David & Saucède, 2015). These low temperatures are the result of Earth "global cooling" since the Late Mesozoic and the successive climate phases that, from an ice-free world (=Greenhouse global climate/period in the Cretaceous and Paleogene) led to glacial conditions in Antarctica (=Icehouse global climate in the Neogene) [START_REF] Liu | Global cooling during the Eocene-Oligocene climate transition[END_REF]. In Antarctica, its initiation happened around 42 Ma [START_REF] Doria | Declining atmospheric CO2 during the late Middle Eocene climate transition[END_REF] and palaeotemperatures suggest a completion in Figure 2 Subglacial topographic reconstruction of the Southern Ocean (compiled using GEBCO, 2014 and BEDMAP2;Fretwell et al., 2013 grids).

three distinct steps of around 2-3°C (Figure 3; [START_REF] Crame | An evolutionary perspective on marine faunal connections between southernmost South America and Antarctica[END_REF][START_REF] Stott | The evolution of Antarctic surface waters during the Paleogene: Infer-ences from the stable isotope composition of planktonic foraminifers, ODP Leg 113[END_REF]. The onset of the Antarctic Circumpolar Current during the Oligocene [START_REF] Knox | Biology of the Southern Ocean[END_REF][START_REF] Barker | Onset and role of the Antarctic Circumpolar Current[END_REF][START_REF] Siegert | Antarctic climate evolution[END_REF][START_REF] Lefebvre | Deciphering the role of southern gateways and carbon dioxide on the onset of the Antarctic Circumpolar Current[END_REF] and set-up of the deep ocean circulation reduced southward heat transport [START_REF] Toggweiler | Drake Passage and palaeoclimate[END_REF][START_REF] Sijp | Effect of the Drake Passage throughflow on global climate[END_REF], and have played an important role in past climate change by increasing the geographic and climatic isolation of Antarctica (See "Oceanographic features" section).

In the Southern Ocean, this global cooling led to the formation and rapid expansion of Antarctic continental ice-sheets with a major influence on the global climate system, notably on the global water cycle by locking up or releasing vast amounts of freshwater, on the radiative budget through the albedo effect and finally on the thermohaline circulation via freshwater discharged by icecap melting or iceberg calving [START_REF] Eisen | Ground-based measurements of spatial and temporal variability of snow accumulation in East Antarctica[END_REF]. Apart from the Miocene Climatic Optimum that lasted about 15 Myr, temperatures drop continued during the Upper Miocene and accelerated in the Pliocene (5 Ma) until present days to reach the subzero values we currently observe in the vicinity of the Antarctic Continent [START_REF] Zachos | Trends, rhythms, and aberrations in global climate 65 Ma to present[END_REF].

Although the cooling of the Southern Ocean might seem relatively continuous, especially within the last 15 Myr, glacial and interglacial periods, driven by astronomical forcing called the Milankovitch cycles [START_REF] Berger | Milankovitch theory and climate[END_REF] still affect climate and, by extension, the distribution in space and time of Southern Ocean organisms at smaller time scales (several kyr; [START_REF] Clarke | The origin of the Southern Ocean marine fauna[END_REF][START_REF] Brandt | Origin of Antarctic Isopoda (Crustacea, Malacostraca)[END_REF]. [START_REF] Naish | Obliquity-paced Pliocene West Antarctic ice sheet oscillations[END_REF] estimated that at least 38 distinct glacial cycles occurred over the last 5 Myr (Plio-Pleistocene glacial cycles). During these glacial-interglacial cycles, the ice sheet expands and retreats, eradicating habitats from the Antarctic continental shelf with tremendous consequences on the fauna [START_REF] Clarke | The Southern Ocean benthic fauna and climate change: a historical perspective[END_REF][START_REF] Thatje | Effects of capability for dispersal on the evolution of diversity in Antarctic benthos[END_REF].

Molecular and geophysical evidences however suggest that these cycles were not synchronous over the entire continental shelf allowing for ice-free refuges to persist and shelter marine fauna [START_REF] Hemery | Comprehensive sampling reveals circumpolarity and sympatry in seven mitochondrial lineages of the Southern Ocean crinoid species Promachocrinus kerguelensis (Echinodermata)[END_REF][START_REF] Clarke | Evolutionary dynamics at high latitudes: speciation and extinction in polar marine faunas[END_REF][START_REF] Shipp | Seismic signature of the Late Pleistocene fluctuation of the West Antarctic Ice Sheet system in Ross Sea: a new perspective, Part I[END_REF] further details in section "Benthos origin and evolution").

b. Oceanographic features i. Current system in the Southern Ocean

Sea surface currents are mainly the product of stress exerted by the winds on sea surface waters [START_REF] Gordon | Current systems in the Southern Ocean[END_REF]. In the Southern Ocean, strong westerlies (winds blowing eastwards) drive the Antarctic Circumpolar Current (see [START_REF] Rintoul | The Antarctic circumpolar current system[END_REF] for a review), the most powerful current on Earth (140-160 10 6 m³/s). The Antarctic Circumpolar Current flows around the Antarctic Continent with a constriction in the region of the Drake Passage (body of water between Cape Horn and the Antarctic Peninsula) while it reaches over 1,000 km width in the Atlantic sector [START_REF] Knox | Biology of the Southern Ocean[END_REF]. The strong influence of the Antarctic Circumpolar Current on climate [START_REF] Cunningham | Transport and variability of the Antarctic circumpolar current in drake passage[END_REF][START_REF] Griesel | Mean dynamic topography in the Southern Ocean: evaluating Antarctic Circumpolar Current transport[END_REF], on water masses structure [START_REF] Sokolov | Circumpolar structure and distribution of the Antarctic Circumpolar Current fronts: 1. Mean circumpolar paths[END_REF] and thus on Southern Ocean fauna [START_REF] Clarke | How isolated is Antarctica?[END_REF] is no longer to be demonstrated. At higher latitudes, south of 65°S, easterlies (winds blowing westwards)

generate the Antarctic Coastal Current that generally flows along the coastline. Two important indentations in the Ross and Weddell seas are materialised by permanent cyclonic (clockwise) gyres (Figure 4; David & Saucède, 2015;[START_REF] Knox | Biology of the Southern Ocean[END_REF].

At the scale of the World Ocean, the circumpolar expanse of the Southern Ocean over three major oceanic basins (Atlantic, Pacific and Indian oceans) plays a key role in the global ocean circulation (Figure 5). This interbasin connection via the Antarctic Circumpolar Current sustains a global-scale overturning circulation [START_REF] Rintoul | The Antarctic circumpolar current system[END_REF][START_REF] Rintoul | Dynamics of the Southern Ocean circulation[END_REF] with a profound influence on the world's oceans and climate [START_REF] Carter | Circulation and water masses of the Southern Ocean: a review[END_REF] notably through the thermohaline circulation (Figure 5; [START_REF] Park | Thermohaline structure of the Antarctic surface water/winter water in the Indian sector of the Southern Ocean[END_REF]Jacob, 2004). At the surface, wind-driven forcing exerted on water masses creates a northward transport of water (Figure 6). Deep waters follow a same south-north direction, but this transport, feeding the World's ocean with nutrient-rich water masses, is mainly due to variations in water density. At intermediate depths, return flows from the three surrounding basins complete the full cycle of water masses in the overall system (Figure 5 & Figure 6; [START_REF] Sturm | Changes in ocean circulation and carbonate chemistry in the Australian sector of the Southern Ocean during the last 500,000 years[END_REF][START_REF] Carter | Circulation and water masses of the Southern Ocean: a review[END_REF].

ii. Fronts and zonation

Water masses of the Southern Ocean are distributed in accordance with a complex, latitudinal marine front system that was first observed in the early 1930's based on bottlecasts made from the RRS Discovery [START_REF] Deacon | The hydrology of the Southern Ocean[END_REF] and then reviewed by [START_REF] Deacon | Physical and biological zonation in the Southern Ocean. Deep Sea Research Part A[END_REF]. This frontal system induces a latitudinal zonation of the Southern Ocean comprising four frontal zones and two major regions (Figure 7). From North to South, four main fronts can be characterised by steep gradients (warmer and more saline waters north of each front) in seasurface temperature and salinity, delimiting water masses with different densities: (1) the subtropical front or subtropical convergence, which delineates the northern boundary of the Southern Ocean and is positioned at around 45°S, materialises the transition between the sub-Antarctic zone and subtropical latitudes [START_REF] Orsi | On the meridional extent and fronts of the Antarctic Circumpolar Current[END_REF][START_REF] Deacon | Physical and biological zonation in the Southern Ocean. Deep Sea Research Part A[END_REF]; ( 2 Zone to the North and the High Antarctic to the South Figure 7). While these fronts are mainly circumpolar, with the exception of the subtropical front interrupted by South America, their respective latitudinal positions vary with longitude (see Figure 7). The position and permeability of these fronts to marine species dispersal can also vary through time, from seasonal to pluri-millennium time scales. The development of eddies, comparable to current cores crossing the fronts has also been observed [START_REF] Gordon | Spatial and temporal variability within the Southern Ocean[END_REF]. The effect of fronts and eddies on biogeographic patterns is well reported and will be later discussed in this introduction.

Figure 7 Map of the Southern Ocean showing the approximate position of oceanic fronts and associated zones (Figure modified from [START_REF] Knox | Biology of the Southern Ocean[END_REF][START_REF] Orsi | On the meridional extent and fronts of the Antarctic Circumpolar Current[END_REF]

c. A changing world

Since the industrial era, the increase of greenhouse gases released in the atmosphere has driven major environmental changes. Oceans around the world moderate anthropogenic climate change at the cost of profound alterations of their physics, chemistry, ecology, and ecosystem services [START_REF] Gattuso | Contrasting futures for ocean and society from different anthropogenic CO2 emissions scenarios[END_REF]. Whether at the surface or in deep waters, abiotic parameters such as pH, temperature and oxygen content show profound changes and are expected to follow current trends in the future (see Figure 8). Changes induced by human activities since the industrial era know no boundary and are also affecting the Southern Ocean ecosystems in a significant way [START_REF] Summerson | The impact of human activities on wilderness and aesthetic values in Antarctica[END_REF][START_REF] Convey | Terrestrial ecosystem responses to climate changes in the Antarctic[END_REF]. [START_REF] Gutt | The Southern Ocean ecosystem under multiple climate change stresses-an integrated circumpolar assessment[END_REF] summarise the relationships between changes in the environment and the potential effect on biotic and abiotic parameters (Figure 9), showing the complexity of interactions within the Southern Ocean. The rise in Earth's global temperature (as observed today) is expected to continue as described in the 5th Intergovernmental Panel on Climate Change report (IPCC, 2015) and many scientific studies (see [START_REF] Rintoul | Choosing the future of Antarctica[END_REF]. This is, and will continue to affect habitats and organisms of the Southern Ocean through variations in water temperature, salinity, pH (ocean acidification), current or glacial regimes more rapidly than ever observed (Figure 10; [START_REF] Halanych | Challenging Dogma Concerning Biogeographic Patterns of Antarctica and the Southern Ocean[END_REF].

Narratives for the Southern Ocean have been recently presented from the perspective of an observer looking back from 2070 [START_REF] Rintoul | Choosing the future of Antarctica[END_REF]. Under both high and low emissions scenarios, they speculate on future consequences of global change on terrestrial, marine but also in term of human impacts and engagements (see Figure 11). Expected consequences are numerous with notably a rise in air and water temperature of +0.9 to +3°C and +0.7 to +1.9°C respectively, strongly affecting the ice shelf volume and subsequently sea level around the world. Biological communities are not exempted, with an impact on calcification due to ocean acidification, an increase of non-indigenous invasions or profound changes in ecosystems. A more speculative opinion is the incidence of global changes on economic policies for the Southern Ocean, which could lead to an increase in human presence and the use of natural resources (mining, fishing; Figure 11). One of the striking features of Southern Ocean benthic communities is its resemblance with Palaeozoic assemblages (~540 to 250 Ma) in which stalked filter-feeders and echinoderms dominated [START_REF] Dell | Antarctic benthos[END_REF][START_REF] Aronson | Retrograde community structure in the late Eocene of Antarctica[END_REF]. It is however now accepted that these Palaeozoic-like characters (i.e. low-predation, filter-feeder communities) do not result from long survival of an old fauna but rather from similarities in ecological conditions [START_REF] Gili | A unique assemblage of epibenthic sessile suspension feeders with archaic features in the high-Antarctic[END_REF] due to the absence of durophagous species (predators of hard-shelled organisms, [START_REF] Frederich | Distribution patterns of decapod crustaceans in polar areas: a result of magnesium regulation?[END_REF]. The possibility that few representatives of the modern benthic fauna in the Southern Ocean could be extremely old and the result of a long and complex history can however not be discounted [START_REF] Crame | Evolutionary history of Antarctica[END_REF]Crame, 2014). The major issue when trying to estimate the relevance of such old ancestry is the very incomplete marine fossil record [START_REF] Crame | Evolutionary history of Antarctica[END_REF]. Only a small proportion of modern Antarctic groups (i.e. gastropods, asellote isopods, hexactinellid sponges, pycnogonids and gorgonian octocorals) shows scarce but existing evidences of pre-Cenozoic roots [START_REF] Gili | A unique assemblage of epibenthic sessile suspension feeders with archaic features in the high-Antarctic[END_REF][START_REF] Taylor | Evolutionary dynamics of a common sub-Antarctic octocoral family[END_REF][START_REF] Lins | Evidence for Permo-Triassic colonization of the deep sea by isopods[END_REF]Crame et al., 2014;[START_REF] Crame | Key stages in the evolution of the Antarctic marine fauna[END_REF].

The end of the Cretaceous and entrance in the Cenozoic, marked by a mass extinction event (Cretaceous-Paleogene; K-Pl) that took place 66 Ma (Figure 12) is described as a "reset"

in the evolution of life on Earth, leading to a fundamental reorganisation of global marine ecosystems and ultimately to the modern faunas' establishment [START_REF] Stanley | Memoir 4: an analysis of the history of marine animal diversity[END_REF][START_REF] Crame | Key stages in the evolution of the Antarctic marine fauna[END_REF].

This transition, although not instantaneous, was rapid and severe [START_REF] Witts | Macrofossil evidence for a rapid and severe Cretaceous-Paleogene mass extinction in Antarctica[END_REF] and initiated a series of evolutionary phases leading to the contemporary fauna [START_REF] Crame | Key stages in the evolution of the Antarctic marine fauna[END_REF].

ii. Cenozoic evolution of the Antarctic benthos

In his review of key stages in the evolution of the Antarctic marine fauna, [START_REF] Crame | Key stages in the evolution of the Antarctic marine fauna[END_REF] explores in detail the succession of events (Figure 12) that affected benthic and pelagic fauna throughout the Cenozoic era. Although the evolution of Antarctic marine diversity remains largely unknown, a much better picture can now be drawn from integrative paleobiological, molecular and biogeographic studies (coined the macroecological approach by [START_REF] Brown | Macroecology[END_REF].

First, the K-P mass extinction was followed by a phase of intense recovery of biodiversity promoted by ecological opportunities and the evolvability of survivors [START_REF] Crame | Key stages in the evolution of the Antarctic marine fauna[END_REF]. The recovery of biodiversity in the early Cenozoic [START_REF] Bush | Sustained Mesozoic-Cenozoic diversification of marine Metazoa: A consistent signal from the fossil record[END_REF] can be traced back within several taxonomic groups (e.g. decapods crustaceans, teleost fish, molluscs, echinoids) through the few fossiliferous formations (e.g., Sobral Formation and La Meseta Formation in Seymour Island) exposed in Antarctica [START_REF] Zinsmeister | Biogeographic significance of the late Mesozoic and early Tertiary molluscan faunas of Seymour Island (Antarctic Peninsula) to the final breakup of Gondwanaland[END_REF][START_REF] Stilwell | Early Paleocene mollusks of Antarctica: Systematics, paleoecology and paleobiogeographic significance[END_REF][START_REF] Beu | Before the ice: Biogeography of Antarctic Paleogene molluscan faunas[END_REF][START_REF] Saucède | Palaeobiogeography of Austral echinoid faunas: a first quantitative approach[END_REF], Crame et al., 2014).

From the Middle Eocene to the Early Oligocene (~45 to 30 Ma), only scarce evidence is available and should be interpreted with care [START_REF] Crame | Key stages in the evolution of the Antarctic marine fauna[END_REF]. This period coincides with a major cooling of the Southern Ocean following three phases of 2-3°C drops each [START_REF] Stott | The evolution of Antarctic surface waters during the Paleogene: Infer-ences from the stable isotope composition of planktonic foraminifers, ODP Leg 113[END_REF]. It is tempting to link a possible Late Eocene extinction event to these environmental changes, but clear evidence is still lacking [START_REF] Crame | Key stages in the evolution of the Antarctic marine fauna[END_REF]. The physical isolation of Antarctica (see tectonics and geomorphology) being completed at this time together with the onset of glaciation certainly had an effect on the fauna from the Early Oligocene and throughout the Miocene with substantial changes in taxonomic group composition [START_REF] Aronson | Climate change and invasibility of the Antarctic benthos[END_REF]. The fossil record is incomplete by nature, but it suggests a significant extinction event at the Eocene-Oligocene boundary (the "break" of Stehlin; [START_REF] Cavelier | The geological events at the Eocene/Oligocene boundary[END_REF] followed by a series of phased extinctions and radiations at the Oligocene-Miocene transition [START_REF] Crame | Key stages in the evolution of the Antarctic marine fauna[END_REF].

The Middle Miocene marks the last key event in the long evolution of the Antarctic benthos (Figure 12). The intensification of the Antarctic Circumpolar Current, the steep drop in water temperature and the presence of perennial sea-ice cover [START_REF] Crampton | Southern Ocean phytoplankton turnover in response to stepwise Antarctic cooling over the past 15 million years[END_REF] seem to be concordant with major radiation events in the Southern Ocean benthos (e.g. [START_REF] Strugnell | The thermohaline expressway: the Southern Ocean as a centre of origin for deep-sea octopuses[END_REF][START_REF] Janosik | Evolutionary history of Southern Ocean Odontaster sea star species (Odontasteridae; Asteroidea)[END_REF]. Timings of radiations are however different between taxonomic groups [START_REF] Verheye | Locked in the Icehouse: evolution of an endemic Epimeria (Amphipoda, Crustacea) species flock on the Antarctic shelf[END_REF][START_REF] González-Wevar | Following the Antarctic Circumpolar Current: patterns and processes in the biogeography of the limpet Nacella (Mollusca: Patellogastropoda) across the Southern Ocean[END_REF][START_REF] Dueñas | The Antarctic Circumpolar Current as a diversification trigger for deep-sea octocorals[END_REF][START_REF] Barco | Cenozoic evolution of Muricidae (Mollusca, Neogastropoda) in the Southern Ocean, with the description of a new subfamily[END_REF]Diaz et al., 2011) and may be linked to the dynamics of ice advances and retreats during Pliocene-Pleistocene glacial-interglacial cycles rather than to the Middle Miocene Climatic Transition. This succession of glacial inter-glacial periods, at least 38 during the last 5 Myr [START_REF] Naish | Obliquity-paced Pliocene West Antarctic ice sheet oscillations[END_REF], may have triggered these radiations. The so-called "Antarctic diversity pump" [START_REF] Clarke | The Southern Ocean benthic fauna and climate change: a historical perspective[END_REF] resulting from glacial eradications of shelf habitats, subsistence in deep or ice-free isolated refuges followed by recolonisations and migrations in and out of Antarctica has indeed been suggested as a strong driver of species diversification in many genetic studies (e.g [START_REF] Near | Ancient climate change, antifreeze, and the evolutionary diversification of Antarctic fishes[END_REF][START_REF] Havermans | Phylogeographic Patterns of the Lysianassoidea (Crustacea: Peracarida: Amphipoda). Biogeographic atlas of the Southern Ocean[END_REF][START_REF] Rogers | Evolution and biodiversity of Antarctic organisms: a molecular perspective[END_REF].

In summary, the present composition of the Southern Ocean fauna is believed to have several origins:

-A relict autochthonous fauna of Gondwanian origin that survived the K-P extinction and the Eocene cooling phase (applicable to the Antarctic and sub-Antarctic fauna).

-A deep-sea fauna that colonised the Antarctic shelf from the deep ocean basins and via the deep Antarctic shelf and slope (i.e. Polar Emergence hypothesis) (applicable to the Antarctic and sub-Antarctic zones fauna).

-A Magellanic component that colonised via dispersal along the Scotia Arc (applicable to the Antarctic fauna) or dispersal via the Antarctic Circumpolar Current (applicable to the sub-Antarctic fauna).

-A northern fauna migrating to the Southern Ocean (applicable to the Antarctic and sub-Antarctic fauna). Either from tropical latitudes (Out of the Tropic scenario) via South American or Indo-West Pacific regions or via deep sea routes.

-In situ diversifications following all the previously mentioned scenarios. Whether catalysed by geographic isolation in glacial refuges (see section "genetic diversity patterns"), on the many islands surrounding Antarctica or induced by oceanographic (e.g.

Antarctic Circumpolar Current) or biological (e.g. reproductive strategy) factors; the uniqueness of current biodiversity is the result of in situ evolution.

It is however important to note that these potential origins imply the probable subsequent colonisation via dispersal and/or migration of taxa in and out of their respective zones making the identification of centres of origin rather complicated.

b. Modern benthic life in the Southern Ocean i. A century of discoveries

Being the last to be discovered, regions of the Southern Ocean and Antarctica have only been recently surveyed and remain underexplored for a large part [START_REF] Clarke | Antarctic marine benthic diversity[END_REF][START_REF] Clarke | How well do we know the Antarctic marine fauna? A preliminary study of macroecological and biogeographical patterns in Southern Ocean gastropod and bivalve molluscs[END_REF][START_REF] Griffiths | Data distribution: Patterns and implications. Biogeographic atlas of the Southern Ocean[END_REF]. The dramatic seasonal variations in sea-ice cover that can double during the austral winter (Figure 13; [START_REF] Zwally | Antarctic sea ice, 1973-1976: Satellite passive-microwave observations[END_REF]Comiso & Zwally, 1984), extreme weather and sea conditions (e.g. sub-zero temperatures, strong winds), the important depth of the seabed are all limiting factors to marine life investigations.

The Heroic Age of Exploration (1895-1922 however witnessed the beginning of systematic and comprehensive scientific sampling in Antarctica starting with the Belgica expedition in 1897- Over the last fifty years, the establishment of scientific stations and supply-ship routes have promoted a major increase in the collection of biological samples [START_REF] Griffiths | Data distribution: Patterns and implications. Biogeographic atlas of the Southern Ocean[END_REF] and international census projects (Census of Antarctic Marine Life, starting 2005;International Polar Year, 2007-2008) have allowed a better understanding of the Southern Ocean, its unique environments and dynamics.

ii. Particularisms of the benthic fauna

Benthic environmental conditions in the Southern Ocean have traditionally been considered as cold and thermally stable [START_REF] Post | Environmental Setting. Biogeographic Atlas of the Southern Ocean[END_REF] with seasonal variation in food availability and greater shelf depths in comparison to other oceans [START_REF] Knox | Biology of the Southern Ocean[END_REF]. Such extreme conditions (water temperatures below 0°C, absence of food intake for months, high impact of iceberg scouring) might appear harsh for life to develop in the Southern Ocean. It is however clear that although communities are very different from other regions, they thrive in these environments despite their apparent harshness [START_REF] Picken | Marine habitats-benthos[END_REF].

Antarctic benthic organisms are generally described to have unique biological traits such as an important longevity and late maturity, gigantism, slow growth rate. The fauna shows high level of endemism and metabolic adaptations to cold waters [START_REF] White | Marine benthos[END_REF][START_REF] Howe | Deep-water sedimentary environments of the northwestern Weddell Sea and South Sandwich Islands, Antarctica[END_REF][START_REF] Knox | Biology of the Southern Ocean[END_REF][START_REF] Halanych | Challenging Dogma Concerning Biogeographic Patterns of Antarctica and the Southern Ocean[END_REF]. Environmental and geographic settings seem to have driven these attributes, especially cold sea water temperatures, and oceanographic and geographic isolation [START_REF] Pörtner | Climate-dependent evolution of Antarctic ectotherms: an integrative analysis[END_REF][START_REF] Howe | Deep-water sedimentary environments of the northwestern Weddell Sea and South Sandwich Islands, Antarctica[END_REF].

Figure 14 The rate of description of Southern Ocean species. Figure from [START_REF] Griffiths | Antarctic marine biodiversity -what do we know about the distribution of life in the Southern Ocean?[END_REF].

Another singularity of Southern Ocean benthic fauna is the high incidence of parental care in invertebrates [START_REF] Poulin | Evolutionary versus ecological success in Antarctic benthic invertebrates[END_REF][START_REF] Pearse | Brooding and species diversity in the Southern Ocean: selection for brooders or speciation within brooding clades? Smithsonian at the poles: contributions to international polar year science[END_REF]. For a long time, brooding has been observed (e.g. [START_REF] Thomson | Notice of some peculiarities on the mode of propagation of certain echinoderms of the southern seas[END_REF] in higher proportions in the Southern Ocean than in other oceans [START_REF] Mileikovsky | Types of larval development in marine bottom invertebrates, their distribution and ecological significance: a re-evaluation[END_REF]. The origin of this unusually high number of brooding species with no larval phase in their development is probably to be related to vicariance and allopatric speciation rather than to a consequence of adaptation to freezing conditions [START_REF] Poulin | Evolutionary versus ecological success in Antarctic benthic invertebrates[END_REF][START_REF] Pearse | Brooding and species diversity in the Southern Ocean: selection for brooders or speciation within brooding clades? Smithsonian at the poles: contributions to international polar year science[END_REF]. Two main biogeographic processes at play here lead to the isolation of populations: a persistence in refuges on the continental shelf during Pliocene-Pleistocene glacial maxima (See "genetic diversity patterns") and/or the transport of propagules to new and remote habitats, especially around the Scotia Arc [START_REF] Pearse | Brooding and species diversity in the Southern Ocean: selection for brooders or speciation within brooding clades? Smithsonian at the poles: contributions to international polar year science[END_REF]. Brooding has not been without consequence for the evolution, diversity and biogeography of Antarctic fauna.

Its significance for understanding phylogeographic relationships between clades is important (e.g. [START_REF] Hoffman | Effects of brooding and broadcasting reproductive modes on the population genetic structure of two Antarctic gastropod molluscs[END_REF][START_REF] Hellberg | Genetic assessment of connectivity among marine populations[END_REF] and will be further discussed and investigated for sea stars in the present thesis.

Similarly, the general view of a low marine diversity in the Southern Ocean has been subject to many discussions [START_REF] Gutt | How many macrozoobenthic species might inhabit the Antarctic shelf?[END_REF] and was first thought to be due to harsh environmental conditions. Many studies then proved this assumption to be erroneous [START_REF] Dell | Antarctic benthos[END_REF][START_REF] Arntz | Antarctic marine biodiversity: an overview. Antarctic communities: species, structure and survival[END_REF][START_REF] Clarke | Antarctic marine benthic diversity[END_REF] albeit varying across taxonomic groups. The macrofauna richness of the Antarctic continental shelf was estimated to exceed 17,000 species [START_REF] Gutt | How many macrozoobenthic species might inhabit the Antarctic shelf?[END_REF] when only around 7,600 marine species have been described (data from the Register of Antarctic Marine Species, De Broyer et al., 2019;[START_REF] Jossart | The Register of Antarctic Marine Species (RAMS): a ten-year appraisal[END_REF]. This suggests that diversity is strongly underestimated in the Southern Ocean, which together with a scattered sampling effort (see Figure 15; Griffith et al., 2014) and the increase of molecular data showing the inaccuracy of species richness evaluation (e.g. [START_REF] Janosik | Evolutionary history of Southern Ocean Odontaster sea star species (Odontasteridae; Asteroidea)[END_REF]Jossart et al., 2019) suggests diversity levels comparable to temperate and certain tropical non-reef areas [START_REF] Clarke | Antarctic marine benthic diversity: patterns and processes[END_REF].

c. Biogeography and phylogeography of modern Antarctic benthic faunas

The climatic and tectonic history of the Southern Ocean and the evolution of its benthic fauna, as described in the previous sections, have had major consequences on the present distribution of benthic life. Macroecology has been defined as a research area using quantitative ecology, macroevolution, phylogeography and biogeography in an integrative approach to characterise patterns of species abundance and distribution [START_REF] Brown | Macroecology[END_REF][START_REF] Keith | What is macroecology?[END_REF]. Using the macroecological approach (to investigate patterns of species distribution and genetic structures in space) allows to untangle the relative importance of the driving factors that underpin the observed patterns.

The biogeographical approach is based on the study of faunal compositions and relationships among bioregions that are, geographical areas characterised by their species assemblages. Studying sea star assemblages will allow to identify faunal similarities among bioregions and infer their existing or past connectivity while trying to relate them to historical or contemporaneous processes (e.g. onset of the Antarctic Circumpolar Current).

Phylogeographic works, on the other hand, are comparatively new and deal with the analysis of the spatial arrangement of genetic lineages within closely related taxa [START_REF] Avise | Phylogeography: retrospect and prospect[END_REF]. By taking into account both spatial and temporal dimensions, phylogeography represents a powerful tool to complement the biogeographical approach and is often considered as an extension of it.

i. Biogeographic regions in the Southern Ocean

First biogeographical studies in the Southern or other oceans were carried out by ichthyologists [START_REF] Regan | Fishes. British Antarctic ("Terra Nova"). Expedition[END_REF][START_REF] Nybelin | Antarctic fishes. The Scientific Results of the Norwegian Antarctic Expedition[END_REF]. Regarding benthic organisms, [START_REF] Knox | Littoral ecology and biogeography of the southern oceans[END_REF] and [START_REF] Hedgpeth | Introduction to Antarctic zoogeography. Distribution of selected groups of marine invertebrates in water south of 35[END_REF] undertook pioneering studies on the biogeography of the Southern Ocean.

Based on faunal affinities, [START_REF] Hedgpeth | Introduction to Antarctic zoogeography. Distribution of selected groups of marine invertebrates in water south of 35[END_REF] recognised two main regions, the Antarctic and the sub-Antarctic, themselves also subdivided into smaller subregions and districts (see Figure 16).

Figure 16 Biogeographic divisions of the Southern Ocean proposed by [START_REF] Hedgpeth | Introduction to Antarctic zoogeography. Distribution of selected groups of marine invertebrates in water south of 35[END_REF].

Since then, several studies have refined these founding works using compiled databases and modern computational statistic tools (e.g. [START_REF] Pierrat | Comparative biogeography of echinoids, bivalves and gastropods from the Southern Ocean[END_REF]. Focusing on individual taxa, these surveys have documented new distribution patterns at smaller scale that are taxon-dependent (e.g. hydroids, Mercado Casares et al., 2017;echinoids, bivalves and gastropods, Pierrat et al., 2013;sea anemones, Rodriguez et al., 2007). Some of the main patterns defined by [START_REF] Hedgpeth | Introduction to Antarctic zoogeography. Distribution of selected groups of marine invertebrates in water south of 35[END_REF], such as the separation between sub-Antarctic and Antarctic regions and the distinctiveness of South Georgia, remain undebated today (De Broyer et al., 2014). Other patterns, such as the unity of the continental subregion have been questioned as they were shown to be highly dependent on the taxa under study (David & Saucède, 2015;De Broyer et al., 2014).

At a very large spatial scale, benthic life usually shows a general pattern of decreasing species richness from the low to the high latitudes, following a well-documented latitudinal gradient of diversity [START_REF] Lomolino | Biogeography[END_REF]. In the marine realm, there is evidence of an asymmetric distribution of species richness between the poles, with the Southern Ocean being richer than the Arctic because of the relatively young age of the Arctic Ocean isolation (2-3 Myr) [START_REF] Crame | Frontiers of biogeography: new directions in the geography of nature[END_REF][START_REF] Gray | Antarctic marine benthic biodiversity in a world-wide latitudinal context[END_REF]. Longitudinal contrasts are also apparent between the rich areas surrounding New Zealand and the comparatively poorer Magellanic area (David & Saucède, 2015). Recent developments and the popularisation of molecular tools in concert with an increased availability of samples are however bringing new insights on the distribution of life in the Southern Ocean based on quantitative and objective approaches [START_REF] Held | Phylogeography and population genetics[END_REF].

ii. Genetic diversity patterns

One of the main limiting factors of traditional biogeography is its foundation on morphology-based taxonomy that can be subject to mis-interpretations of taxon diversity.

Often applied to small taxonomic and geographical entities, genetic tools can be very powerful to infer faunal affinities among localities and taxonomic units. Not only have these tools helped better understand how life is distributed in the Southern Ocean, they also identified and pinpointed the poor knowledge and/or misinterpretation of taxonomic units based on morphological characters only [START_REF] Held | Phylogeography and population genetics[END_REF]. One of the first outcomes of the widespread use of molecular tools in the Southern Ocean is the frequent discovery of unrecognised species, which can be defined as cryptic in the absence of a discriminant morphological characters (e.g. Pfenninger & Schwenk, 2007;[START_REF] Brasier | DNA barcoding uncovers cryptic diversity in 50% of deep-sea Antarctic polychaetes[END_REF][START_REF] Jossart | Dwarf brooder versus giant broadcaster: combining genetic and reproductive data to unravel cryptic diversity in an Antarctic brittle star[END_REF]. The numerous divergent lineages recently documented in the Southern Ocean are probably the evolutionary consequence of the successive Pliocene-Pleistocene glacial cycles but also to the limited dispersal capacities of certain taxa. Glacial cycles have shaped diversity by vicariance due to the fragmentation of the taxon distribution range during glacial maxima and the survival of small genetic units into refuges (Allcock & Strugnell, 2012). Molecular data obtained from the analysis of contemporary benthic populations have permitted the identification of several types of refuges:

The Deep sea and upper slope

These refuges have been identified as the main explanation of the apparent extreme eurybathy of many species in the Southern Ocean with many recurrent migration events occurring from shallow to deep environments and back. Although there are molecular evidences suggesting that eurybathy is less prevalent than previously believed, some casestudies still support the deep-sea refugia hypothesis (e.g. [START_REF] Havermans | DNA barcoding reveals new insights into the diversity of Antarctic species of Orchomene sensu lato (Crustacea: Amphipoda: Lysianassoidea). Deep Sea Research Part II[END_REF][START_REF] Arango | Genetic differentiation in the circum-Antarctic sea spider Nymphon australe (Pycnogonida; Nymphonidae)[END_REF].

The continental shelf

Subsistence of populations on the Antarctic continental shelf is probably the most reported type of refuges in the Southern Ocean. Whether resulting from asynchronous ice advances, uncovered areas always free of ice, the permanence of polynyas or natural barriers, many transitional refuges may have sheltered marine fauna locally (David & Saucède, 2015;Allcock & Strugnell, 2012). There are numerous case studies documenting such a process across a wide range of taxa (e.g. echinoids, [START_REF] Díaz | Evolutionary pathways among shallow and deep-sea echinoids of the genus Sterechinus in the Southern Ocean[END_REF]nemertean, Thornhill et al., 2008).

The sub-Antarctic islands

The last putative glacial refuges in the Southern Ocean correspond to the subsistence of populations around the sub-Antarctic islands including the subsequent colonisation of higher latitudes after the main ice retreats. This type of refugia seems to explain the genetic patterns of some widespread species (e.g. Promachocrinus kerguelensis, [START_REF] Hemery | Comprehensive sampling reveals circumpolarity and sympatry in seven mitochondrial lineages of the Southern Ocean crinoid species Promachocrinus kerguelensis (Echinodermata)[END_REF].

However, the possibility that species now restricted to the high Antarctic region found shelter uniquely on sub-Antarctic islands seems unlikely (Allcock & Strugnell, 2012).

Another strength of molecular analyses resides in its temporal dimension. Based on the "molecular clock" hypothesis, analyses allow to estimate timings of divergence within taxa. This approach is more and more frequently used to date and relate genetic patterns with climatic or tectonic-driven events of vicariance or dispersal. Most recent studies using these tools suggest that radiations recently occurred within the past 5 to 10 Myr, challenging the former idea that present-day patterns mainly result from the much older opening of the Drake Passage and subsequent isolation of Antarctic waters (e.g. [START_REF] Sands | Against the flow: evidence of multiple recent invasions of warmer continental shelf waters by a Southern Ocean brittle star[END_REF]Thornill et al., 2008;[START_REF] Janosik | Evolutionary history of Southern Ocean Odontaster sea star species (Odontasteridae; Asteroidea)[END_REF].

Finally, the last benefit when using genetic data is the delineation of taxonomical units resulting from challenging molecular results. These techniques -often based on a fragment of the sole mitochondrial marker COI (i.e. barcode sequence or Cytochrome c Oxidase subunit I) are based on either tree reconstruction (e.g. GMYC) or genetic distances (e.g. ABGD). They are expected to produce impartial taxonomical units considered as putative species. Nominal species are the working units in a number of studies, far beyond the scope of taxonomy (e.g.

species distribution modelling, physiology, biogeography, conservation). It is therefore crucial to use appropriate methods to define robust taxonomic units and ensure relevant scientific outputs. However, there are still many limitations to the use of molecular tools, despite the increasing development of barcode sequences. Introgression, nuclear pseudogenes, lack of representativeness of the whole genome can be problematic. The fact that species delineation methods rely on the concept that intraspecific divergences will be always less marked than interspecific ones (the barcode gap) can also be questionable, especially when taxa have been going through rapid and recent radiations as observed in the Southern Ocean (Allcock & Strugnell, 2012;Monaghan et al., 2006).

Despite these limitations, the development of barcoding has resulted in a substantial contribution to taxonomy, population genetics and molecular phylogenetics [START_REF] Hajibabaei | DNA barcoding: how it complements taxonomy, molecular phylogenetics and population genetics[END_REF]. There is still a crucial need to increase the number of sampled taxa to better document Antarctic benthic life in space and its evolution through time but also for phylogenetic reconstructions [START_REF] Hajibabaei | DNA barcoding: how it complements taxonomy, molecular phylogenetics and population genetics[END_REF]. In a period of growing interest in the setting up and management of marine protected areas, accurate and comprehensive barcode libraries should receive more consideration. By providing a reference for specimen identification, especially for poorly studied taxa, such databases can prevent from misinterpretations of taxonomic data. It is nevertheless evident, that such an effort as to go in concert with morphological identification (i.e. integrative taxonomy approach; [START_REF] Dayrat | Towards integrative taxonomy[END_REF].

iii. Consequences of reproductive strategies on diversity patterns

In biogeography and phylogeography, homogeneous distribution patterns are expected to be more likely in species including a pelagic larval stage in their development (i.e.

broadcasters) compared to other species without such a stage (i.e. brooders; [START_REF] Held | Phylogeography and population genetics[END_REF].

Both strategies are well represented in the Southern Ocean with for example, over 50% of brooding species in brittle stars, sea stars (see Figure 17) and sea urchins (David & Saucède, 2015). Because of homogenising factors such as the Antarctic Circumpolar Current [START_REF] Held | Phylogeography and population genetics[END_REF], many early biogeographic works assumed that most Southern Ocean species were circumpolar and structured into a single taxonomic entity [START_REF] Hedgpeth | Introduction to Antarctic zoogeography. Distribution of selected groups of marine invertebrates in water south of 35[END_REF][START_REF] Clarke | Evolution and adaptive radiation of Antarctic fishes[END_REF][START_REF] Arntz | Antarctic zoobenthos[END_REF].More recent studies however demonstrate that the relationship between reproduction and population genetic structures is not as evident as previously thought [START_REF] Halanych | Challenging Dogma Concerning Biogeographic Patterns of Antarctica and the Southern Ocean[END_REF]. While some broadcasting species display homogeneous genetic patterns on large spatial scale as formerly expected (e.g. [START_REF] Matschiner | Gene flow by larval dispersal in the Antarctic notothenioid fish Gobionotothen gibberifrons[END_REF][START_REF] González-Wevar | Molecular phylogeny and historical biogeography of Nacella (Patellogastropoda: Nacellidae) in the Southern Ocean[END_REF], other broadcasters show spatially structured genetic signals (e.g. [START_REF] Hunter | Phylogeography of the Antarctic planktotrophic brittle star Ophionotus victoriae reveals genetic structure inconsistent with early life history[END_REF][START_REF] Hoffman | Unexpected fine-scale population structure in a broadcast-spawning Antarctic marine mollusc[END_REF]. Similarly, species with direct development show contrasting genetic structures with either strong (e.g. [START_REF] Hoffman | Effects of brooding and broadcasting reproductive modes on the population genetic structure of two Antarctic gastropod molluscs[END_REF] or weak spatial patterns (e.g. [START_REF] Wilson | Ocean barriers and glaciation: evidence for explosive radiation of mitochondrial lineages in the Antarctic sea slug Doris kerguelenensis (Mollusca, Nudibranchia)[END_REF][START_REF] Fraser | Genetic affinities between trans-oceanic populations of non-buoyant macroalgae in the high latitudes of the Southern Hemisphere[END_REF].

Empirical evidences indicate that, although reproductive strategy affects the distribution of Southern Ocean species and the connectivity between populations, other mechanisms can be important [START_REF] Halanych | Challenging Dogma Concerning Biogeographic Patterns of Antarctica and the Southern Ocean[END_REF]: 1) The mobility of adults and passive rafting are suspected to promote dispersal; 2) Kelp rafting in the Southern Ocean was shown in sea stars and crustaceans [START_REF] Waters | Rafting dispersal in a brooding southern sea star (Asteroidea: Anasterias)[END_REF][START_REF] Nikula | Circumpolar dispersal by rafting in two subantarctic kelp-dwelling crustaceans[END_REF] while rafting on iceberg transporting seafloor debris and invertebrates (gastropods, echinoids) has been observed [START_REF] Peck | Antarctic marine biodiversity: Adaptations, environments and responses to change[END_REF]; 3) Anthropogenic debris such as plastics have also been identified as possible dispersal vectors [START_REF] Barnes | Biodiversity: invasions by marine life on plastic debris[END_REF][START_REF] Eriksen | Plastic pollution in the world's oceans: more than 5 trillion plastic pieces weighing over 250,000 tons afloat at sea[END_REF]).

d. Sea stars in the Southern Ocean i. General overview

The class Asteroidea, commonly referred to as sea stars or starfish, is the second most diverse class within the phylum Echinodermata. With ~1,900 accepted species names (and many more remaining to be described), sea stars are important components of marine ecosystems [START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF] and are widely distributed (from the intertidal to more than 6,500 m depth). Sea stars display high ecological diversity (e.g. [START_REF] Jangoux | Food and feeding mechanisms: Asteroidea[END_REF] and are important into organising benthic marine communities [START_REF] Menge | Ecological Role of Sea Stars from Populations. Starfish: biology and ecology of the Asteroidea[END_REF]. Their taxonomic diversity is also high with 38 families and 344 genera [START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF].

Worldwide diversity patterns of sea stars have been roughly described with the highest species richness found in tropical regions (e.g. [START_REF] Blake | Adaptive zones of the class Asteroidea (Echinodermata)[END_REF]) and a latitudinal diversity gradient decreasing towards the poles with however a lower richness in the Arctic than in the Antarctic [START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF]. Despite this richness gradient at species level, cold waters of high latitudes harbour a much higher family-level richness [START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF].

Generally speaking, sea stars have been used as case studies in numerous biological fields, from benthic community studies (e.g. [START_REF] Gianguzza | Sizedependent predation of the mesopredator Marthasterias glacialis (L.)(Asteroidea)[END_REF][START_REF] Analuddin | Spatial Pattern in Beta Diversity of Echinoidea and Asteroidea Communities from the Coastal Area of Tomia Island, Wakatobi Marine National Park, Southeast Sulawesi, Indonesia[END_REF] to physiological works on the effect of environmental stressors (e.g. [START_REF] Magesky | Molecular Stress Responses against Trace Metal Contamination in Aquatic Invertebrates[END_REF][START_REF] Kamya | Near-future ocean acidification enhances the feeding rate and development of the herbivorous juveniles of the crown-of-thorns starfish, Acanthaster planci[END_REF], parasitology [START_REF] Takano | Molecular phylogenetic investigations of the relationships of the echinoderm-parasite family Eulimidae within Hypsogastropoda (Mollusca)[END_REF] and immunology [START_REF] Leclerc | Cell-Mediated and Humoral Immune Responses in the Sea-Star Asterias Rubens (Echinoderm): Notion of Invertebrate Primitive Antibody[END_REF].

Despite this interest, the global phylogeny of the class Asteroidea has been controversial for more than 100 years (Lawrence, 2013; Figure 18) and is still subject to discussions, debates and extensive works [START_REF] Janies | Echinoderm phylogeny including Xyloplax, a progenetic asteroid[END_REF][START_REF] Linchangco | The phylogeny of extant starfish (Asteroidea: Echinodermata) including Xyloplax, based on comparative transcriptomics[END_REF]. The authors however tend to agree on the common origin of all modern sea stars: the sub-class Neoasteroidea [START_REF] Gale | Phylogeny and classification of the Asteroidea (Echinodermata)[END_REF][START_REF] Blake | A classification and phylogeny of post-Palaeozoic sea stars (Asteroidea: Echinodermata)[END_REF]. Representatives of the Neoasteroidea are believed to have evolved from a single common ancestor that survived to the Permian-Triassic extinction [START_REF] Gale | Phylogeny and classification of the Asteroidea (Echinodermata)[END_REF]2011) and then diversified following an evolutionary pattern common to all five classes echinoderms [START_REF] Chen | End-Permian extinction and subsequent recovery of the Ophiuroidea (Echinodermata)[END_REF][START_REF] Twitchett | Early Triassic recovery of echinoderms[END_REF]. Recent fossil findings and phylogenetic results however question this over-simplified interpretation of the post-Palaeozoic diversification of echinoderms (e.g. [START_REF] Villier | Superstesaster promissor gen. et sp. nov., a new starfish (Echinodermata, Asteroidea) from the Early Triassic of Utah, USA, filling a major gap in the phylogeny of asteroids[END_REF].

ii. Southern Ocean sea stars

In the Southern Ocean, sea stars are also well represented with 12% of the class global species richness recorded in the region [START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF]. Evidences regarding their origin around the Antarctic continent are only scarce but fossils tend to show that Southern Ocean sea stars follow the same general trend as benthic organisms in their evolution (see "Origin and evolution of the Antarctic benthos"). The presence of an extinct asteroid fauna including highly calcified members of Goniasteridae and Oreasteridae [START_REF] Blake | Eocene stelleroids (Echinodermata) at Seymour Island, Antarctic Peninsula[END_REF] during the Eocene indicates that no autochthonous sea star fauna survived the cooling of Antarctica while these faunas are still present in other regions. Current phylogenetic evidences argue for a recent diversification in the Southern Ocean and a possible ancestry from adjacent sub-Antarctic regions (Mah & Foltz, 2011a, 2011b;[START_REF] Janosik | Evolutionary history of Southern Ocean Odontaster sea star species (Odontasteridae; Asteroidea)[END_REF].

In the Southern Ocean, as in other oceans, sea stars are common benthic organisms found in diverse environments from the intertidal to the abyss (Figure 19; [START_REF] Brandt | First insights into the biodiversity and biogeography of the Southern Ocean deep sea[END_REF]Linse et al., 2007a;[START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF]. They have been studied since the late 19th century in the Southern Ocean (e.g. [START_REF] Sladen | Report on the scientific results of the voyage of HMS Challenger during the years 1873-76[END_REF] with scientific work documenting their ecological importance to southern ecosystems (McClintock et al., 2008;[START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF][START_REF] Lawrence | Starfish: biology and ecology of the Asteroidea[END_REF]. However, the vast majority of studies carried out around Antarctica focused on the sole abundant near-shore species Odontaster validus (e.g. [START_REF] Janosik | Evolutionary history of Southern Ocean Odontaster sea star species (Odontasteridae; Asteroidea)[END_REF][START_REF] Agüera | Parameter estimations of Dynamic Energy Budget (DEB) model over the life history of a key Antarctic species: the Antarctic sea star Odontaster validus Koehler[END_REF][START_REF] Pearse | Photoperiodic regulation of gametogenesis in the Antarctic sea star Odontaster validus Koehler: evidence for a circannual rhythm modulated by light[END_REF] known for its key position in shallow benthic communities of the Southern Ocean [START_REF] Dayton | Toward an understanding of community resilience and the potential effects of enrichments to the benthos at McMurdo Sound, Antarctica[END_REF]McClintock et al., 2008). Odontaster validus has notably been used as a model species in studies on the consequences of global change on Antarctic organisms (e.g. [START_REF] Peck | Temperature limits to activity, feeding and metabolism in the Antarctic starfish Odontaster validus[END_REF][START_REF] Gonzalez-Bernat | Effects of reduced seawater pH on fertilisation, embryogenesis and larval development in the Antarctic seastar Odontaster validus[END_REF]. However, little is known about overall distribution patterns (Danis et al., 2014;[START_REF] Moles | Distribution patterns in Antarctic and Subantarctic echinoderms[END_REF], diversity [START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF] and evolution of sea stars in the Southern Ocean and even less about the underpinning mechanisms that drive them. The last census of asteroid diversity conducted in the framework of this thesis gives estimates of ~300 species in the Southern Ocean (Asteroidea Database and species list) emphasising the potential richness of the Southern Ocean sea stars and their quality as a target group for large scale studies and meta-analyses in diversity, connectivity and distribution studies.

As previously mentioned, sea stars have diverse reproduction modes (e.g. [START_REF] Mcclintock | The biochemical composition, energy content, and chemical antifeedant defenses of the common Antarctic Peninsular sea stars Granaster nutrix and Neosmilaster georgianus[END_REF] and possibly the complete range of this biological function described in the phylum Echinodermata [START_REF] Naughton | A new brooding species of the biscuit star Tosia (Echinodermata: Asteroidea: Goniasteridae), distinguished by molecular, morphological and larval characters[END_REF]. As for several other benthic groups (e.g. Amphipoda, Echinoidea), brooding, which can take many forms in sea stars (e.g. in the stomach pouch, within brood chambers, on the dorsal surface) seems to occur in an unusually high number of species in the Southern Ocean [START_REF] Pearse | Brooding and species diversity in the Southern Ocean: selection for brooders or speciation within brooding clades? Smithsonian at the poles: contributions to international polar year science[END_REF]. Broadcasting species are however well represented too, and in contrast with brooding members their offspring can spend more than five months in the water column [START_REF] Bosch | Developmental types of shallow-water asteroids of McMurdo Sound, Antarctica[END_REF]. Such diverging life history traits may have certainly conditioned distribution and diversity patterns along asteroid evolution.

Molecular investigations of the diversity and connectivity between Southern Ocean sea stars are limited but indicate an overlooked diversity in the best studied representative of the class: Odontaster validus [START_REF] Janosik | Evolutionary history of Southern Ocean Odontaster sea star species (Odontasteridae; Asteroidea)[END_REF]. Another work by [START_REF] Moore | The Antarctic Circumpolar Current isolates and connects: Structured circumpolarity in the sea star Glabraster antarctica[END_REF] explored phylogeographic patterns in Glabraster antarctica, a conspicuous sea star in the Southern Ocean, and confirmed that the species is highly polymorphic but constitutes a single entity as proposed by morphological work [START_REF] Mah | New taxa and taxonomic revisions to the Poraniidae (Valvatacea; Asteroidea) with comments on feeding biology[END_REF]. This does not preclude to the occurrence of strong phylogeographic structures between populations of this species [START_REF] Moore | The Antarctic Circumpolar Current isolates and connects: Structured circumpolarity in the sea star Glabraster antarctica[END_REF]. Finally, a joint effort in the sampling of Anasterias suteri along the shore and on floating kelps in the sub-Antarctic, showed the prevalence of genetic connectivity between geographically distant populations of this brooding species [START_REF] Waters | Rafting dispersal in a brooding southern sea star (Asteroidea: Anasterias)[END_REF]. At a higher taxonomic level, the phylogeny and evolutionary history of the Asteroidea in the Southern Ocean has also been discussed in several studies (Mah & Foltz, 2011a, 2011b, 2014;[START_REF] Mah | Description of a new family, new genus, and two new species of deep-sea Forcipulatacea (Asteroidea), including the first known sea star from hydrothermal vent habitats[END_REF]. In their comprehensive molecular phylogeny of the superorders Valvatacea and Forcipulatacea, Mah & Foltz (2011a, b) described some diversification processes in several Antarctic and sub-Antarctic families (e.g. Odontasteridae, Antarctic Asteriidae) and a possible ancestry from surrounding regions. They however did not analyse lower taxonomic levels (i.e., genera and species). Being the last discovered ocean and despite an intense, coordinated scientific effort over the last decades, biodiversity of the Southern Ocean is still poorly documented and understood. Here, I propose to use sea stars, a common, diverse and important component of Southern Ocean benthic communities as a model taxon to analyse large scale distribution and diversity patterns and their putative evolutionary origin.

The first objective of the present work aims at describing and analysing distribution patterns at the scale of the entire Southern Ocean within the whole Asteroidea class. This chapter includes the study of the role of a life history trait on the observed patterns: the reproductive strategy (brooding versus broadcasting). I hypothesize that the limited to null ability of species without a pelagic larval phase (i.e. brooders) to disperse will result in noticeable distribution patterns on large spatial and temporal scales. Species with a pelagic phase (i.e. broadcasters) will on the contrary exhibit less structure due to a constant mixing over time. I expect, in this chapter, to show which faunal affinities can be observed among the main bioregions of the Southern Ocean and to deduce which drivers (biotic and abiotic) are influencing these patterns. This biogeographical approach is based on an extensive georeferenced database that includes mention of the respective reproduction strategy (see Asteroidea Database).

The second objective aims at complementing the first one with an approach based on molecular tools. A phylogeographical approach is used to evaluate the effect of contrasting reproductive strategy (brooding versus broadcasting) and the distinct dispersal capacities of species on genetic diversity and structure of Southern Ocean sea stars. Using five genera (three brooding ones and two broadcasting ones), I hypothesize that evolutionary and diversity patterns in brooders will be strongly structured in space and time allowing to pinpoint key events with more accuracy. I then use the construction of time-calibrated phylogenies to determine timings of diversification and the influence of historical events, thus improving our knowledge of asteroid evolutionary history. This chapter is based on the analyses of 1,416 genetic sequences of the mitochondrial markers COI.

The third and final chapter is an exploratory approach of the diversity and origin of Southern Ocean sea stars. In chapter 3, the geographical scale is widened at its maximum to explore the roots and evolution of the entire class around the Antarctic continent. I hypothesise that species richness is overlooked and misunderstood in the Southern Ocean due to the origin and evolution of its fauna. This chapter is based on the use of an extensive barcode library compiled from all openly available sequences and the one obtained during this thesis.

Southern Ocean species list update

Southern Ocean Asteroidea: a proposed update for the Register of

Antarctic Marine Species

INTRODUCTION The Register of Antarctic Marine Species, RAMS

RAMS is a collaborative and dynamic information system managing Southern Ocean marine taxon names and related information [START_REF] Jossart | The Register of Antarctic Marine Species (RAMS): a ten-year appraisal[END_REF]. The main objective of RAMS is to establish a benchmark of the present taxonomic knowledge of the Southern Ocean biodiversity [START_REF] De Broyer | How many species in the Southern Ocean? Towards a dynamic inventory of the Antarctic marine species[END_REF].

In a recent appraisal of RAMS, [START_REF] Jossart | The Register of Antarctic Marine Species (RAMS): a ten-year appraisal[END_REF] underscored the number of 10,294 described species of which 8,297 are accepted marine species (viz. checked by taxonomic experts). Among these species, 537 (~6.5%) were reported as accepted species names for echinoderms and 198 (~2.4%) as accepted names for sea star species.

After 10 years of service, RAMS still displays several spatial gaps, especially with regards to species occurring in the sub-Antarctic zone, described as the area below the sub-Tropical front (Deacon 1984[START_REF] Rintoul | Antarctic Circumpolar Current. Encyclopedia of the Antarctic[END_REF] and North of the Polar Front.

In order to complete the taxonomic information for the class Asteroidea, we propose in this work an updated version of the checklist of Southern Ocean sea stars species occurring within the RAMS area of interest.

MATERIALS AND METHODS

Area of interest

As described in De Broyer and Danis (2011) the RAMS area of interest is extending from the coast of the Antarctic continent to the sub-Tropical front. Convenient operational limits have been defined (Table 1; Figure 20), splitting the Southern Ocean into two zones: the Antarctic zone and the sub-Antarctic zone. Table 1 RAMS area of interest. Operational northern limits in the different sector of the Southern Ocean for both the Antarctic zone and the sub-Antarctic zone.

Sector

Longitude range Northern limit

Antarctic zone

South Atlantic Sector 60°W-50°W 57°S 50°W-30°E 50°S Indian Sector 30°E-80°E 50°S 80°E-150°E 55°S South Pacific Sector 150°E-60°W 60°S Sub-Antarctic zone Atlantic & Indian Sectors 60°W-140°E 43°S South Pacific Sector 140°E-176°W 48°S 176°W-80°W 45°S 80°W-72°W 41°S

Data collection

More than 13,000 occurrences records were aggregated from different sources including global information systems such as the Ocean Biogeographic Information System (OBIS), the Global Biodiversity Information Facility (GBIF), initiatives such as the Biogeographic Atlas of the Southern Ocean (De Broyer et al. 2014), historic records mined from the literature pertaining to the early exploration of the Southern Ocean (e.g. Sladen 1889), recently published checklists (e.g. [START_REF] Gutt | Asteroids, ophiuroids and holothurians from the southeastern Weddell Sea (Southern Ocean)[END_REF] or unpublished cruise records. Only the specimens identified at a species level, regardless of their depth (shelf, slope, deep-sea) were kept for the preparation of this checklist.

The validity of each species name was controlled using the Taxa Match Tool available in RAMS (http://www.marinespecies.org/rams/aphia.php?p=match) and WoRMS (http:// www.marinespecies.org/aphia.php?p=match) to ensure its validity and presence in the RAMS checklist.

DATA RESOURCES

Complete checklist of Southern Ocean Asteroidea

The data underpinning the analyses reported in this paper are deposited at GBIF, the Global Biodiversity Information Facility, http://ipt.pensoft.net/resource?r=southern_ocean_asteroidea&v=1.1

Checklist of RAMS Asteroidea species

Abyssaster diadematus (Sladen, 1883); Abyssaster planus (Sladen, 1883); Acodontaster capitatus [START_REF] Koehler | Echinodermes (Astéries, Ophiures et Echinides)[END_REF]; Acodontaster conspicuus [START_REF] Koehler | Echinodermata: Asteroidea. Scientific Reports[END_REF]; Acodontaster elongatus [START_REF] Sladen | Report on the scientific results of the voyage of HMS Challenger during the years 1873-76[END_REF]; Acodontaster hodgsoni (Bell, 1908); Acodontaster marginatus [START_REF] Koehler | Echinodermes (Astéries, Ophiures et Echinides)[END_REF];

Adelasterias papillosa (Koehler, 1906); Allostichaster capensis (Perrier, 1875); Anasterias antarctica (Lütken, 1857); Anasterias asterinoides Perrier, 1875; Anasterias directa [START_REF] Koehler | Echinodermata: Asteroidea. Scientific Reports[END_REF] Anasterias mawsoni [START_REF] Koehler | Echinodermata: Asteroidea. Scientific Reports[END_REF]; Anasterias pedicellaris [START_REF] Koehler | Astéries et Ophiures. Further zoological results of the Swedish Antarctic[END_REF]Anasterias perrieri (E. A. Smith, 1876); Anasterias rupicola (Verrill, 1876); Anasterias sphoerulata [START_REF] Koehler | Echinodermata: Asteroidea. Scientific Reports[END_REF]; Anasterias spirabilis [START_REF] Bell | Contributions to the Systematic Arrangement of the Asteroidea. The Species of the genus Asterias[END_REF] (Koehler, 1906); Ctenodiscus australis Lütken, 1871; Ctenodiscus procurator Sladen, 1889; Cuenotaster involutus [START_REF] Koehler | Echinodermes (Astéries, Ophiures et Echinides)[END_REF]; Cycethra frigida [START_REF] Koehler | Echinodermes (Astéries, Ophiures et Echinides) recueillis par M. Rallier du Baty, aux Iles de Kerguelen, en 1913-1914[END_REF]; Cycethra macquariensis [START_REF] Koehler | Echinodermata: Asteroidea. Scientific Reports[END_REF]Cycethra verrucosa (Philippi, 1857); Diplasterias brandti [START_REF] Bell | Contributions to the Systematic Arrangement of the Asteroidea. The Species of the genus Asterias[END_REF]; Diplasterias brucei [START_REF] Koehler | Astéries, Ophiures et Echinides de l'Expédition Antarctique Nationale Écossaise[END_REF]; Diplasterias kerguelenensis [START_REF] Koehler | Echinodermes (Astéries, Ophiures et Echinides) recueillis par M. Rallier du Baty, aux Iles de Kerguelen, en 1913-1914[END_REF]; Diplasterias meridionalis (Perrier, 1875); Diplasterias octoradiata (Studer, 1885); Diplasterias radiata [START_REF] Koehler | Astéries et Ophiures. Further zoological results of the Swedish Antarctic[END_REF]; Diplodontias singularis (Müller & Troschel, 1843); Diplopteraster clarki Bernasconi, 1937; Diplopteraster peregrinator [START_REF] Sladen | The Asteroidea of HMS Challenger Expedition. (Preliminary notices). 1. Pterasteridae[END_REF]; Diplopteraster semireticulatus [START_REF] Sladen | The Asteroidea of HMS Challenger Expedition. (Preliminary notices). 1. Pterasteridae[END_REF]; Diplopteraster verrucosus [START_REF] Sladen | The Asteroidea of HMS Challenger Expedition. (Preliminary notices). 1. Pterasteridae[END_REF]; Dytaster felix [START_REF] Koehler | Astéries, Ophiures et Echinides recueillis dans les mers australes par la Scotia (1902-1904)[END_REF]Echinaster smithi Ludwig, 1903; Eremicaster crassus (Sladen, 1883); Eremicaster pacificus (Ludwig, 1905); Eremicaster vicinus Ludwig, 1907; Freyastera tuberculata [START_REF] Sladen | Report on the scientific results of the voyage of HMS Challenger during the years 1873-76[END_REF] [START_REF] Koehler | Echinodermata: Asteroidea. Scientific Reports[END_REF]; Lysasterias belgicae [START_REF] Ludwig | Seesterne. Résultats du voyage du S[END_REF]; Lysasterias chirophora [START_REF] Ludwig | Seesterne. Résultats du voyage du S[END_REF]; Lysasterias digitata A.M. [START_REF] Clark | BANZ Antarctic Research Expedition[END_REF]Lysasterias hemiora Fisher, 1940;Lysasterias heteractis Fisher, 1940; Lysasterias joffrei [START_REF] Koehler | Echinodermata: Asteroidea. Scientific Reports[END_REF]; Lysasterias lactea [START_REF] Ludwig | Seesterne. Résultats du voyage du S[END_REF]; Lysasterias perrieri (Studer, 1885);

Macroptychaster accrescens [START_REF] Koehler | Echinodermata: Asteroidea. Scientific Reports[END_REF]; Mediaster pedicellaris (Perrier, 1881);

Mirastrella biradialis [START_REF] Fisher | Asteroidea[END_REF]Neosmilaster georgianus (Studer, 1885); Neosmilaster steineni (Studer, 1885); Notasterias armata (Koehler, 1911); Notasterias bongraini [START_REF] Koehler | Echinodermes (Astéries, Ophiures et Echinides)[END_REF]; Notasterias candicans [START_REF] Ludwig | Seesterne. Résultats du voyage du S[END_REF]; Notasterias haswelli [START_REF] Koehler | Echinodermata: Asteroidea. Scientific Reports[END_REF]; Notasterias pedicellaris [START_REF] Koehler | Astéries, Ophiures et Echinides recueillis dans les mers australes par la Scotia (1902-1904)[END_REF]; Notasterias stolophora [START_REF] Fisher | Asteroidea[END_REF]; Notioceramus anomalus [START_REF] Fisher | Asteroidea[END_REF]; Novodinia novaezelandiae (H.E.S. [START_REF] Clark | BANZ Antarctic Research Expedition[END_REF]; Odinella nutrix [START_REF] Fisher | Asteroidea[END_REF];

Odontaster meridionalis (E. A. Smith, 1876); Odontaster penicillatus (Philippi, 1870);

Odontaster pusillus [START_REF] Koehler | Astéries, Ophiures et Echinides recueillis dans les mers australes par la Scotia (1902-1904)[END_REF]Odontaster validus Koehler, 1906; Paralophaster antarcticus [START_REF] Koehler | Echinodermes (Astéries, Ophiures et Echinides)[END_REF]; Paralophaster godfroyi [START_REF] Koehler | Echinodermes (Astéries, Ophiures et Echinides)[END_REF]; Paralophaster lorioli [START_REF] Koehler | Astéries, Ophiures et Echinides recueillis dans les mers australes par la Scotia (1902-1904)[END_REF]; Pectinaster filholi Perrier, 1885; Pedicellaster hypernotius Sladen, 1889;

Pergamaster incertus (Bell, 1908); Pergamaster triseriatus H.E.S. Clark, 1963; Peribolaster folliculatus Sladen, 1889; Peribolaster macleani [START_REF] Koehler | Echinodermata: Asteroidea. Scientific Reports[END_REF]; Perknaster antarcticus (Koehler, 1906); Perknaster aurantiacus [START_REF] Koehler | Echinodermes (Astéries, Ophiures et Echinides)[END_REF]; Perknaster aurorae [START_REF] Koehler | Echinodermata: Asteroidea. Scientific Reports[END_REF];

Perknaster charcoti [START_REF] Koehler | Echinodermes (Astéries, Ophiures et Echinides)[END_REF] After a careful verification of the RAMS species list for Asteroidea we propose to address the following points. These issues have been taken into account in this paper:

• Cheiraster (Barbadosaster) echinulatus and Stegnaster wesseli are only described from Central America and should be removed from the RAMS list

• Spoladaster veneris is only described from Amsterdam and Saint-Paul Islands which are not part of the RAMS area of interest

• Anthenoides peircei, Astropecten cingulatus, Cheiraster (Cheiraster) sepitus, Peltaster placenta, and Psilaster herwigi do not seem to be distributed in the RAMS area of interest

• Echinaster (Othilia) brasiliensis is only described from South America and should be removed of the RAMS list

• Freyella mutabilia was originally described as Freyella mutabila by [START_REF] Korovchinsky | New species of abyssal starfishes of the genus Freyella (Brisingidae) from the South Atlantic[END_REF] • Mimastrella cognata and Mirastrella cognata are source of a problem. Both genera do exist but Mimastrella cognata and Mirastrella biradialis are the only described species. The genus name being nearly identical, it has led to a mistake. Mirastrella cognata is an invalid name and should be deleted from RAMS and WoRMS systems.

Moreover, we recommend the addition of species from our "Proposed-RAMS" checklist (i.e.

species not registered in the RAMS list but present in the RAMS area of interest) to RAMS.

None of these species are new to science but their austral distribution range was not properly documented (e.g. species from the Campbell Plateau are reported as New-Zealand species but are also present in the Southern Ocean, species from the French sub-Antarctic Islands, etc...).

Interestingly, 22 of the 97 "non-RAMS" species are present in the Antarctic zone. Some have been described recently (e.g. O. roseus and O. pearsei described by [START_REF] Janosik | Unrecognized Antarctic biodiversity: a case study of the genus Odontaster (Odontasteridae; Asteroidea)[END_REF]; C. trangae described by [START_REF] Mah | Taxonomy of high-latitude Goniasteridae (Subantarctic & Antarctic): one new genus, and three new species with an overview and key to taxa[END_REF] or P. tyleri described by [START_REF] Mah | Description of a new family, new genus, and two new species of deep-sea Forcipulatacea (Asteroidea), including the first known sea star from hydrothermal vent habitats[END_REF] but have not been added to the RAMS.

A final comment pertains to Astropecten polyacanthus, occurring in the RAMS Sub-Antarctic region in a location that is not actually South from the Sub-Tropical Front. This final observation shows that convenient boundaries should be used with care. However, only one species was concerned for a very wide area of interest. A. polyacanthus presence in the RAMS checklist should be discussed by the editors from RAMS and WoRMS.

DISCUSSION

This study highlights the fact that after ten years of effort, the work is still in progress for RAMS. The main objective of covering the Antarctic zone has generally been reached for the class Asteroidea but needs at this point to go through a major update by the editors. Regarding the asteroids, the secondary objective of covering the Sub-Antarctic zone lacked the impulse of the scientific community and we hope that the work presented here will fill the gaps as accurately as possible.

This approach may not bring the same results for all the taxa in the Southern Ocean. Indeed, some charismatic fauna are very well known in the RAMS area of interest (e.g. marine mammals), however, we believe that the knowledge concerning the number of species present in the Southern Ocean waters might be significantly increased.

Only few mistakes were found in the existing RAMS list of Asteroidea and should be fixed soon after getting in contact with the editors. The new updated checklist of Asteroidea species will be available through the RAMS website (http://www.marinespecies.org/rams) in early 2016.

A way to improve the general system, with the sea stars for model is also in development.

Recent work using genetics on Odontaster species [START_REF] Janosik | Unrecognized Antarctic biodiversity: a case study of the genus Odontaster (Odontasteridae; Asteroidea)[END_REF]) highlights the fact that diversity might be higher than expected even in well-studied areas. There is also a lack of ressources for identification and taxonomic work leading to redundant mistakes. In this context, the creation of a digital library, hotlinked with the RAMS and compiling original descriptions, literature materials and DNA barcoding information for each species will bring the RAMS a step ahead and provide a vital tool for future taxonomic and biogeographic work.

Perspectives also include an illustrative determination key using a polytomic approach and the creation of interactive Antarctic Field Guides (http://afg.biodiversity.aq) on the http://www.biodiversity.aq platform (Van de [START_REF] Van De Putte | The Antarctic Biodiversity Information Facility[END_REF] in order to help the scientific community with the identification process and to enhance data availability.

We believe that the homogenization of available data for all taxa will result in a better understanding of the Southern Ocean and its biogeography, especially in the Sub-Antarctic zone.

Asteroidea Database

Antarctic and Sub-Antarctic Asteroidea database This extensive assessment was pursued by major improvements in methodologies and data analyses. Improvement of dataset completeness and resolution facilitates modelling approaches [START_REF] Gutt | Correlative and dynamic species distribution modelling for ecological predictions in the Antarctic: a cross-disciplinary concept[END_REF] that provide interesting tools to better understand distribution patterns in this poorly documented part of the world.

Among benthic taxonomic groups, Asteroidea (Echinodermata) are well represented in the Southern Ocean with 12% of the global species richness present in the region [START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF]. Around 300 species [START_REF] Moreau | Southern Ocean Asteroidea: a proposed update for the Register of Antarctic Marine Species[END_REF] were reported at all depths including some potential keystone species in benthic communities [START_REF] Mcclintock | Population structure and energetics of the shallow-water Antarctic sea star Odontaster validus in contrasting habitats[END_REF](McClintock et al., , 2008)). As for many taxonomic groups, adaptations of invertebrates to the polar conditions of the Southern Ocean environments have been widely reported [START_REF] Peck | Ecophysiology of Antarctic marine ectotherms: limits to life[END_REF][START_REF] Peck | A cold limit to adaptation in the sea[END_REF] and have led to unique biological traits and life-strategies as well as high levels of endemism in the region [START_REF] Chown | The changing form of Antarctic biodiversity[END_REF].

In particular, reproductive strategies are diversified in the Southern Ocean with a distinction between brooding and broadcasting species [START_REF] Poulin | Evolutionary versus ecological success in Antarctic benthic invertebrates[END_REF][START_REF] Pearse | Brooding and species diversity in the Southern Ocean: selection for brooders or speciation within brooding clades? Smithsonian at the poles: contributions to international polar year science[END_REF]. In asteroids, the two distinct reproductive strategies strongly drive species distribution patterns and the biogeography of the class in the Southern Ocean [START_REF] Moreau | Reproductive strategy as a piece of the biogeographic puzzle: a case study using Antarctic sea stars (Echinodermata, Asteroidea)[END_REF].

Study area descriptions / descriptor:

This study focuses on the Antarctic and Sub-Antarctic regions located at latitudes south of 45°S. The Southern Ocean is a vast region characterised by the paucity of its scientific data [START_REF] Griffiths | Antarctic marine biodiversity -what do we know about the distribution of life in the Southern Ocean?[END_REF][START_REF] Griffiths | Quantifying Antarctic marine biodiversity: The SCAR-MarBIN data portal[END_REF] and available collections are the compilation of several historical campaigns. The objective of this work is to integrate the most complete database of species occurrences for the class Asteroidea in the described geographic extent.

Design description:

The compilation of occurrence data of asteroid species over the extent of the Southern Ocean was realised by gathering data available from various biodiversity information systems (OBIS, GBIF, biodiversity.aq, PANGAEA https://www.pangaea.de/) as well as published literature, including original manuscripts (e.g., [START_REF] Gutt | Asteroids, ophiuroids and holothurians from the southeastern Weddell Sea (Southern Ocean)[END_REF][START_REF] Moles | Distribution patterns in Antarctic and Subantarctic echinoderms[END_REF], data papers and cruise reports. Data description: Asteroids are common invertebrates of Antarctic benthic communities considering the relative high species richness of the group in the region with regards to the world total diversity (Danis et al., 2014). They play a significant ecological role in Antarctic ecosystems, including in trophic networks (most species being predators) [START_REF] Dayton | Toward an understanding of community resilience and the potential effects of enrichments to the benthos at McMurdo Sound, Antarctica[END_REF][START_REF] Lawrence | Starfish: biology and ecology of the Asteroidea[END_REF]. The present dataset, that focuses on regions located at latitudes higher than 45°S, compiles 28 families out of the 39 known worldwide [START_REF] Linchangco | The phylogeny of extant starfish (Asteroidea: Echinodermata) including Xyloplax, based on comparative transcriptomics[END_REF]

Taxonomic coverage

General taxonomic coverage description

The present dataset is the most exhaustive and up-to-date list of available occurrences for the class Asteroidea (Echinodermata), in the entire Southern Ocean. This collection provides information about the occurrence of 28 asteroid families, 118 genera, and 299 species.

Occurrence distribution is illustrated on Figure 1.

Species richness in the different regions of the Southern Ocean was estimated based on 1° × 1° grid cell resolution (Figure 2A). Maximum richness (55 species per cell) was found along the Western Antarctic Peninsula. High richness values were also reported in the Weddell Sea as well as in Sub-Antarctic Islands (Kerguelen, Crozet, Marion, and South Georgia Islands).

Richness distribution needs to be interpreted carefully considering the patchy and uneven sampling effort of past oceanographic cruises carried out in the Southern Ocean (Figure 2B). Hierarchy level: Dataset

INTRODUCTION

The Southern Ocean sensu lato, as defined by oceanographers, includes the marine area south of the Subtropical Front (STF) [START_REF] Longhurst | Ecological geography of the sea[END_REF][START_REF] Rintoul | Antarctic Circumpolar Current. Encyclopedia of the Antarctic[END_REF][START_REF] Post | Environmental Setting. Biogeographic Atlas of the Southern Ocean[END_REF]). In the framework of large-scale biogeographic studies of marine benthic life, the Southern Ocean is generally divided into four major geographic entities (i.e. provinces): the Magellanic Plateau, represented by the southern tip of South America (South Chile, South Argentina, Tierra Del Fuego and the Malvinas/Falkland Islands); Southern New Zealand, represented by the Campbell Plateau; the sub-Antarctic area, located between the STF in the north and the Polar Front in the south, which is mainly composed of abyssal plains and several igneous Islands (e.g. Crozet archipelago, Kerguelen and Heard Islands); and the Antarctic province, defined as the region south of the Polar Front [START_REF] Griffiths | Towards a generalized biogeography of the Southern Ocean benthos[END_REF]. The Antarctic province is one of the most remote places on Earth, despite representing c. 11% of the global continental shelf surface, and surrounded by the Southern Ocean which surface accounts for c. 8% of all the world's oceans [START_REF] Griffiths | Antarctic marine biodiversity -what do we know about the distribution of life in the Southern Ocean?[END_REF][START_REF] Ingels | Possible effects of global environmental changes on Antarctic benthos: a synthesis across five major taxa[END_REF]. Each of these provinces can then be divided into smaller entities, defined as bioregions (cf. [START_REF] Hedgpeth | Introduction to Antarctic zoogeography. Distribution of selected groups of marine invertebrates in water south of 35[END_REF].

The long-term faunal connections within and among these four provinces cannot be explained by a "one-size fits-all" biogeographic theory. Indeed, biogeographic patterns appear to be dependent upon the taxon investigated (e.g. Barnes & Griffiths, 2007 for Bryozoa; [START_REF] Linse | Biodiversity and biogeography of Antarctic and sub-Antarctic mollusca[END_REF]Barnes & Griffiths, 2007;[START_REF] Downey | Diversity and distribution patterns in high southern latitude sponges[END_REF][START_REF] Pierrat | Comparative biogeography of echinoids, bivalves and gastropods from the Southern Ocean[END_REF].

Oceanographic features which are unique to the Southern Ocean, such as the Polar Front, act as a barrier between polar and sub-Antarctic water masses. Both water masses show contrasting physico-chemical properties, and the Polar Front creates a steep gradient in temperature and salinity [START_REF] Venables | Fronts and habitat zones in the Scotia Sea[END_REF]. Geomorphological features, such as a "belt" the entire Antarctic continent [START_REF] Pearse | Brooding and species diversity in the Southern Ocean: selection for brooders or speciation within brooding clades? Smithsonian at the poles: contributions to international polar year science[END_REF][START_REF] Pierrat | Comparative biogeography of echinoids, bivalves and gastropods from the Southern Ocean[END_REF]David & Saucède, 2015).

Regional-scale processes may also shape biogeographic patterns. For instance, the Polar Front has "marine corridors" connecting distinct regions [START_REF] Clarke | How isolated is Antarctica?[END_REF][START_REF] Barnes | Antarctic marine biology[END_REF]. Other oceanographic features, such as regional-scale eddies, island archipelagos, seamounts or refugia during glacial cycles may also have influenced the distribution of benthic species (e.g. [START_REF] Barnes | Bryozoans of the Weddell Sea continental shelf, slope and abyss: did marine life colonize the Antarctic shelf from deep water, outlying islands or in situ refugia following glaciations?[END_REF] for pycnogonids, 87% for isopods, 81% for tanaids, 51% for ascidians and 80% for cumaceans.

Sea stars (Asteroidea, Echinodermata) are common organisms living on the Antarctic seafloor with specimens found in diverse environments [START_REF] Brandt | First insights into the biodiversity and biogeography of the Southern Ocean deep sea[END_REF]Linse et al., 2007a;[START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF]. High latitude asteroids have been studied since the late 19th century in the Southern Ocean (e.g. [START_REF] Sladen | Report on the scientific results of the voyage of HMS Challenger during the years 1873-76[END_REF] with hundreds of species recorded (latest checklist in [START_REF] Moreau | Southern Ocean Asteroidea: a proposed update for the Register of Antarctic Marine Species[END_REF] and frequent checklists (e.g. [START_REF] Moles | Distribution patterns in Antarctic and Subantarctic echinoderms[END_REF]. Moreover, there is a particularly high proportion of brooding sea stars in the Southern Ocean [START_REF] Poulin | Evolutionary versus ecological success in Antarctic benthic invertebrates[END_REF][START_REF] Pearse | Brooding and species diversity in the Southern Ocean: selection for brooders or speciation within brooding clades? Smithsonian at the poles: contributions to international polar year science[END_REF]. Despite the potential importance of asteroids as ecosystem structuring agents [START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF][START_REF] Lawrence | Starfish: biology and ecology of the Asteroidea[END_REF], very few studies have assessed the overall distribution pattern of Southern Ocean asteroid diversity (Danis et al., 2014;[START_REF] Moles | Distribution patterns in Antarctic and Subantarctic echinoderms[END_REF] and the relative importance of each driving factor involved in the observed patterns

has not yet been addressed.

In a recent update of the Register of Antarctic Marine species (RAMS), [START_REF] Moreau | Southern Ocean Asteroidea: a proposed update for the Register of Antarctic Marine Species[END_REF] reported a total of 295 species, representing more than 15% of the nearly 1,900 extant species of asteroids [START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF]. Initiatives such as RAMS and the World Register of Marine Species (WoRMS Editorial Board, 2015) enable the use of global data systems [e.g.

Ocean Biogeographic Information System (OBIS -http:// www.iobis.org/), Global Biodiversity Information Facility (GBIF -http://www.gbif.org/)] to compile hundreds of thousands georeferenced data entries [START_REF] Costello | Global coordination and standardisation in marine biodiversity through the World Register of Marine Species (WoRMS) and related databases[END_REF][START_REF] Jossart | The Register of Antarctic Marine Species (RAMS): a ten-year appraisal[END_REF]. Such extensive datasets can be used to address key biological questions, such as the origin and the structure of asteroid biogeographic patterns in the Southern Ocean.

The objectives of this work were to describe and analyse asteroid biogeographic patterns in the Southern Ocean and test whether reproductive strategy (brooder versus broadcaster) can explain distribution patterns. Specifically, we hypothesise that the contrasting ability of asteroids to disperse (short range for brooders and long range for broadcasters) will generate contrasting biogeographic patterns.

MATERIALS AND METHODS

Area of interest

The geographic area investigated in this study focuses on the Southern Ocean, at latitudes higher than 45°S (Figure 23). The Southern Ocean was then subdivided into the following 25 bioregions based on several recent biogeographic studies [START_REF] Linse | Biodiversity and biogeography of Antarctic and sub-Antarctic mollusca[END_REF][START_REF] Clarke | How well do we know the Antarctic marine fauna? A preliminary study of macroecological and biogeographical patterns in Southern Ocean gastropod and bivalve molluscs[END_REF][START_REF] Spalding | Marine ecoregions of the world: a bioregionalization of coastal and shelf areas[END_REF][START_REF] Pierrat | Comparative biogeography of echinoids, bivalves and gastropods from the Southern Ocean[END_REF][START_REF] De Broyer | Biogeographic patterns of Southern Ocean benthic Amphipods. Biogeographic Atlas of the Southern Ocean[END_REF] and to take into account all occurrences data available for the Southern Ocean asteroids (see

Data analyses

Cleaned data (See Appendix 1) were compiled into a matrix providing information for each species on the bioregion and depth of occurrence. The dataset was used in its entirety for richness analyses. For biogeographic analyses, occurrences from depths lower than 1,500 m (abyssal domain and beyond) were excluded to only focus on shelf areas and on the upper slope. This depth range also includes shallow canyons and troughs. The main changes in faunal communities of the Southern Ocean occur at around 1,500 m depth, deeper than elsewhere in the world's oceans [START_REF] Brandt | Southern Ocean benthic deep-sea biodiversity and biogeography. Biogeographic Atlas of the Southern Ocean[END_REF]. Bathymetric data were compiled using the GEBCO (2014) grid (www.gebco.net). Analyses were performed at the genus and species levels. At the species level, brooding and broadcasting species were also investigated separately to test our working hypothesis (see Appendix 1 for sources regarding the reproductive strategy). Species accumulation curves were calculated to test the consistency of richness estimation using PRIMER 6 [START_REF] Clarke | User manual/tutorial[END_REF] with a focus on the first 250 stations (Figure 24a).

Three complementary approaches were used to quantitatively investigate faunal similarities between the 25 bioregions. Two multivariate analyses, non-metrical multidimensional scaling (nMDS) and clustering, were carried out using PRIMER 6 [START_REF] Clarke | User manual/tutorial[END_REF]) and the Bray-Curtis coefficient [START_REF] Bray | An ordination of the upland forest communities of southern Wisconsin[END_REF]. A similarity percentage (SP) is given by the cluster analyses to measure similarities among bioregions or groups of bioregions. We also used the bootstrap spanning network (BSN) procedure to visualise nonmetric inter-assemblages similarity structure as a connected network. BSN allows the simultaneous identification of partially or totally nested patterns as well as gradational linear or reticulated biogeographic structures (see detailed description in [START_REF] Brayard | The biogeography of Early Triassic ammonoid faunas: clusters, gradients and networks[END_REF][START_REF] Brayard | Smithian and Spathian (Early Triassic) ammonoid assemblages from terranes: paleoceanographic and paleogeographic implications[END_REF].

These three methods can be used to identify transitional areas between bioregions and groups of bioregions in term of faunal similarities.

A dissimilarity matrix was calculated using the Bray-Curtis coefficient [START_REF] Bray | An ordination of the upland forest communities of southern Wisconsin[END_REF]. Following the BSN procedure (see [START_REF] Brayard | The biogeography of Early Triassic ammonoid faunas: clusters, gradients and networks[END_REF], similarity relationships were displayed as a connected network directly superimposed on geographic maps. Nodes of the network represent studied bioregions and the robustness of each BSN link between nodes was evaluated by bootstrap replications (10,000 replicates were computed here). A bootstrap support values (BSV: i.e. a confidence interval) is obtained for each link between bioregions (see [START_REF] Brayard | The biogeography of Early Triassic ammonoid faunas: clusters, gradients and networks[END_REF]Brayard et al., , 2009 for details) for details). When superimposed on geographic maps, the BSN provides an intuitive visualisation, as well as a quantitative appraisal of faunal exchange pathways and biogeographic structures. BSNs were created with the software BSN 1.0 [START_REF] Brayard | The biogeography of Early Triassic ammonoid faunas: clusters, gradients and networks[END_REF] and visualisations were created in PAJEK 1.07 [START_REF] Batagelj | Pajek (program for analysis and visualization of large network)[END_REF].

In order to quantitatively compare BSN among different taxonomic levels and reproductive strategies, we built a triangular matrix by multiplying the BSV between bioregions for each of our four studied situations (genus level, species level, brooding and broadcasting species).

When two or more pathways were possible in the BSN, we kept the smallest value in order to reflect the highest similarity relationship. The bioregions Bount&Ant, Cam&Auc, AS&BS and Mac were removed from correlation analyses because they were rarely connected to other bioregions in the BSN analyses. A Mantel test using the Spearman coefficient was used to measure correlations between the BSN structures. Finally, endemism levels of asteroid species were analysed by comparing the Southern Ocean area dataset and the OBIS/GBIF occurrences for the rest of the world. Endemism within each bioregion was also quantified.

RESULTS

Sampling effort, richness patterns and endemism

There are clear differences in sampling effort intensity among the bioregions, ranging The steepest curves, reflecting potential high species richness, are all found in the area between South America and the Antarctic Continent (TdF, SG&Sha, SSand, SOrk, AP&SSh and WS). Our final dataset contained 14,005 occurrence records, accounting for 4,512 stations. All seven orders of the class Asteroidea were represented, including 299 species assigned to 28 families and 118 genera (Table 2).

Of the 299 species in the dataset, 196 (c. 66%) also occur south of the Polar Front and 123 species (c. 41%) have distributions that also extend north of the STF. Thus, a total of 176 species (c. 59%) occur exclusively south of the STF and are endemic to the Southern Ocean.

Biogeographic patterns of species

Bioregions are structured into three major groups (Figure 25a

Brooders versus broadcasters

Information about reproductive strategies was available for 59 species with occurrence data shallower than 1,500 m: 37 brooding species (accounting for 2,403 occurrences) and 22 broadcasting species (4,608 occurrences). Cluster analysis of brooding species (Figure 25e) Faunal affinities for broadcasting species (Figure 25g) show higher similarity values than brooders, except for New Zealand (I) which is isolated at 12% of SP. A second group (II)

formed by Antarctic (AS&BS, QML&EL) and South American bioregions (SChi and SArg) is distinguished from the remaining bioregions (III) (SP = 46%) structured into two subgroups (SP = 64%): the sub-Antarctic Islands (IIIa) and Antarctic bioregions with TdF (IIIb). The BSN network for broadcasting species (Figure 25h) highlights the isolation of New Zealand from Southern Ocean bioregions. Sub-Antarctic Islands are all strongly linked to each other and to South America through Tierra del Fuego (TdF) (BSV = 98.8%). Brooder and broadcaster networks (Table 3) were not correlated (rs = 0.296; P = 0.067).

Biogeographic patterns of genera

At genus level, bioregions are structured in three distinct geographic groups (Figure 25c,d): (I) New Zealand (SP = 32%),(II) South America (including TdF) and the sub-Antarctic Islands together, separated from a last group composed of (III) Antarctic bioregions (SP = 55%).

At regional scale, group II can be split into two smaller entities: South America (IIa) and the sub-Antarctic Islands (IIb) (SP = 59%). The structure of Antarctic bioregions follows a more complex pattern of three distinct subgroups (SP = 65 to 70%): Antarctic Islands (IIIa) (Bal&Sco and Bouv), West Antarctic bioregions (IIIb) (SG&Sha, AP&SSh and SOrk) and high Antarctica (IIIc) (Ross, WS, ALand and PBay). BSN connections among these subgroups (Figure 25d) 25d). There is a significant correlation (Table 3) between genus and species networks (rs = 0. 728; P < 0.0005), between genus and brooder networks (rs = 0.641; P = 0<0.0005), and a moderate but significant correlation between the genus and broadcaster networks (rs = 0.444; P = 0.0142).

highlight

DISCUSSION

Main patterns of Southern Ocean asteroid biogeography

At species level, high levels of endemism reflect the isolation of marine biogeographic units due to oceanographic barriers to dispersal or environmental filters. We found low values of endemism for each bioregion when considered in isolation in contrast to the high levels of endemism for the Southern Ocean (59%) and Antarctic region (29%). These levels are similar to those previously reported for the Southern Ocean [START_REF] Moles | Distribution patterns in Antarctic and Subantarctic echinoderms[END_REF] and high compared to other regions, possibly due to the ancient isolation of the Southern Ocean by the Antarctic Circumpolar Current front system associated to speciation and radiation events within Antarctic waters [START_REF] Watling | Antarctica as an evolutionary incubator: evidence from the cladistic biogeography of the amphipod family Iphimediidae[END_REF][START_REF] Lecointre | Is the species flock concept operational? The Antarctic shelf case[END_REF][START_REF] De Broyer | Biogeographic patterns of Southern Ocean benthic Amphipods. Biogeographic Atlas of the Southern Ocean[END_REF].

Our quantitative analyses highlighted the relatively weak biogeographic connectivity of New Zealand to Southern Ocean bioregions at all taxonomic levels and reproductive 1998). Passive transport of adults and juveniles by kelp rafting may explain this affinity [START_REF] Edgar | Dispersal of faunal and oral propagules associated with drifting Macrocystis pyrifera plants[END_REF] as well as a long-distance transport of larvae.

Distribution patterns of asteroids are strongly structured within the Southern Ocean.

Antarctic and sub-Antarctic provinces are well differentiated from each other with bioregions of East and West Antarctica grouped together to the south, bioregions of South America and the sub-Antarctic Islands to the north. Asteroid distribution is therefore strongly structured according to latitude. This may be a result of the Polar Front acting as a biogeographic barrier to the dispersal of asteroids leading to distinct species assemblages between the two provinces. Northern bioregions are clustered together following an additional, longitudinal segregation between South American bioregions to the west and sub-Antarctic islands to the east.

The role of the Polar Front as a barrier to gene flow between Antarctic and sub-Antarctic benthic fauna has been frequently discussed [START_REF] Clarke | How isolated is Antarctica?[END_REF][START_REF] Fraser | Poleward bound: biological impacts of Southern Hemisphere glaciation[END_REF], although it can be relatively permeable to certain species [START_REF] Convey | Exploring biological constraints on the glacial history of Antarctica[END_REF][START_REF] Sands | Against the flow: evidence of multiple recent invasions of warmer continental shelf waters by a Southern Ocean brittle star[END_REF][START_REF] Fraser | Breaking down the barrier: dispersal across the Antarctic Polar Front[END_REF]. This is supported by the BSN analyses where there is no obvious faunal connection between the sub-Antarctic and Antarctic bioregions, but through the Scotia Arc bioregions. This last area constitutes a potential gateway to Antarctica for northern fauna, as demonstrated in previous research (e.g. IBMANT: [START_REF] Arntz | The Magellan-Antarctic connection: links and frontiers at southern high latitudes. Summary review[END_REF]. Explanations for this include the role of mesoscale eddies [START_REF] Glorioso | Mesoscale eddies in the Subantarctic Front-Southwest Atlantic[END_REF][START_REF] Chown | The changing form of Antarctic biodiversity[END_REF] and stepping-stone dispersal through islands of the Scotia Arc (e.g. [START_REF] Tatiàn | Ascidians (Tunicata, Ascidiacea): species distribution along the Scotia Arc[END_REF][START_REF] Fortes | Biogeography and connectivity between western South American and Antarctic marine molluscs[END_REF].

Our results also show faunal affinities between Magellanic and sub-Antarctic assemblages, supporting previous studies on sponges [START_REF] Downey | Diversity and distribution patterns in high southern latitude sponges[END_REF], molluscs [START_REF] Griffiths | Towards a generalized biogeography of the Southern Ocean benthos[END_REF] and echinoids [START_REF] Pierrat | Comparative biogeography of echinoids, bivalves and gastropods from the Southern Ocean[END_REF]. This pattern is probably driven by the westward flowing Antarctic Circumpolar Current allowing long-distance dispersal of propagules (see [START_REF] Waters | Driven by the West Wind Drift? A synthesis of southern temperate marine biogeography, with new directions for dispersalism[END_REF] for discussion).

West and East Antarctica bioregions are well differentiated from each other, confirming previous studies (e.g. [START_REF] Griffiths | Towards a generalized biogeography of the Southern Ocean benthos[END_REF][START_REF] Pierrat | Comparative biogeography of echinoids, bivalves and gastropods from the Southern Ocean[END_REF][START_REF] De Broyer | Biogeographic patterns of Southern Ocean benthic Amphipods. Biogeographic Atlas of the Southern Ocean[END_REF]. Here, the geological/glacial history of Antarctica can be invoked as a possible cause as the Weddell, Amundsen and Ross Seas may have been connected by a trans-Antarctic seaway [START_REF] Lawver | Evolution of Cenozoic seaways in the circum-Antarctic region[END_REF][START_REF] Pollard | Modelling west Antarctic ice sheet growth and collapse through the past five million years[END_REF]) that separated East Antarctica from continental fragments of West Antarctica [START_REF] Linse | Biodiversity and biogeography of Antarctic and sub-Antarctic mollusca[END_REF][START_REF] Pierrat | Comparative biogeography of echinoids, bivalves and gastropods from the Southern Ocean[END_REF]. Molecular studies partially support this hypothesis [START_REF] Strugnell | Persistent genetic signatures of historic climatic events in an Antarctic octopus[END_REF], although data from East Antarctica are needed for confirmation. The east-west pattern may also have originated from the contrasting environmental conditions that prevail between East and West Antarctica (David & Saucède, 2015). The affinity of asteroid faunas between Tierra del Fuego and West Antarctic bioregions is a novel result, highlighting the importance of connections between South America and Antarctica.

West Antarctica is surprisingly rich in asteroid species, even when compared to other well-sampled areas (Table 2; Figure 24). As previously discussed [START_REF] Barnes | Changing chain: past, present and future of the Scotia Arc's and Antarctica's shallow benthic communities[END_REF][START_REF] Barnes | Incursion and excursion of Antarctic biota: past, present and future[END_REF][START_REF] Linse | Is the Scotia Sea a centre of Antarctic marine diversification? Some evidence of cryptic speciation in the circum-Antarctic bivalve Lissarca notorcadensis (Arcoidea: Philobryidae)[END_REF], this can be accounted for by the Antarctic Circumpolar Current hypothesis (see [START_REF] Pearse | Brooding and species diversity in the Southern Ocean: selection for brooders or speciation within brooding clades? Smithsonian at the poles: contributions to international polar year science[END_REF] that suggests that recurrent (but sporadic) transport of brooding species by the Antarctic Circumpolar Current caused their establishment in the Scotia Arc region. The hypothesis predicts the "existence of many species in clades of varied divergence times, at a wide range of depths, but with highest diversity downstream of the Drake Passage (passage between Cape Horn and the Antarctic peninsula), in the Scotia Arc and Weddell Sea" [START_REF] Pearse | Brooding and species diversity in the Southern Ocean: selection for brooders or speciation within brooding clades? Smithsonian at the poles: contributions to international polar year science[END_REF]. Here, the high number of brooding species and strong species:genus ratio in the Scotia Arc area supports this hypothesis.

The importance of reproductive strategies for asteroid biogeography

Pappalardo & Fernández (2014) recently reported a poleward increasing number of direct developers in crustaceans and molluscs. They linked this to low temperatures and food availability in the highest latitudes, emphasising the importance of life-history traits such as larval development in determining patterns of species richness in marine taxa. The high number of brooding asteroid species in the Southern Ocean can also be explained by vicariance and allopatry, and not solely as a consequence of adaptation [START_REF] Poulin | Evolutionary versus ecological success in Antarctic benthic invertebrates[END_REF][START_REF] Pearse | Brooding and species diversity in the Southern Ocean: selection for brooders or speciation within brooding clades? Smithsonian at the poles: contributions to international polar year science[END_REF].

The ecological uniqueness of the New Zealand asteroid fauna can be explained by the geographic position of New Zealand, which limits faunal exchange and larval dispersal to the south. Surprisingly, with only three brooding species reported in New Zealand waters (among which two are found in the Antarctic region), our results show a connection with East Antarctica (Figure 25f). This weak link might be an artefact due to the very small number of species, but could also reflect an existing relationship such as that proposed for cheilostomatid bryozoa [START_REF] Griffiths | Towards a generalized biogeography of the Southern Ocean benthos[END_REF].

The diversity of asteroids from the sub-Antarctic Islands region appears to have been shaped by a complex evolutionary history. Here, reproductive strategy significantly contributes to our understanding of large-scale distribution patterns. Asteroids of the sub-Antarctic Islands show fewer affinities with South American species than with those of both West and East Antarctic regions. The low capacity of brooders to disperse over large distances (around 7,000 km between South America and the sub-Antarctic Islands) partly explains this delineation, given the absence of stepping stones between the sub-Antarctic Islands. In contrast, the high dispersal capacity of broadcasters reduces the impact of geographic isolation on faunal exchange between provinces. In summary, an original fauna evolved in situ around the islands, with some species arriving from South America and others from the Antarctic region. This scenario explains the interrelationships of the fauna of Tierra del Fuego (Figure 25h), which is highly influenced by both South America and the West Antarctic region.

Only brooding species show a clear structuring of Antarctic bioregions. In contrast, broadcasting species show weak spatial structure with a clear circumpolar continuity and no distinct biogeographic boundary.

More information is required to fully understand the role of reproductive strategy in asteroid biogeography. Larval ecology of sea stars in the Southern Ocean takes a variety of different forms [START_REF] Bosch | Developmental types of shallow-water asteroids of McMurdo Sound, Antarctica[END_REF], with planktonic (planktotrophic or lecitotrophic) larvae for broadcasters. The pelagic larval duration may also vary among species, up to 165 days for Odontaster validus [START_REF] Bosch | Developmental types of shallow-water asteroids of McMurdo Sound, Antarctica[END_REF]) which allows a huge potential for longdistance dispersal. Brooding biology also varies with some broods developing within suboral maternal brood chambers and others beginning their development in the stomach pouch [START_REF] Mcclintock | The biochemical composition, energy content, and chemical antifeedant defenses of the common Antarctic Peninsular sea stars Granaster nutrix and Neosmilaster georgianus[END_REF]. Broods can be carried for several months before releasing a fully developed juvenile. So far there has been little research on species in the Southern Ocean [START_REF] Agüera | Parameter estimations of Dynamic Energy Budget (DEB) model over the life history of a key Antarctic species: the Antarctic sea star Odontaster validus Koehler[END_REF], and most of these focus on near-shore shallow-water species. Overall, brooders account for low fecundity, high survival and a limited dispersal capacity. On the contrary, broadcasters have a high fecundity and a low survival rate of their larvae. Another potentially important (and understudied) factor is variation in habitat suitability for larvae along the dispersal routes. Such suitability depends on many factors including diet of larvae, the dynamics of planktonic life [START_REF] Byrne | From pole to pole: the potential for the Arctic seastar Asterias amurensis to invade a warming Southern Ocean[END_REF], substrate availability and biotic interactions (i.e. competition). New modelling techniques based on experimental data (Dynamic Energy Budget -Functional Trait and Distribution Models) are starting to produce insights into these mechanisms, and can even generate predictive scenarios of migration or invasion (e.g. [START_REF] Byrne | From pole to pole: the potential for the Arctic seastar Asterias amurensis to invade a warming Southern Ocean[END_REF].

Across taxonomic levels and time-scales

Analysing biogeographic patterns at high taxonomic levels can bring insights about upstream patterns of distribution and, in particular, the legacy of past processes for presentday biogeography [START_REF] Pierrat | Comparative biogeography of echinoids, bivalves and gastropods from the Southern Ocean[END_REF]. Our genus-level analysis revealed that some Southern Ocean distribution patterns are ancient and probably linked to major processes that occurred in the past. For instance, the Antarctic versus sub-Antarctic pattern is probably due to the long history of isolation of Antarctic waters. The setting up of the Polar Front and of the Antarctic Circumpolar Current in the early Oligocene (30 Ma BP) [START_REF] Lawver | Evolution of Cenozoic seaways in the circum-Antarctic region[END_REF][START_REF] Lawver | Reconstructions of the Southern Ocean and Antarctic regions. Biogeographic Atlas of the Southern Ocean[END_REF] and of other biogeographic barriers resulting from past geological activity were accompanied by vicariant processes. However, the use of molecular markers is needed to build robust phylogenies and increase the accuracy of divergence times between clades to infer the potential impact of past geological events on the evolution of the fauna. At the generic level, the circum East Antarctic versus West Antarctic pattern can be accounted for by the existence of a past trans-Antarctic pathway linking the Weddell and Ross seas [START_REF] Linse | Biodiversity and biogeography of Antarctic and sub-Antarctic mollusca[END_REF][START_REF] Pierrat | Comparative biogeography of echinoids, bivalves and gastropods from the Southern Ocean[END_REF]. The closure of this pathway and the existence of the Weddell Sea Gyre might explain the absence of strong faunal similarities between the Weddell Sea and the close bioregions of East Antarctic at the species level [START_REF] Linse | Biodiversity and biogeography of Antarctic and sub-Antarctic mollusca[END_REF][START_REF] Pierrat | Comparative biogeography of echinoids, bivalves and gastropods from the Southern Ocean[END_REF]. Finally, in contrast to the species-level analysis, dissimilarities between the asteroid genera of Tierra del Fuego and the West Antarctic region might reflect the recent mixing of species between South America and West Antarctica.

Surprisingly, the biogeographic patterns shown for brooding species are very similar to those of all asteroid genera. New Zealand apart, the two patterns fit almost perfectly and are statistically the most similar to each other (Table 3). This may simply illustrate the conservative biogeographic patterns of brooders compared to broadcasters that are able to disperse over long distances, which is supported by the circumpolar patterns shown in many species (35% of the species found south of the Polar Front in this study) from many taxonomic groups. Such an ability to disperse may also explain the counter-intuitive presence of multiple lineages of certain circumpolar broadcasting species at the same locations (see [START_REF] Hemery | Comprehensive sampling reveals circumpolarity and sympatry in seven mitochondrial lineages of the Southern Ocean crinoid species Promachocrinus kerguelensis (Echinodermata)[END_REF]. If broadcasting species were isolated into refugia during glacial maxima, their populations may have evolved independently and merged again after conditions warmed to form the current biogeographic patterns.

CONCLUSIONS

The biogeographic patterns observed for sea stars in the Southern Ocean are consistent with those of other taxonomic groups. Our result highlights the important role of reproductive strategy to understand large-scale spatial patterns of faunal distribution of asteroids. We therefore recommend that, whenever possible, reproductive strategy should be taken into account in large-scale biogeographic studies. Finally, more effort is needed to fill data shortfalls and to date the diverse origins of biogeographic patterns in the Southern Ocean. Using molecular tools in studies of asteroid species with contrasted reproductive strategies should bring new insights and help to gain a comprehensive understanding of historical legacy on present-day biogeography of the Southern Ocean.

INTRODUCTION

The diversity of marine life in the Southern Ocean has long been underestimated and many taxa could be overlooked or misidentified due to the reliance on systematics based solely on morphological characters [START_REF] Gutt | How many macrozoobenthic species might inhabit the Antarctic shelf?[END_REF][START_REF] Clarke | Antarctic marine benthic diversity: patterns and processes[END_REF]. The growing awareness of these issues and the lack of representative sampling [START_REF] Griffiths | Data distribution: Patterns and implications. Biogeographic atlas of the Southern Ocean[END_REF], have prompted Antarctic marine biologists to undertake a series of comprehensive census surveys covering a wide range of taxa in the last two decades. International efforts such as the International Polar

Year (IPY 2007(IPY -2008) ) and the Census of Antarctic Marine Life (CAML 2005-2010) have been the launching pads for a better assessment of Southern Ocean biodiversity and its underlying ecological processes. Recent studies that have applied molecular techniques to these Southern Ocean specimens, exploring diversity, systematics, and phylogeography, have significantly increased our understanding of Antarctic benthic ecosystems (e.g. [START_REF] Sands | Against the flow: evidence of multiple recent invasions of warmer continental shelf waters by a Southern Ocean brittle star[END_REF]. These international Southern Ocean sampling expeditions have achieved several major objectives, such as the creation of a baseline census of biodiversity [START_REF] De Broyer | How many species in the Southern Ocean? Towards a dynamic inventory of the Antarctic marine species[END_REF][START_REF] Griffiths | Quantifying Antarctic marine biodiversity: The SCAR-MarBIN data portal[END_REF], proposing how evolution has been influenced by the regional geological, climatic, and oceanographic histories (e.g. [START_REF] Fraser | Kelp genes reveal effects of subantarctic sea ice during the Last Glacial Maximum[END_REF][START_REF] González-Wevar | Unexpected absence of island endemics: Long-distance dispersal in higher latitude sub-Antarctic Siphonaria (Gastropoda: Euthyneura) species[END_REF], and disentangling phylogeographic patterns at lower taxonomic levels to better understand relationships among populations and species on a case by case strategy (e.g. [START_REF] Brasier | Distributional Patterns of Polychaetes Across the West Antarctic Based on DNA Barcoding and Particle Tracking Analyses[END_REF][START_REF] Dömel | Nuclear and mitochondrial gene data support recent radiation within the sea spider species complex Pallenopsis patagonica[END_REF]. This extensive work led to the discovery and the description of many new species (e.g. [START_REF] Janosik | Unrecognized Antarctic biodiversity: a case study of the genus Odontaster (Odontasteridae; Asteroidea)[END_REF]d'Udekem d'Acoz & Verheye, 2017). More importantly, these studies show the frequent discordance existing between traditional (morphology based) and molecular (DNA based) methods for assessing species diversity (e.g. [START_REF] Dömel | Nuclear and mitochondrial gene data support recent radiation within the sea spider species complex Pallenopsis patagonica[END_REF][START_REF] Janosik | Evolutionary history of Southern Ocean Odontaster sea star species (Odontasteridae; Asteroidea)[END_REF]. Cryptic speciation is a documented source of species diversity underestimation, but it is not the only one. A recent study on the most studied sea star species in the Southern Ocean, Odontaster validus, [START_REF] Peck | Morphological variation in taxonomic characters of the Antarctic starfish Odontaster validus[END_REF] showed that polymorphism in some morphological characters could lead to misidentification of this frequently encountered species. Incorrect taxonomic assignments due to the lack of clear identification keys [START_REF] Allcock | Bipolarity. Biogeographic Atlas of the Southern Ocean[END_REF], descriptions of nominal species based on distribution only (Diaz et al. 2011, Saucède et al., 2015), descriptions based on juvenile specimens [START_REF] Roberts | Southern Ocean Pteropods. Biogeographic Atlas of the Southern Ocean[END_REF] or on deteriorated specimens due to inappropriate conservation practices, are all common limitations in meaningful biodiversity assessments [START_REF] Meyer | Limitations in global information on species occurrences[END_REF].

Processes that have and continue to drive complex diversity patterns in the Southern Ocean are far from being fully understood, but the role of certain drivers has been demonstrated in a number of molecular studies. Processes can be extrinsic (e.g. paleogeographic, climatic, oceanographic) or intrinsic (life history traits) (Allcock & Strugnell, 2012;[START_REF] Thatje | Effects of capability for dispersal on the evolution of diversity in Antarctic benthos[END_REF], and their combined effects cumulative, making identification of explanatory processes a difficult endeavour. Life history traits such as reproductive strategies have been proven to shape the genetic structure of species in contrasting ways [START_REF] Modica | Do larval types affect genetic connectivity at sea? Testing hypothesis in two sibling marine gastropods with contrasting larval development[END_REF]. Most marine benthic organisms show low to zero mobility during the adult stage. The dispersal capacity of larvae is thus expected to condition population genetic structure [START_REF] Bowen | Phylogeography of two Atlantic squirrelfishes (Family Holocentridae): exploring links between pelagic larval duration and population connectivity[END_REF][START_REF] Purcell | Weak genetic structure indicates strong dispersal limits: a tale of two coral reef fish[END_REF]. Larval development (e.g. planktotrophic, lecithotrophic), parental care (brooders versus broadcasters) and pelagic larval duration (from days to several months; [START_REF] Selkoe | Marine connectivity: a new look at pelagic larval duration and genetic metrics of dispersal[END_REF], are intrinsic factors that can combine with extrinsic factors, such as oceanographic currents or geological history, to determine the population genetic structure (e.g. [START_REF] Hoffman | Effects of brooding and broadcasting reproductive modes on the population genetic structure of two Antarctic gastropod molluscs[END_REF], Jossart et al., 2017).

As a consequence of their high diversity and differentiated functional roles, benthic invertebrates have been the subject of many studies on genetic diversity and connectivity (see [START_REF] Riesgo | Evolutionary patterns in Antarctic marine invertebrates: An update on molecular studies[END_REF] for a review). Sea stars (Asteroidea, Echinodermata) represent a diversified, abundant and common ecological group in Southern Ocean benthic habitats [START_REF] Jossart | The Register of Antarctic Marine Species (RAMS): a ten-year appraisal[END_REF]. To date, around 300 species have been recorded from the Southern Ocean (Moreau et al., 2015;[START_REF] Moreau | Antarctic and sub-Antarctic Asteroidea database[END_REF] but it is likely that many more remain to be described. Recent studies based on species morphological identification tried to disentangle distribution patterns and biogeographic relationships in sea stars at the scale of the entire Southern Ocean [START_REF] Moles | Distribution patterns in Antarctic and Subantarctic echinoderms[END_REF][START_REF] Moreau | Reproductive strategy as a piece of the biogeographic puzzle: a case study using Antarctic sea stars (Echinodermata, Asteroidea)[END_REF]. These studies described the spatial structure of asteroid assemblages and stressed the major influence of life history traits, among which reproductive strategy appeared to have the most notable effect [START_REF] Moreau | Reproductive strategy as a piece of the biogeographic puzzle: a case study using Antarctic sea stars (Echinodermata, Asteroidea)[END_REF].

Few molecular studies have been performed on Southern Ocean asteroids and they are nearly exclusively focused on the common Odontaster genus (Janosik & Hallanych, 2010;[START_REF] Janosik | Evolutionary history of Southern Ocean Odontaster sea star species (Odontasteridae; Asteroidea)[END_REF]. The phylogeny and evolutionary history of the Asteroidea in the Southern Ocean has, however, been discussed in several studies (Mah & Foltz, 2011a, 2011b, 2014;[START_REF] Mah | Description of a new family, new genus, and two new species of deep-sea Forcipulatacea (Asteroidea), including the first known sea star from hydrothermal vent habitats[END_REF]. In their comprehensive studies on the molecular phylogeny of the superorders Valvatacea and Forcipulatacea, Mah & Foltz (2011a, b) describe some diversification processes in several Antarctic and sub-Antarctic families (e.g. Odontasteridae, Antarctic Asteriidae) but they did not analyse the lower taxonomic levels (i.e., genera and species).

Brooders and broadcasters have contrasting dispersal capabilities (low range dispersal in brooders vs high range in broadcasters) and brooding taxa are usually hypothesised to display 1) higher genetic diversity, 2) greater species richness and 3) more genetic differentiation through space than broadcasters (e.g. [START_REF] Modica | Do larval types affect genetic connectivity at sea? Testing hypothesis in two sibling marine gastropods with contrasting larval development[END_REF][START_REF] Purcell | Weak genetic structure indicates strong dispersal limits: a tale of two coral reef fish[END_REF].

In the present study, we tested these assumptions by investigating the genetic diversity and the phylogeography of five widely distributed asteroid genera across the Southern Ocean. We selected genera with contrasting reproductive strategies in two distinct clades: the three brooding genera Diplasterias, Lysasterias, and Notasterias in the monophyletic family Asteriidae [START_REF] Foltz | Combined mitochondrial and nuclear sequences support the monophyly of forcipulatacean sea stars[END_REF]Mah & Foltz, 2011b), and the two broadcasting genera Psilaster and Bathybiaster in a monophyletic group of the family Astropectinidae (Mah & Foltz 2011a[START_REF] Bosch | Developmental types of shallow-water asteroids of McMurdo Sound, Antarctica[END_REF].

MATERIALS AND METHODS

Comprehensive sampling & DNA sequence compilation

Studied specimens were sampled during several expeditions in the Southern Ocean (Figure 27; Appendix 2), all were preserved in 96% ethanol or frozen, and identified at species or genus level (either by Christopher Mah or Camille Moreau). Genomic DNA was extracted using either a salting-out protocol (modified from Sunnucks & Hales, 1996, with larger volumes and incubation at 70°C for 10 minutes to inhibit protein activity after digestion) or QIAGEN DNeasy extraction kits. A fragment (612 nucleotides) of the mitochondrial gene cytochrome c oxidase subunit I (COI) was then amplified using the specific forward primer LCOech1aF1 for the class Asteroidea and the universal HCO2198 Reverse primer [START_REF] Folmer | DNA primers for amplification of mitochondrial cytochrome c oxidase subunit I from diverse metazoan invertebrates[END_REF]. COI sequences amplified using the same primers were also obtained through The Barcode of Life Data System (BOLD, [START_REF] Ratnasingham | BOLD: The Barcode of Life Data System[END_REF] in both public and private datasets, accounting for 460 of the 1,416 sequences analysed in this study (Appendix 2). As the Astropectinidae genera are also recorded outside the Southern Ocean (under different nominal species), all available sequences for these from outside the Southern Ocean were included within this study (Appendix 2). Reverse and forward sequences were edited and assembled using CodonCode Aligner v6.0.2 and translated using the echinoderm mitochondrial genetic code to ensure the absence of a stop codon. Sequences were aligned using the MUSCLE alignment process [START_REF] Edgar | MUSCLE: multiple sequence alignment with high accuracy and high throughput[END_REF]. Base compositional heterogeneity was examined using match-paired tests for symmetry [START_REF] Ababneh | Matched-pairs tests of homogeneity with applications to homologous nucleotide sequences[END_REF] in SeqVis v1.5 [START_REF] Pörtner | Climate-dependent evolution of Antarctic ectotherms: an integrative analysis[END_REF].

Phylogenetic reconstruction

Due to relatively high genetic distances, phylogenetic relationships were reconstructed independently within the Asteriidae and the Astropectinidae. Coscinasterias muricata and Thrissacanthias penicillatus were used as outgroups respectively, following previous phylogenetic studies (Mah & Foltz, 2011a, 2011b). Maximum Likelihood (ML) and Bayesian Analyses (BA) were used to construct the trees using only unique haplotypes. ML reconstructions were generated using a codon partitioned model and the GTR+G substitution model in RAxML v 8.1.2 [START_REF] Stamatakis | RAxML version 8: a tool for phylogenetic analysis and post-analysis of large phylogenies[END_REF] through the RAxMLGUI interface [START_REF] Silvestro | raxmlGUI: a graphical front-end for RAxML[END_REF]. To assess branch support, 10 runs were realised with 1,000 thorough bootstraps each. The PartitionFinder v2 software [START_REF] Lanfear | PartitionFinder 2: new methods for selecting partitioned models of evolution for molecular and morphological phylogenetic analyses[END_REF] was used for the BA reconstructions on the CIPRES Science Gateway [START_REF] Miller | Creating the CIPRES Science Gateway for inference of large phylogenetic trees[END_REF] to select for best-fit partitioning schemes and models of evolution. An XML file was created with BEAUti v1.8.4 [START_REF] Drummond | Bayesian phylogenetics with BEAUti and the BEAST 1.7[END_REF] (http://tree.bio.ed.ac.uk/software/figtree/).

Species delineation

Several single-locus methods of species delineation were used to delineate and explore diversity among the studied genera. Two of these methods, the Generalized Mixed Yule Coalescent (GMYC - [START_REF] Pons | Sequence-based species delimitation for the DNA taxonomy of undescribed insects[END_REF][START_REF] Fujisawa | Delimiting species using single-locus data and the Generalized Mixed Yule Coalescent approach: a revised method and evaluation on simulated data sets[END_REF] and the multi-rate

Poisson Tree Processes (mPTP - [START_REF] Kapli | Multi-rate Poisson tree processes for single-locus species delimitation under maximum likelihood and Markov chain Monte Carlo[END_REF] are tree-based methods requiring an ultrametric tree for the former and a maximum likelihood tree for the latter. Both single (sGMYC) and multiple-threshold (mGMYC) models were investigated using the R package SPLITS [START_REF] Ezard | Splits: species' limits by threshold statistics[END_REF]) and the ultrametric tree was obtained using BEAST during the phylogenetic reconstruction. The online webservice (available at http://mptp.h-its.org) was used for mPTP with the ML tree constructed using RAxML. We also performed a distancebased analysis using the Automatic Barcode Gap Discovery (ABGD - [START_REF] Puillandre | ABGD, Automatic Barcode Gap Discovery for primary species delimitation[END_REF] on the online server (http://wwwabi.snv.jussieu.fr/public/abgd/abgdweb.html) with default settings for the prior range (0.001, 0.1), K80 corrected distances and a value of 1.5 for the relative gap width (X). We also used the newly developed ASAP method (http://wwwabi.snv.jussieu.fr/public/asap/; Puillandre et al., in prep.) with default settings and K80 corrected distances. For subsequent analyses we have selected the method giving the smallest number of delineated entities as recommended to avoid false interpretation [START_REF] Carstens | How to fail at species delimitation[END_REF]. All molecular diversity indexes were calculated using the DNAsp v6 software [START_REF] Rozas | DnaSP 6: DNA sequence polymorphism analysis of large data sets[END_REF] for each previously delineated species. Differences in haplotype and nucleotide diversity between brooders and broadcasters were tested using a Wilcoxon-Mann-Whitney test (R Core Team, 2018). Only calculations for sample sizes ≥25 individuals, were discussed as suggested by [START_REF] Goodall-Copestake | On the comparison of population-level estimates of haplotype and nucleotide diversity: a case study using the gene cox1 in animals[END_REF]. Intra and inter-specific genetic distances within each genus were calculated using MEGA v7.0.18 [START_REF] Kumar | MEGA7: molecular evolutionary genetics analysis version 7.0 for bigger datasets[END_REF] and the Kimura 2-parameter model. Haplotype networks were generated using a TCS network method [START_REF] Clement | TCS: Estimating gene genealogies[END_REF] inferred in the software PopART (http://popart.otago.ac.nz).

The genus Psilaster being recovered as polyphyletic, we focus on the Southern Ocean nominal species Psilaster charcoti.

Phylogenies and divergence time estimates

In total, 578 sequences in broadcasters and 838 in brooders were used for ML and BA reconstructions. Both methods give congruent results for broadcasters with similar taxonomic groupings and high node supports (Figure 28). Node support was higher using the BA method for brooders. Branching patterns were however identical in all reconstructions.

The monophyly of the genus Psilaster is not supported by our analysis but Southern

Ocean Psilaster representatives are monophyletic (i.e. the nominal species P. charcoti). The genus Bathybiaster is monophyletic and includes specimens from the Southern Ocean and from the Northern Hemisphere (Figure 28). In brooders, divergence time estimates (Figure 28; Appendix 2) between East Antarctic subclades and those of the Antarctic Peninsula all fall within the same time range of 2.1 ± 1.2 Ma (Nodes III, V and VI in Figure 28). This is also in line with the time range computed for broadcasters.

Phylogeographic patterns

All brooders display clear geographical patterns, with a distinction between the East Antarctic and the Antarctic Peninsula (Figure 28

DISCUSSION

Species richness, genetic diversity and taxonomic implications

We found that genetic diversity did not significantly differ between brooders and broadcasters. This may reflect the presence of species complexes, related to recurrent disturbances. Recent glacial and interglacial cycles could have promoted high rates of differentiation in Southern Ocean species [START_REF] O'hara | Contrasting processes drive ophiuroid phylodiversity across shallow and deep seafloors[END_REF], regardless of their dispersal capabilities. Discordances between the different delineation methods were detected in all groups. This had already been highlighted in recent studies [START_REF] Kekkonen | Delineating species with DNA barcodes: a case of taxon dependent method performance in moths[END_REF][START_REF] Blair | Cryptic diversity and discordance in single-locus species delimitation methods within horned lizards (Phrynosomatidae: Phrynosoma)[END_REF] and great care should be taken when interpreting the results, as further investigations are needed. At best, these methods should be considered as a first step towards subsequent and more integrative taxonomic works [START_REF] Kekkonen | Delineating species with DNA barcodes: a case of taxon dependent method performance in moths[END_REF] and therefore, a conservative approach is recommended [START_REF] Carstens | How to fail at species delimitation[END_REF]. Genetic diversity among the delineated species falls into the range of intra-specific values obtained in other taxa for COI mtDNA (Goodall-Copestake et al 2012), supporting this approach. Similarly, the measured inter-specific (2-6.8%) distances are within the range obtained in previous studies for sea stars [START_REF] Janosik | Evolutionary history of Southern Ocean Odontaster sea star species (Odontasteridae; Asteroidea)[END_REF][START_REF] Foltz | Global population divergence of the sea star Hippasteria phrygiana corresponds to the onset of the last glacial period of the Pleistocene[END_REF]. DNA barcoding has proven to be an efficient method to differentiate echinoderm species [START_REF] Ward | DNA barcoding discriminates echinoderm species[END_REF] with ~98% of the 191 studied species being distinguished based on their COI barcodes. Rapid diversification can however make intra-and inter-species genetic distances difficult to interpret using species delineation methods. The clear discrepancy between current taxonomy and our results emphasises the urgent need for a complete reassessment of Southern Ocean asteroid taxonomy based on multiple genes and an integrative taxonomic approach at both species and genus levels.

Dispersal capacity and biogeographic patterns

Several mechanisms have been proposed to account for the unusually high proportion of brooding species in the Southern Ocean and the evolutionary success of Antarctic brooders is now widely recognised within the community of Antarctic biologists [START_REF] Poulin | Evolutionary versus ecological success in Antarctic benthic invertebrates[END_REF].

While adaptation to polar environmental conditions is not considered a determining mechanism [START_REF] Poulin | Evolutionary versus ecological success in Antarctic benthic invertebrates[END_REF][START_REF] Pearse | Brooding and species diversity in the Southern Ocean: selection for brooders or speciation within brooding clades? Smithsonian at the poles: contributions to international polar year science[END_REF], reproductive strategy has been hypothesised as the main factor structuring the evolution and the diversity of Southern Ocean benthic life (e.g. [START_REF] Raupach | Genetic homogeneity and circum-Antarctic distribution of two benthic shrimp species of the Southern Ocean, Chorismus antarcticus and Nematocarcinus lanceopes[END_REF][START_REF] Thatje | Effects of capability for dispersal on the evolution of diversity in Antarctic benthos[END_REF]. Whether they are based on morphology (e.g. [START_REF] Moreau | Reproductive strategy as a piece of the biogeographic puzzle: a case study using Antarctic sea stars (Echinodermata, Asteroidea)[END_REF] or genetic markers (e.g. [START_REF] Hoffman | Effects of brooding and broadcasting reproductive modes on the population genetic structure of two Antarctic gastropod molluscs[END_REF], most studies agree that biogeographic structures are more pronounced in brooders than in broadcasters due to contrasting dispersal capacities.

Most of the results obtained in the present study are in line with this expected biogeographic pattern, with the prevalence of clear spatial structures in brooders. This is in agreement with our previous work describing the Southern Ocean asteroid biogeographic patterns and demonstrating the importance of life history traits to understanding the structure of spatial distributions [START_REF] Moreau | Reproductive strategy as a piece of the biogeographic puzzle: a case study using Antarctic sea stars (Echinodermata, Asteroidea)[END_REF]. Our results support the differentiation of species between the Antarctic Peninsula and the East Antarctic. The past collapse of the West Antarctic Ice Sheet [START_REF] Bamber | Reassessment of the potential sea-level rise from a collapse of the West Antarctic Ice Sheet[END_REF][START_REF] Pollard | Modelling west Antarctic ice sheet growth and collapse through the past five million years[END_REF] and the putative existence of a subsequent trans-Antarctic seaway separating the West and the East Antarctic have been proposed as possible mechanisms leading to such patterns [START_REF] Barnes | Faunal evidence for a late Quaternary trans-Antarctic seaway[END_REF][START_REF] Pierrat | Comparative biogeography of echinoids, bivalves and gastropods from the Southern Ocean[END_REF][START_REF] Linse | Biodiversity and biogeography of Antarctic and sub-Antarctic mollusca[END_REF]. The role of the Weddell Sea Gyre [START_REF] Linse | Biodiversity and biogeography of Antarctic and sub-Antarctic mollusca[END_REF], environmental dissimilarities, and contrasting glacial histories have also been proposed as possible explanations [START_REF] Anderson | The Antarctic Ice Sheet during the Last Glacial Maximum and its subsequent retreat history: a review[END_REF]. Interestingly, in brooding genera, haplotypes of specimens from the Weddell Sea are present in both the East Antarctic and the Antarctic Peninsula clades. Recent faunal exchanges between the two regions could explain the occurrence in the Weddell Sea of a mixed fauna of East Antarctic and Antarctic Peninsula origin as the Weddell Sea is located in between these two regions.

Divergence dates suggest that a vicariance event occurred ~2 Myr ago, while the last collapse of the West Antarctic ice sheet is hypothesised to have occurred more recently, in the last 1.1 Myr [START_REF] Pollard | Modelling west Antarctic ice sheet growth and collapse through the past five million years[END_REF][START_REF] Scherer | Antarctic records of precession-paced insolation-driven warming during early Pleistocene Marine Isotope Stage 31[END_REF]. This last dating is in line with previous work on Southern Ocean asteroids [START_REF] Janosik | Evolutionary history of Southern Ocean Odontaster sea star species (Odontasteridae; Asteroidea)[END_REF]. Contrasting divergence dating between phylogeographic studies is not uncommon and absolute ages should be taken with caution when using a molecular clock [START_REF] Thomas | There is no universal molecular clock for invertebrates, but rate variation does not scale with body size[END_REF], given the uncertainties in molecular divergence rates, especially when a single locus is used and when fossil calibrations are not available. However, similar divergence dates were obtained for all brooding genera, which strongly suggests the effect of a common and significant event. Unfortunately, only a few abyssal samples were available for study (only two for the entity Notasterias sp3). They are strongly divergent from all other Notasterias specimens, suggesting the absence of population mixing and independent evolution of populations of Notasterias on both the continental shelf and in the deep-sea.

In contrast to the marked genetic structures described above, exceptions have been in certain brooders due to the effect of unusual dispersal vectors reported [START_REF] Cumming | Transoceanic genetic similarities of kelp-associated sea slug populations: long-distance dispersal via rafting?[END_REF]Dıaz et al., 2011). This is also the case in this study, as the brooding species D. meridionalis shares genetic units between South Georgia and the Kerguelen Islands, which suggests an ongoing connectivity between the two distant regions. This pattern could be explained by kelp rafting via the Antarctic Circumpolar Current, which has previously been found in other Southern Ocean brooding echinoderms (O'Hara, 1998) and taxa such as in isopods and molluscs [START_REF] Leese | Long-distance island hopping without dispersal stages: transportation across major zoogeographic barriers in a Southern Ocean isopod[END_REF][START_REF] González-Wevar | Unexpected absence of island endemics: Long-distance dispersal in higher latitude sub-Antarctic Siphonaria (Gastropoda: Euthyneura) species[END_REF]. Kelp rafting was suggested as a viable dispersal vector for shallow-water species living in macro-algal beds (O'Hara, 1998), which is the case of D. meridionalis.

Genetic structures in broadcasters under study are quite different from the patterns observed in brooders. The studied broadcasters show circumpolar structures that suggest the prevalence of gene flow across the Southern Ocean promoted by higher larval dispersal capacities. Geographic patterns in P. charcoti, with several circumpolar entities, suggest the existence of past refugia during past glacial maxima and subsequent dispersal centres [START_REF] Hemery | Comprehensive sampling reveals circumpolarity and sympatry in seven mitochondrial lineages of the Southern Ocean crinoid species Promachocrinus kerguelensis (Echinodermata)[END_REF]. Unfortunately, little is known about asteroid larval biology in the Southern Ocean, apart from a handful of well-studied species [START_REF] Pearse | Reproduction of Antarctic benthic marine invertebrates: tempos, modes, and timing[END_REF]Agüera et al., 2015;[START_REF] Peck | Juveniles are more resistant to warming than adults in 4 species of Antarctic marine invertebrates[END_REF][START_REF] Souster | Seasonality of oxygen consumption in five common Antarctic benthic marine invertebrates[END_REF]. Major differences exist between the genetic structure of Psilaster and Bathybiaster: (1) clades of P. charcoti are found to have a greatly fragmented pattern, potentially as a result of lower dispersal capacity than representatives of B. loripes (found at continental shelf depths) but this could also reflect a longer evolutionary history as these clades are older (Figure 28), ( 2) some specimens of P. charcoti occur on both sides of the Polar Front and (3) Bathybiaster sp2 shows a potential bipolar distribution (sensu [START_REF] Darling | Molecular evidence for genetic mixing of Arctic and Antarctic subpolar populations of planktonic foraminifers[END_REF] and likely corresponds to the nominal species B. vexillifer. The occurrence of shared haplotypes between the Northern and Southern Hemispheres in Bathybiaster sp2 suggests the existence of recent gene flow between the two hemispheres. Morphological similarities between North American and South African specimens had already been indicated in previous work on the echinoderm fauna of South Africa [START_REF] Clark | The echinoderm fauna of South Africa. Trustees of the South African Museums[END_REF]. This could be the result of a deep-sea dispersal route, a scenario coined the "thermohaline expressway" by [START_REF] Strugnell | The thermohaline expressway: the Southern Ocean as a centre of origin for deep-sea octopuses[END_REF] but a wide, cosmopolitan distribution of the species is probably the most reasonable hypothesis. Unfortunately, no tropical deep-sea samples were available for study.

Bathybiaster sp2 is recorded on the Kerguelen Plateau around the Kerguelen Islands at shallow depths, giving credit to a possible sub-Antarctic emergence scenario and colonisation of the Kerguelen Plateau from the deep sea (Diaz et al., 2011;[START_REF] Aronson | Climate change and invasibility of the Antarctic benthos[END_REF].

Interpretation of the present results is limited by the use of a single mtDNA locus. The observed patterns could be due to mechanisms such as adaptive introgression, demographic disparities or sex-biased asymmetries arising from the sole use of mtDNA [START_REF] Toews | The biogeography of mitochondrial and nuclear discordance in animals[END_REF]. Furthermore, if data derived from COI analyses reflect a long-term effect of contrasting dispersal capacities, other fast evolving nuclear markers such as microsatellites or SNPs (RADseq data) will be needed in the future to investigate these recent and ongoing processes.

Nevertheless, the causal relationship between genetic patterns and dispersal capacities of asteroids, can be linked to past climatic and geological events and give some clues to the upstream drivers of species evolution.

The role of past climate change

The Southern Ocean has been partially isolated for nearly 40 million years since the first opening of the Drake Passage, which led to the onset of the Antarctic Circumpolar Current and subsequent cooling of the ocean when the Antarctic Circumpolar Current intensified.

However, isolation of the Southern Ocean was reduced several times during periods of climate warming and the decreasing Antarctic Circumpolar Current intensity (Lagabrielle et al., 2009;[START_REF] Dalziel | A potential barrier to deep Antarctic circumpolar flow until the late Miocene?[END_REF]. In a recent review of key stages in the evolution of the Antarctic marine fauna, [START_REF] Crame | Key stages in the evolution of the Antarctic marine fauna[END_REF] emphasises the influence of past climate on the current distribution of modern fauna. At the scale of the Cenozoic (c. 65 Myr), he points out that the succession of several major extinction and radiation events are linked to important drops in sea water temperature. The fossil record of Southern Ocean sea stars is very poor but it suggests that the extinction of an older asteroid fauna was followed by the diversification of the Antarctic Asteriidae and of other modern Antarctic forcipulataceans (Mah & Foltz, 2011b). The origin of the Antarctic Asteriidae has been dated to 21 Ma in this study, suggesting a diversification of the family starting in the Miocene after the initial opening of the Drake passage (c. 34 Ma) and before the full establishment of the Antarctic Circumpolar Current (c. 14 Ma) [START_REF] Lawver | Evolution of Cenozoic seaways in the circum-Antarctic region[END_REF]. The global phylogeny of Astropectinidae, reconstructed by Mah & Foltz (2011a), does not show any regional pattern, which makes any speculation as to the origin of Bathybiaster and Psilaster in the Southern Ocean problematic. Our results, however, suggest a recent evolutionary history of broadcasting genera in the Southern Ocean (c. 5 Myr). At a more recent time scale, all the studied groups show a high diversification rate over the last ~2.5 Myr, suggesting that recent climate events could account for these observed patterns.

Naish et al. ( 2009) estimated that at least 38 distinct glacial cycles occurred over the last 5

Myr. These glacial cycles are believed to have been major drivers of species differentiation as hypothesised by the "Antarctic diversity pump" hypothesis [START_REF] Clarke | The origin of the Southern Ocean marine fauna[END_REF][START_REF] Brandt | Origin of Antarctic Isopoda (Crustacea, Malacostraca)[END_REF] and even promoting evolutionary radiations of the benthic fauna [START_REF] Wilson | Ocean barriers and glaciation: evidence for explosive radiation of mitochondrial lineages in the Antarctic sea slug Doris kerguelenensis (Mollusca, Nudibranchia)[END_REF][START_REF] Allcock | On the confusion surrounding Pareledone charcoti (Joubin, 1905)(Cephalopoda: Octopodidae): endemic radiation in the Southern Ocean[END_REF][START_REF] Raupach | Molecular data reveal a highly diverse species flock within the munnopsoid deep-sea isopod Betamorpha fusiformis (Barnard, 1920)(Crustacea: Isopoda: Asellota) in the Southern Ocean[END_REF]. These major environmental changes could have also resulted in cryptic speciation in brooding species and broadcasting species with limited larval dispersal capabilities, by the maintenance of genetic differentiation at local scales [START_REF] Thatje | Effects of capability for dispersal on the evolution of diversity in Antarctic benthos[END_REF].

Finally, the Antarctic Circumpolar Current hypothesis predicts the "existence of many species in clades of varied divergence times, at a wide range of depths, but with highest diversity downstream of the Drake Passage, in the Scotia Arc and Weddell Sea" (sic. [START_REF] Pearse | Brooding and species diversity in the Southern Ocean: selection for brooders or speciation within brooding clades? Smithsonian at the poles: contributions to international polar year science[END_REF].

This hypothesis could explain some of the diversification patterns we have observed in asteroids. Nevertheless, the apparent correlation with past geological and climatic events should be taken with great care due to the lack of fossil records and uncertainties in calibration of the molecular clock also known to be taxon and climate regime dependent [START_REF] Gillooly | The rate of DNA evolution: effects of body size and temperature on the molecular clock[END_REF].

CONCLUSION & FUTURE PROSPECTS

The observed genetic patterns of Southern Ocean sea stars highlight the relevance of considering life history traits to understand spatial patterns of genetic diversity. Our results suggest that reproductive strategy could have conditioned the spatial structuring of genetic diversity, but with no apparent effect on the level of genetic diversity. Molecular results also indicate that an in-depth taxonomic revision of the group is needed based on an integrative taxonomy approach (combining genetic and morphological data). The increasing development of genetic surveys in biodiversity conservation and management plans [START_REF] Goodall-Copestake | On the comparison of population-level estimates of haplotype and nucleotide diversity: a case study using the gene cox1 in animals[END_REF] stresses the need for robust estimates of species diversity. Species complexes are frequent in the Southern Ocean (e.g. [START_REF] Hemery | Comprehensive sampling reveals circumpolarity and sympatry in seven mitochondrial lineages of the Southern Ocean crinoid species Promachocrinus kerguelensis (Echinodermata)[END_REF] and estimates of species diversity based on morphology can lead to under-or alternatively, overestimating 'true' biological diversity. In that context, multi-locus approaches are essential to detect evolutionary processes within species. Finally, the apparent bipolar or cosmopolitan distribution of the species B. vexillifer should be further investigated using additional specimens and multiple molecular markers. This will bring new insights on a potential deep-sea route connecting the two polar oceans and the relevance of biogeographic scenarios such as the thermohaline expressway [START_REF] Strugnell | The thermohaline expressway: the Southern Ocean as a centre of origin for deep-sea octopuses[END_REF] and the sub-Antarctic emergence (Diaz et al., 2011). The presence of B. loripes on the continental shelf could be the result of a past colonisation from the deep sea [START_REF] Strugnell | The Southern Ocean: source and sink? Deep Sea Research Part II[END_REF], which potentially challenges the established paradigm of an isolated Southern Ocean benthic diversity [START_REF] Clarke | Evolution and diversity of the benthic fauna of the Southern Ocean continental shelf[END_REF].

ACKNOWLEDGMENTS

The work was supported by a "Fonds pour la formation à la Recherche dans l'Industrie et l'Agriculture" (FRIA) grant to C. Moreau. This is contribution no. 32 to the vERSO project

INTRODUCTION

The "Mesozoic Marine Revolution" (ca. 250-66 Mya; [START_REF] Vermeij | The Mesozoic marine revolution: evidence from snails, predators and grazers[END_REF] has profoundly conditioned the evolution of modern marine benthic fauna and the structure of species interactions within communities. This revolution led to the diversification of durophagous (skeleton-breaking) predators like teleost fish, sharks, rays, predatory molluscs, and decapod crustaceans [START_REF] Thies | Phylogeny and evolutionary ecology of Mesozoic Neoselachii[END_REF][START_REF] Vermeij | The dispersal barrier in the tropical Pacific: implications for molluscan speciation and extinction[END_REF][START_REF] Aronson | Global climate change and the origin of modern benthic communities in Antarctica[END_REF]. It drove shallowwater invertebrates into an ecological arms race to rapidly evolve anti-predatory adaptations (e.g. architectural defences; [START_REF] Meyer | Adaptive radiation of the comatulid crinoids[END_REF][START_REF] Vermeij | The Mesozoic marine revolution: evidence from snails, predators and grazers[END_REF]1987;[START_REF] Roy | Effects of the Mesozoic Marine Revolution on the taxonomic, morphologic, and biogeographic evolution of a group: aporrhaid gastropods during the Mesozoic[END_REF]. In contrast, other invertebrates, like stalked crinoids and brachiopods did not adapt to new conditions and consequently disappeared from the shallows and currently inhabit deep-sea environments in most modern seas [START_REF] Wilson | Some of the deep-sea fauna is ancient[END_REF].

Key stages in the evolution of Southern Ocean marine fauna have shaped its unique biological features and life history traits, such as the high prevalence of brooding and the adaptation to sub-zero temperatures [START_REF] Crame | Key stages in the evolution of the Antarctic marine fauna[END_REF]. Unlike anywhere else in the global ocean, modern Antarctic marine benthic communities comprise of very few durophagous predators, if any [START_REF] Aronson | Climate change and invasibility of the Antarctic benthos[END_REF], conferring the Southern Ocean marine benthos a Palaeozoic-like composition (ca. 540-250 Mya; [START_REF] Bowden | A lost world? Archaic crinoiddominated assemblages on an Antarctic seamount[END_REF]. However, extant Antarctic fauna is believed to be the result of more recent, Cenozoic (last 66 Myr) in situ diversifications [START_REF] Clarke | Evolution and diversity of the benthic fauna of the Southern Ocean continental shelf[END_REF]. Based on the fossil record of the La Meseta Formation in Seymour Island (Antarctic Peninsula), palaeobiological studies indicate that most shallowwater durophagous predators disappeared from Antarctica at the Eocene-Oligocene transition, an age marked by a sudden drop in sea water temperatures (ca. 34 Mya; see for instance [START_REF] Aronson | Global climate change and the origin of modern benthic communities in Antarctica[END_REF]. This transition allowed echinoderm-dominated communities to re-flourish in predatorless environments of the Southern Ocean [START_REF] Stott | The evolution of Antarctic surface waters during the Paleogene: Infer-ences from the stable isotope composition of planktonic foraminifers, ODP Leg 113[END_REF][START_REF] Aronson | Global climate change and the origin of modern benthic communities in Antarctica[END_REF][START_REF] Crame | Key stages in the evolution of the Antarctic marine fauna[END_REF]. There is fossil evidence that asteroid evolution followed this general trend, with local extinction of Southern Ocean taxa at the end of the Eocene, including the highly calcified members of the families Goniasteridae and Oreasteridae [START_REF] Blake | Eocene stelleroids (Echinodermata) at Seymour Island, Antarctic Peninsula[END_REF], which currently occur in modern seas outside the Southern Ocean. Nevertheless, our current knowledge of the deep time evolution of sea stars is limited due to the incompleteness of the fossil record [START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF].

the Census of Antarctic Marine Life (CAML 2005(CAML -2010)), which revealed significant gaps in our knowledge of the Southern Ocean diversity, its origin and evolution (e.g. [START_REF] Clarke | Evolution and diversity of the benthic fauna of the Southern Ocean continental shelf[END_REF][START_REF] Riesgo | Evolutionary patterns in Antarctic marine invertebrates: An update on molecular studies[END_REF]. This holds true for sea stars, for which the variety of pathways and processes that shaped their evolution in the Southern Ocean remains unclear. In this study, we analyse the spatial structure of taxonomic and genetic diversity in Southern Ocean sea stars, through the exploration of an extensive phylogeny reconstruction based on over 4,400 barcode sequences. We use a macro-ecological approach to ascertain the origin, evolution and current diversity of Southern Ocean sea stars, assessing the relevance of a recent diversification scenario and challenging the existence of a latitudinal diversity gradient.

MATERIALS AND METHODS

Richness data compilation

We used a combination of global scale and Southern Ocean-centred studies to explore sea star richness across scales [START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF], Moreau et al., 2018). The Antarctic and sub-Antarctic Asteroidea database assembled by [START_REF] Moreau | Antarctic and sub-Antarctic Asteroidea database[END_REF] was used to describe the geographic distribution of richness patterns with regards to sampling effort along a latitudinal gradient. Quantification of sampling effort, species and genus richness as well as the species:genus ratio, were calculated at a 1° latitude band resolution (from -45° to -79°) based on taxonomic names from the World Register of Marine Species (WoRMS, 2019). A Spearman correlation was performed to test for dependence between sampling effort and taxonomic richness, both at species and genus level. A detailed comparison of the South American and New Zealand quadrants (Longitudes: -20° to -80° and -160° to 135°, respectively) was used to assess longitudinal effects on the diversity gradients. Species accumulation curves following latitude were calculated along both quadrants with PRIMER 6 [START_REF] Clarke | User manual/tutorial[END_REF]. The Jacknife2 extrapolator index was used to correct sampling effort and the UGE index [START_REF] Ugland | The species-accumulation curve and estimation of species richness[END_REF] was used for a comparison with a random distribution (mean value over 999 permutations).

In order to reduce mistakes due to spurious identifications and ambiguous or inaccurate phylogenetic assumptions, the phylogenetic tree was constructed using all sequences at once and some members of the class Ophiuroidea (i.e. Gorgonocephalus arcticus and Ophiura albida) were used as outgroups, as suggested by Linchangco and colleagues (2017). The rarely encountered genus Xyloplax, which has an unclear taxonomic status [START_REF] Janies | Echinoderm phylogeny including Xyloplax, a progenetic asteroid[END_REF] was not included in the present work. Six clades from the entire global data set were selected for detailed phylogeographic analyses: Ganeriidae (n=108), Benthopectinidae

RESULTS

Sea star taxonomic diversity in the Southern Ocean

The seven orders of the class Asteroidea are recorded in all investigated areas of the Southern Ocean (Table 6). Out of the 38 existing families, 26 (68%) are present in the Southern Ocean and 24 (63%) south of the Polar Front. A total of 344 genera and 1,892 species of asteroids have been described worldwide [START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF]. Out of these, 116 (34%) and 79 (23%) genera are reported in the Southern Ocean and the Antarctic Zone (i.e. south of the Polar Front), respectively. At species level these values range from 294 (16%) in the entire Southern Ocean to 196 (10%) south of the Polar Front. Endemism estimates are lower at higher taxonomic levels with no order nor family being restricted to the Southern Ocean, while 27 genera (23%) and 176 species (60%) exclusively inhabit Southern Ocean waters. South of the Polar Front, endemism decreases to 1 genus (1%) and 56 species (29%). The single endemic genus, Caimanaster, being monotypic and recorded by one immature specimen only (Table 6). **Doubtful occurrences were removed in line with a conservative approach. Luidia clathrata and Asthenactis australis were excluded as the first one is only known from warm shallow waters and the second from a single specimen at the edge of the Southern Ocean.

Latitudinal trends in the Southern Ocean

Overall, genus and species richness decrease as latitude increases south of 45°S (Figure 31B) following a pattern that strongly matches sampling effort. The correlation between sampling effort and species and genus richness is highly significant (Spearman's r, p<0.005) with rs values of 0.82 and 0.75 respectively. Richness decreases sharply in three latitude ranges: -55° to -60°; -68° to -70° and -78° to -79° (Figure 31A andB). These latitudes correspond to undersampled deep-sea basins and the restricted amount of seabed at the higher latitudes in the Southern Ocean. The species:genus ratio remains relatively constant with latitude, with a mean value of 1.58 ± 0.23 (Figure 31B). Under-sampled latitudes, however, also show a marked decrease in the species:genus ratio.

Latitudinal patterns differ between West (South American quadrant) and East (New Zealand quadrant). In the East, species and genus richness follow a bimodal distribution corresponding to the East Antarctic and the New Zealand plateau separated by a deep-sea basin (Figure 31C). In the West, the highest values are recorded in the Antarctic Peninsula (Figure 31D).

Species accumulation curves following latitude show distinct gradients between West and East (Figure 31C andD). In the West, observed values (SObs) approximately follow the random pattern of species accumulation (UGE index), indicating a constant turnover of species with latitude. The curve of extrapolated richness values (Jacknife2 index) predicts potentially greater richness values in the Antarctic Peninsula and South America due to the scarcity of sampling effort in these areas compared to the Scotia Arc and the Weddell Sea (Figure 31D).

In the East, observed values (SObs) remain relatively low compared to the random curve (UGE index) showing a marked increase at the latitudes of the New Zealand plateau (Figure 31C)

and the presence of a distinct New Zealand fauna. Overall, extrapolated richness values using the Jacknife2 index indicate incomplete sampling effort and a potentially higher richness in both quadrants (Figure 31C and D) as well as in the entire Southern Ocean (Appendix 3).

Global phylogenetic exploration

Genetic data is available for all seven asteroid orders. Out of 38 families described within the class Asteroidea, 28 are represented by at least one sequence and 25 of them have representatives dwelling in deep or cold environments ( The phylogenetic tree reconstruction included 4,440 sequences (length of at least 600 bp) representing 2,201 unique haplotypes (Figure 32). Alignment is not problematic, and no stop codons are found. Apart from the order Brisingida, no ordinal nor superordinal levels of the accepted sea star taxonomy are retrieved in the reconstructed tree (Figure 32). Ten of the accepted sea star families represented by more than one genus are recovered as monophyletic with good support (e.g. Ganeriidae, Solasteridae, Benthopectinidae), while others are paraphyletic (e.g. Asterinidae, Oreasteridae, Poraniidae, Astropectinidae) (see Figure 32 for the complete list). Based on the accepted nomenclature of families and delimitation of the Forcipulatacean by Mah and Foltz (2011a), 55 clades are retrieved (Figure 32). Among them, 27 contained sequences from specimens collected in the Southern Ocean.

Nineteen of the clades with Southern Ocean representatives also encompassed specimens from outside the Southern Ocean, while eight clades are composed uniquely of Southern Ocean specimens (see Figure 32).

Phylogeographic patterns

The main phylogeographic patterns observed in this study are illustrated in Figure 33 and detailed below with examples drawn from the six clades of interest and from previous studies with complementing patterns (i.e. Glabraster, [START_REF] Moore | The Antarctic Circumpolar Current isolates and connects: Structured circumpolarity in the sea star Glabraster antarctica[END_REF]Bathybiaster, Moreau et al., 2019).

Our results indicate several cases of either cryptic species or unidentified taxa (e.g.

genus Perknaster, Acodontaster, Henricia; see Appendix 3). A case in point is the genus Rhopiella (endemic to the Southern Ocean) that displays a particularly high level of species richness (Appendix 3). To date, only one species of Rhopiella has been described, while 15 clades are delineated here with substantial genetic divergence between them (Figure 33;

Table 8). The spatial structure found in some of these analyses also indicates depth or geomorphology-related differences, as in the genus Bathybiaster (Figure 33) within which B.

loripes is only found around the Antarctic shelves while B. vexillifer, its sister species only occurs in the deep sea, except for the Kerguelen Plateau (Figure 33). Overall, the phylogenetic analysis highlights many discrepancies between molecular results and current taxonomy based on morphological identifications. Our results show that all six investigated families require systematic revision based on species delineation and morphological identification (see Table 8; Appendix 3). For example, in the species Odontaster meridionalis, sequences at our disposal, together with the global phylogenetic tree, suggest that specimens belong to another family. Such identification mismatches are however common in DNA barcoding: specimens could have been either misidentified or samples have been contaminated in former studies (e.g. [START_REF] Janosik | Evolutionary history of Southern Ocean Odontaster sea star species (Odontasteridae; Asteroidea)[END_REF]Clades V and VI). Deeper phylogenetic relationships also departed from the accepted taxonomy with the polyphyly of the genera Solaster, Crossaster, Lophaster, Paralophaster and Pteraster.

DISCUSSION

Spatial and taxonomical diversity in the Southern Ocean

Uneven sampling effort is one of the main methodological limitations hampering large scale macro-ecological studies in the Southern Ocean and can generate misleading diversity patterns. In our work, spatial patterns of sea star species and genus richness are clearly correlated with sampling effort, as previously demonstrated for molluscs [START_REF] Clarke | How well do we know the Antarctic marine fauna? A preliminary study of macroecological and biogeographical patterns in Southern Ocean gastropod and bivalve molluscs[END_REF].

Furthermore, we found no conclusive evidence of a declining latitudinal gradient in species nor genus richness in the entire Southern Ocean, in contrast with other marine groups like gastropods, bivalves, pycnogonids, and echinoids [START_REF] Clarke | How well do we know the Antarctic marine fauna? A preliminary study of macroecological and biogeographical patterns in Southern Ocean gastropod and bivalve molluscs[END_REF]David & Saucède, 2015).

The lower number of genera observed south of the Polar Front may reflect reduced sampling effort in this zone, but also the effect on our analysis of the rich and distinct fauna present off southern New Zealand [START_REF] Moreau | Reproductive strategy as a piece of the biogeographic puzzle: a case study using Antarctic sea stars (Echinodermata, Asteroidea)[END_REF].

Although the influence of sampling bias cannot be denied, some contrast in diversity is observed between the South American and New Zealand quadrants. This can be explained by distinct geomorphological features, the South American quadrant offering a continuum of emerged ridges (Scotia Arc), while a deep basin separates New Zealand from Antarctica. The bell-shaped richness pattern obtained from South America to Antarctica could reflect the role of the Antarctic Peninsula and Scotia Arc region as a diversification centre [START_REF] Linse | Macro-and megabenthic assemblages in the bathyal and abyssal Weddell Sea (Southern Ocean)[END_REF], promoting speciation by vicariance around the numerous islands of the area. Furthermore, the constant turnover in species composition observed with latitude in the South American quadrant might reflect a mixing of Antarctic and Magellanic faunas favoured by a 'stepping stone' effect along the Arc [START_REF] Moreau | Reproductive strategy as a piece of the biogeographic puzzle: a case study using Antarctic sea stars (Echinodermata, Asteroidea)[END_REF]. In contrast, high richness values are observed north and south of the deep-sea basin separating Antarctica from New Zealand with evidence of distinct faunas. This indicates little faunal exchange between the two distant regions.

The relatively constant species:genus ratio measured with latitude suggests a lack of specialisation and/or higher diversification of genera at high latitudes [START_REF] Krug | Signature of the end-Cretaceous mass extinction in the modern biota[END_REF]. This is not in line with species diversification and adaptation patterns reported for other marine groups (see, e.g. for notothenioid fish, [START_REF] Eastman | Fishes on the Antarctic continental shelf: evolution of a marine species flock?[END_REF]for echinoids, Saucède et al., 2014). Similarly, the wide taxonomic range of Southern Ocean asteroids, here confirmed by both morphological and molecular approaches, supports the hypothesis of continuous and recent faunal exchange between the Southern Ocean and other adjacent regions. Most of the Southern Ocean families include members widely distributed in cold-water or deep-sea environments elsewhere [START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF]. As already proposed for holothurians [START_REF] O'loughlin | The Antarctic region as a marine biodiversity hotspot for echinoderms: diversity and diversification of sea cucumbers[END_REF], this could indicate that suitable biotic and abiotic conditions have facilitated species exchange between the Southern Ocean and northernmost regions and their local settlement. This could account for the wide diversity and ecological success of asteroids in the Southern Ocean. Such a scenario may also explain the apparent absence of species flocks in Southern Ocean asteroids unlike many other classes of vertebrates and invertebrates (see [START_REF] Lecointre | Is the species flock concept operational? The Antarctic shelf case[END_REF]. Altogether, diversity patterns support the hypothesis of the recent colonisation of the Southern Ocean by asteroids that originated in northernmost regions in environments with similar abiotic conditions such as the deep sea [START_REF] Brandt | On the origin and evolution of Antarctic Peracarida (Crustacea, Malacostraca)[END_REF].

Morphological and genetic evidence shows that the diversity of Southern Ocean asteroids has been largely overlooked and most families are still in crucial need of taxonomic revision as already emphasised in previous research (e.g. [START_REF] Janosik | Evolutionary history of Southern Ocean Odontaster sea star species (Odontasteridae; Asteroidea)[END_REF][START_REF] Moreau | Is reproductive strategy a key factor in understanding the evolutionary history of Southern Ocean Asteroidea (Echinodermata)?[END_REF]. This is particularly topical and feasible given the recent development of molecular studies (e.g. [START_REF] Layton | Exploring Canadian echinoderm diversity through DNA barcodes[END_REF][START_REF] Christiansen | Diversity of Mesopelagic Fishes in the Southern Ocean. A Phylogeographic Perspective Using DNA Barcoding[END_REF]. Several explanations can account for such a discrepancy between current taxonomy and molecular results. Mainly, 1) the lack of clear identifying tools and resources (e.g. up-to-date, interactive taxonomic keys); 2) the presence of highly polymorphic species (e.g. Glabraster antarctica) or, on the contrary, of morphologically very similar species complexes (e.g. Rhopiella hirsuta); 3) the subjectivity of identifiers (interpretation of characters, geographic location); and 4) the preservation method/status of specimens that affects morphological identification. Ways to improve the situation include the increased use of integrated taxonomy, including large-scale, standardised DNA barcoding using COI and additional genetic markers, the creation of robust diversity baselines and updated identification keys.

Large scale phylogenetic patterns

Phylogenetic results suggest that a recent and rapid diversification occurred in most clades of Southern Ocean sea stars, a situation common to other benthic taxa in the Southern

Ocean (e.g. ophiuroids, [START_REF] Sands | Against the flow: evidence of multiple recent invasions of warmer continental shelf waters by a Southern Ocean brittle star[END_REF]molluscs, González-Wevar et al., 2017;amphipods, Verheye et al., 2017). These results corroborate recent phylogenomic findings on ophiuroids from the Southern Hemisphere [START_REF] O'hara | Contrasting processes drive ophiuroid phylodiversity across shallow and deep seafloors[END_REF], which challenged the idea that diversification rates are low in polar regions, confirming similar observations found in fishes [START_REF] Rabosky | An inverse latitudinal gradient in speciation rate for marine fishes[END_REF]. Although contemporary asteroid diversity is likely the highest in tropical regions [START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF], the dogma that thermal energy promotes diversification is clearly contested by our results. Rapid diversification could also explain the existence of many species complexes that are problematic to taxonomists who rely solely on morphological assessments. The influence of in situ environmental disturbance on diversification processes, via the impact of glacial-interglacial cycles, sometimes referred to as the 'Antarctic diversity pump' hypothesis [START_REF] Clarke | The origin of the Southern Ocean marine fauna[END_REF][START_REF] Brandt | Origin of Antarctic Isopoda (Crustacea, Malacostraca)[END_REF], may be the main driver of the observed diversity patterns. Other hypotheses could also explain these rapid diversifications, and notably a temporal succession between successful settlement events and divergence processes by vicariance (ACC hypothesis in [START_REF] Pearse | Brooding and species diversity in the Southern Ocean: selection for brooders or speciation within brooding clades? Smithsonian at the poles: contributions to international polar year science[END_REF].

The suggested faunal affinities between the Southern Ocean and the adjacent regions support the scenarios of recent and recurrent faunal exchanges with South America and New

Zealand (Mah & Foltz, 2011b;[START_REF] Moreau | Reproductive strategy as a piece of the biogeographic puzzle: a case study using Antarctic sea stars (Echinodermata, Asteroidea)[END_REF] Glabraster antarctica; Odontaster roseus), New Zealand (e.g. Psilaster charcoti; 'Cheiraster complex') or both (Hippasteria phrygiana; [START_REF] Foltz | Global population divergence of the sea star Hippasteria phrygiana corresponds to the onset of the last glacial period of the Pleistocene[END_REF].

For species endemic to, or mainly distributed in the Southern Ocean, phylogeographic patterns obtained in this study are congruent with previous biogeographic works on sea stars [START_REF] Moreau | Reproductive strategy as a piece of the biogeographic puzzle: a case study using Antarctic sea stars (Echinodermata, Asteroidea)[END_REF]. These patterns include the presence of: 1) affinities of sub-Antarctic species, especially between South America and the Kerguelen Plateau (e.g. Odontaster penicillatus; Cycethra verrucosa) and often including South Georgia or other Antarctic islands like the Balleny Islands (e.g. Acodontaster sp1); 2) circumpolarity of species present on the continental shelf (Odontaster validus; Acodontaster sp2; Cuenotaster involutus; Bathybiaster loripes) or the entire Southern Ocean (Glabraster antarctica; [START_REF] Moore | The Antarctic Circumpolar Current isolates and connects: Structured circumpolarity in the sea star Glabraster antarctica[END_REF] and 3) a partition between East and West Antarctic species (Notasterias spp; Lysasterias spp; Diplasterias spp) [START_REF] Moreau | Is reproductive strategy a key factor in understanding the evolutionary history of Southern Ocean Asteroidea (Echinodermata)?[END_REF].

Global barcode library -an asset for future studies.

Using mtDNA barcoding only provides a limited amount of information (see [START_REF] Halanych | Challenging Dogma Concerning Biogeographic Patterns of Antarctica and the Southern Ocean[END_REF], but this approach has proved useful to gain background knowledge of taxonomy, population genetics and molecular phylogenetics [START_REF] Hajibabaei | DNA barcoding: how it complements taxonomy, molecular phylogenetics and population genetics[END_REF]. Deeptime relationships among distant taxonomic groups (i.e. between orders) cannot be inferred using COI mtDNA. However, even though the present work did not aim at resolving the global phylogeny of asteroids, using all sequences at once revealed similar topologies as in multigenes phylogenies (see Mah & Foltz, 2011a, b), at least at the family level. Wrongly associated groupings can result from the lack of representative sampling, taxonomic issues, molecular saturation of COI barcode fragments or misidentifications.

Efficient barcode libraries also help pinpoint: 1) dubious identifications, and 2) target clades for further analysis. There is, however, a crucial need to increase the number of sampled taxa to improve the resolution and correctness of phylogenies and our understanding of Antarctic benthic diversity [START_REF] Hajibabaei | DNA barcoding: how it complements taxonomy, molecular phylogenetics and population genetics[END_REF]. In a period of growing interest in identifying and managing marine protected areas, accurate and exhaustive barcode libraries can represent a valuable asset for biodiversity assessments and should receive more consideration. For example, [START_REF] Schander | What can biological barcoding do for marine biology?[END_REF] showed that reports on North Atlantic marine phyla could only identify two thirds of species with precision. By providing a reference for specimen identification, including juveniles and larvae [START_REF] Webb | DNA barcoding: a molecular tool to identify Antarctic marine larvae[END_REF], especially for poorly studied taxa, these databases could reduce misleading interpretations of results in several domains of expertise (e.g physiology; modelling).

CONCLUSION

In the present study, we demonstrate that barcode libraries can be useful to analysing and understanding large-scale marine systems. Our results indicate that significant diversification events occurred recently in many clades of Southern Ocean sea stars and also highlight the important discrepancy between current taxonomy and molecular data. In addition to describing phylogeographic patterns, scenarios were proposed to explain the origin and evolution of Southern Ocean sea stars. The main scenario suggests that successive invasion and exchange events occurred between the Southern Ocean and adjacent regions with comparable environmental conditions, during periods of rapid climate change. To test for the relevance of these proposed scenarios, a significant effort should be made in terms of:

1) sampling effort, especially in deep-sea environments, East Antarctica but also in surrounding areas like South Africa or the south Atlantic islands; 2) valorisation of existing museum collections; 3) use of multi-locus molecular markers; and 4) collaboration between marine biologists working on sea stars worldwide, cooperation between biologists and the repetition of analyses also contributing to improve the accuracy of biodiversity assessments.

ACKNOWLEDGMENTS

The work was supported by a "Fonds pour la formation à la Recherche dans l'Industrie et

General discussion

Since its discovery and first explorations of its ecosystems, the Southern Ocean never stopped fascinating explorers and scientists. Despite the ever-growing interest into studying these high latitudes, difficulties to access the southernmost ocean and continent have shaped the relatively poor scientific knowledge of these atypical environments, as underlined by the first Horizon Scan conducted by the Scientific Committee for Antarctic Research (SCAR; [START_REF] Kennicutt | Polar research: six priorities for Antarctic science[END_REF][START_REF] Kennicutt | A roadmap for Antarctic and Southern Ocean science for the next two decades and beyond[END_REF]. Recent efforts, notably the Census of Antarctic Marine Life (CAML; [START_REF] Schiaparelli | The Census of Antarctic Marine Life: the first available baseline for Antarctic marine biodiversity[END_REF], are adding knowledge to a legacy of 150 years of scientific investigations, allowing major improvements in our understanding of the Southern Ocean. As a consequence, incompleteness in the spatial and temporal cover of biological (see [START_REF] Griffiths | Data distribution: Patterns and implications. Biogeographic atlas of the Southern Ocean[END_REF][START_REF] Gutt | Correlative and dynamic species distribution modelling for ecological predictions in the Antarctic: a cross-disciplinary concept[END_REF] and environmental [START_REF] Post | Environmental Setting. Biogeographic Atlas of the Southern Ocean[END_REF][START_REF] Trull | Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment[END_REF] records has inevitably decreased over time, but the effect of this biases on macroecological studies persists (e.g. [START_REF] Pierrat | Comparative biogeography of echinoids, bivalves and gastropods from the Southern Ocean[END_REF]Fabri-Ruiz et al., 2018). During my thesis, a significant effort has been made to compile the results of decades of scientific collaborations under the form of an extensive asteroid occurrence database (Figure 34; [START_REF] Moreau | Antarctic and sub-Antarctic Asteroidea database[END_REF] together with a barcode library, initiated in the CAML framework [START_REF] Schiaparelli | The Census of Antarctic Marine Life: the first available baseline for Antarctic marine biodiversity[END_REF]. Despite the improved availability of data, this thesis highlights the importance of sampling bias and the need for more and a better use of data (Chapters 1, 2 and 3).

This manuscript also happens at a time when the classic viewpoint about diversity and biogeographic patterns of marine life in the Southern Ocean are more and more often challenged and refined by technological development in term of scientific or operational methods (e.g. Koubbi et al., 2014). Some ideas such as the high levels of endemism seem well founded but other postulations like the circumpolar distribution of most Antarctic species, their Gondwanan origin or the low diversity level of polar communities may well be based on simplistic or incorrect assumptions [START_REF] Halanych | Challenging Dogma Concerning Biogeographic Patterns of Antarctica and the Southern Ocean[END_REF]. Refining our understanding of diversity distribution in the Southern Ocean will bring a better knowledge of the drivers at play in the determination of biogeographic patterns.

a. Sea star diversity in the Southern Ocean

An ill-evaluated diversity Morphology-based Taxonomy, by attributing species names to organisms, is the founding work and usually first approach used for biodiversity studies. As species are often the basal units of ecological studies, accurate identification is essential to carry on robust scientific investigations. One of the main results highlighted by molecular works from Chapters 2 and 3 is however the obsolete nature of species taxonomy of many Southern

Ocean sea star representatives. In nearly all the investigated families, discrepancies were found between morphology-based identifications and results obtained using molecular tools.

Since the earliest descriptions (e.g. [START_REF] Bell | Contributions to the Systematic Arrangement of the Asteroidea. The Species of the genus Asterias[END_REF][START_REF] Sladen | Report on the scientific results of the voyage of HMS Challenger during the years 1873-76[END_REF], the taxonomy of sea star genera has been subject to many changes, reappraisals and keeps being reassessed either based on diagnostic morphological characters or using molecular tools [START_REF] Janosik | Unrecognized Antarctic biodiversity: a case study of the genus Odontaster (Odontasteridae; Asteroidea)[END_REF][START_REF] Mah | New taxa and taxonomic revisions to the Poraniidae (Valvatacea; Asteroidea) with comments on feeding biology[END_REF][START_REF] Mah | New taxa and taxonomic revisions to the Poraniidae (Valvatacea; Asteroidea) with comments on feeding biology[END_REF]. The studied genera (Chapter 2) make no exception. Tedious was the task to differentiate species based on morphological characters but even more tedious is the task to extract a clear diagnosis from the many descriptions, re- descriptions and synonymies established for each species (e.g. [START_REF] Koehler | Echinodermes (Astéries, Ophiures et Echinides) recueillis par M. Rallier du Baty, aux Iles de Kerguelen, en 1913-1914[END_REF][START_REF] Koehler | Echinodermata: Asteroidea. Scientific Reports[END_REF][START_REF] Bell | Contributions to the Systematic Arrangement of the Asteroidea. The Species of the genus Asterias[END_REF][START_REF] Clark | BANZ Antarctic Research Expedition[END_REF]. The systematics of the broadcasting genera Bathybiaster and Psilaster have, for example, been subject to discussion for almost a century when in 1923, HL Clark pointed out the morphological similarities between B. vexillifer and B. loripes in his work on the echinoderm fauna of South Africa [START_REF] Clark | The echinoderm fauna of South Africa. Trustees of the South African Museums[END_REF]. Later, [START_REF] Fisher | Asteroidea[END_REF] Bathybiaster and Psilaster should be assigned to distinct genera [START_REF] Mortensen | Handbook of the Echinoderms of the British Isles[END_REF]. More recently, [START_REF] Clark | Starfishes of the Atlantic[END_REF] highlighted the important morphological variations within the genus Psilaster (P. charcoti excluded) "making clear identification rather complicated" [START_REF] Clark | Starfishes of the Atlantic[END_REF]. Similarly, the taxonomy of the brooding genera under study has proved to be extremely variable. The first point is a rich synonymy between nominal species of the three genera of interest evidencing important taxonomic issues. In the genus Notasterias, the existence of strong morphological variations in diagnostic characters were pointed out by [START_REF] Clark | BANZ Antarctic Research Expedition[END_REF] who also raised doubts about the distinction between Notasterias stolophora and Notasterias armata. Likewise, he proposed that Notasterias bongraini could be a synonym to Notasterias pedicellaris and indistinguishable from N. armata in dorsal view while diagnostic characters are "not invariable" in ventral view. Similarly, [START_REF] Jangoux | Catalogue commenté des types d'Echinodermes actuels conservés dans les collections nationales belges[END_REF] indicated that Notasterias candicans could be closely related to N. armata. The genus Diplasterias has also been subject to vivid debates. [START_REF] Koehler | Echinodermes (Astéries, Ophiures et Echinides) recueillis par M. Rallier du Baty, aux Iles de Kerguelen, en 1913-1914[END_REF] questioned the assignment of Diplasterias spinosa to the genus Diplasterias but described it from a single specimen in bad conservation state. This same year, he described the new species Diplasterias kerguelensis based on juveniles, although individuals at this stage can lack species diagnostic characters and therefore belong to an already described species. In 1962, Clark expressed his doubts about the taxonomic difference between D. brucei and D. brandti and later, [START_REF] Fisher | Asteroidea[END_REF] indicated that a six-rayed Diplasterias octoradiata could "give future systematicists something to puzzle over" regarding its resemblance with D. meridionalis. Finally, the genus Lysasterias makes no exception to the above remarks. [START_REF] Fisher | Asteroidea of the North Pacific and adjacent waters. Part 3. Forcipulata[END_REF] questioned the validity of the genus diagnostic characters. Later, in 1940, he showed evidence of skeleton degeneration with age certainly leading to character misinterpretation. He also highlighted the polymorphism of Lysasterias perrieri, the putative synonymy between Lysasterias hemiora and L. perrieri, the similarity between Lysasterias heteractis and a L. perrieri with eight arms and stressed the critical effect of preservation on species identification.

Similar conclusions might undoubtedly be drawn for other representatives of the Asteroidea when more thorough investigations will be undertaken (see Chapter 3). Several factors can be listed to account for taxonomic issues. 1) The lack of clear identifying tools and resources (e.g. interactive taxonomic keys), the identification of species based on their known biogeographic distribution only (Diaz et al., 2011;[START_REF] Saucède | The phylogenetic position and taxonomic status of Sterechinus bernasconiae Larrain, 1975 (Echinodermata, Echinoidea), an enigmatic Chilean sea urchin[END_REF], on juveniles [START_REF] Roberts | Southern Ocean Pteropods. Biogeographic Atlas of the Southern Ocean[END_REF] or on inappropriately preserved specimens [START_REF] Meyer | Limitations in global information on species occurrences[END_REF].

2) The focalisation of specialists on restricted geographic areas without considering the surrounding regions and neglecting per consequence the work of other taxonomists.

3) The presence of cryptic species, species complexes or highly polymorphic species making the assessment of diversity based on morphology only rather troublesome.

To overcome the baffling problem of accurate morphology-based identification, several solutions exist but require an important investment in time and money. First, there is a need for a compiling effort of the existing literature describing species synonymy, diagnosis and morphology. Secondly, the creation of a baseline based on barcode DNA sequences would ensure relevant specimens' identification as it has been demonstrated to be a valuable approach for other organisms [START_REF] Hebert | Biological identifications through DNA barcodes[END_REF] (Grant et al., 2010) to create a baseline using DNA barcoding. Although this work was substantial and represented a great advance in the building of an extensive and efficient barcode library, many efforts are still needed. Other assets of extensive barcode libraries include the characterisation of juveniles or larvae for which only little is known in most species while they have an important role in determining distribution patterns [START_REF] Heimeier | Using DNA barcoding and phylogenetics to identify Antarctic invertebrate larvae: Lessons from a large scale study[END_REF][START_REF] Janosik | Short Note: Life history of the Antarctic sea star Labidiaster annulatus (Asteroidea: Labidiasteridae) revealed by DNA barcoding[END_REF]; Chapter 1 and 2).

Sampling bias is another considerable constraint to meaningful assessments of Southern Ocean sea star diversity. Despite significant technological advances since the age of the first pioneers, fieldwork remains very costly, time consuming and challenging today. A more thorough sampling effort is still necessary at the scale of the entire Southern Ocean [START_REF] Griffiths | Data distribution: Patterns and implications. Biogeographic atlas of the Southern Ocean[END_REF]. The high correlation between sampling effort and species richness as showed in Chapter 3; species accumulation curves of Chapter 1, which rarely reach the asymptote; and the Jacknife extrapolator index predicting the presence of ~370 species (+32%) in Chapter 1 and 3 all suggest that our knowledge of Southern Ocean species richness only represents the tip of the iceberg. Unfortunately, and for obvious logistic reasons, areas located far away from scientific research stations and the common routes of research vessels are seldom investigated [START_REF] Griffiths | Quantifying Antarctic marine biodiversity: The SCAR-MarBIN data portal[END_REF]. Access to biodiversity data on such poorly sampled areas would certainly enhance the quality of analyses and the impact of scientific results. In large-scale studies, this would significantly contribute to filling significant gaps in our understanding of species biogeography. In the absolute, it seems that the quantity and quality of data are lacking for robust and comprehensive studies in the Southern Ocean [START_REF] Griffiths | Data distribution: Patterns and implications. Biogeographic atlas of the Southern Ocean[END_REF]. However, by taking a closer look at the worldwide distribution of sea star records from the Ocean Biogeographic Information System (OBIS), this assertion is somewhat softened. The surrounding waters of three regions of the world have been clearly more investigated than the rest (i.e. North America, western Europe and Indo-Pacific region;

Figure 35), but the Southern Ocean has been subject to broad-scale sampling, even if some areas/regions remain poorly sampled. Using whole oceanwide studies could suggest connectivity patterns despite the absence of samples in these regions. Finally, as presented in Chapters 2 and 3, the Southern Ocean is not a closed and entirely isolated system and many faunal affinities were highlighted with areas located further north. Unfortunately, very few specimens are available from South America or the southern part of Africa while they could help better delineate broad biogeographic patterns and processes. Similarly, the deep-sea remains poorly studied and findings from this thesis argue for oceanwide relationships (ubiquity or bipolarity) and a key role of deep-sea fauna in the origin and evolution of Antarctic biogeographic patterns (Chapter 2 and 3). Easy access to existing samples and data is the last major methodological issue to overcome. Even if marine biologists studying the Southern Ocean collaborate through an international networking and despite the Antarctic Treaty article III.1.c stating, "Scientific observations and results from Antarctica shall be exchanged and made freely available"

(Antarctic Treaty Consultative Parties, 1959), many scientists still remain timorous with the idea of sharing samples and/or data they worked hard to obtain. Furthermore, there is perhaps a profound misunderstanding in the way science is funded in general, with a shift to support more and more applied over fundamental research [START_REF] Courchamp | Fundamental ecology is fundamental[END_REF]. Finally, a gap persists between the (high) funds allocated to new fieldwork expeditions (to obtain more samples, to be physically present for political reasons or to communicate about it) and the (low) allocation to process the enormous amount of samples and data generated by these expeditions. At an individual level, scientists should be encouraged to publish or make accessible their existing samples databases which are often more detailed and linked to various content (photograph, DNA sequence etc…), providing more exhaustive information than expedition reports or occurrences databases.

Following this thought, promoting the use of museum collections would greatly contribute to improving the taxonomy of many taxa. These collections are underused while they should have a fundamental role in biodiversity assessments. [START_REF] Meineke | Biological collections for understanding biodiversity in the Anthropocene[END_REF] suggest that specimens deposited in natural history museums have the potential to transform the field of global change biology. They also point out the threats due to budget cuts and other institutional pressures that these resources are subject to.

The obvious solution to that final problem is the promotion and funding of exchanges between experts and institutions to study collections but also the training and recruiting of personnel to process existing samples and policies to finance institutions and allocate more funding to process the samples. Some initiatives, like the European Collections Infrastructure SYNTHESYS, which aims at bringing together 115 museums from 21 countries and promotes access and resources for research users in the natural sciences already exist, but such projects need to be developed and extended.

Consequences for the quality of research

As taxon identification is a prerequisite to many biological studies, spurious identifications are not without consequences for biodiversity studies and inventories, generating taxonomic disagreements within the scientific community. This impacts the quality of diversity assessments and scientific outputs in all ecological studies based on taxonomy with sometimes noxious effects on exploitation [START_REF] Garcia-Vazquez | Species misidentification in mixed hake fisheries may lead to overexploitation and population bottlenecks[END_REF], conservation or policy management [START_REF] Mcgeoch | Uncertainty in invasive alien species listing[END_REF]. Ensuring that taxonomy is maintained up to date is particularly important for conservation issues and a wide range of research field, from biogeography to macroecology, species distribution modelling and ecophysiology. Extensive databases like the one used in the present thesis have their own limitations in particular when working at species level. This implies that results presented in Chapter 1 of the present thesis may need to be supported by improved taxonomy at least at species level, although the genetic study presented in Chapter 3 tends to partly support them (see section "patterns").

Similarly, general phylogenies of the class Asteroidea are still not fully reliable. Either based on very few specimens (one per order in [START_REF] Linchangco | The phylogeny of extant starfish (Asteroidea: Echinodermata) including Xyloplax, based on comparative transcriptomics[END_REF] or few genetic markers (three markers and a total length of 1,307 bp in Mah et al., 2010 a and b) these can only reflect little phylogenetic information and might sometimes be misleading. A comparable limitation can be found in the calibration of molecular clocks and the estimation of evolutionary events timings in the Southern Ocean. They are often based on more or less close relatives and mutation rates estimated from other regions (mainly based on mitochondrial markers and the closure of the Isthmus of Panama). Calibration using fossils is an alternative but was not possible in this thesis due to intrinsic issues in sea star fossilisation (incompleteness of the fossil record) and their near absence at high latitudes.

In this framework, the use of advanced molecular tools represents an ideal step forward to address biogeographic issues in the Southern Ocean with accuracy. Results from Chapters 2 and 3 are here to demonstrate that even the use of a single mitochondrial marker (COI) can answer many questions about the evolution, distribution or diversity of benthic organisms as previously highlighted in other studies (e.g. [START_REF] Hemery | Comprehensive sampling reveals circumpolarity and sympatry in seven mitochondrial lineages of the Southern Ocean crinoid species Promachocrinus kerguelensis (Echinodermata)[END_REF][START_REF] González-Wevar | Following the Antarctic Circumpolar Current: patterns and processes in the biogeography of the limpet Nacella (Mollusca: Patellogastropoda) across the Southern Ocean[END_REF]. COI also helps as a basal tool to pinpoint where further investigations are needed like in my work regarding diversity reassessments or faunal affinities. Nevertheless, whether in terms of patterns (endemism, eurybathy, circumpolarity, connectivity) or processes (role of reproductive strategy, timing of radiations, evolutionary history), high-throughput sequencing methods will improve our understanding of Southern Ocean biogeography [START_REF] Halanych | Challenging Dogma Concerning Biogeographic Patterns of Antarctica and the Southern Ocean[END_REF].

Such approaches and methods are still slowly applied to Southern Ocean case studies by the community of Antarctic marine biologists. Only two studies using population genomics on invertebrates is available for the Southern Ocean brittle stars Ophionotus victoriae and Astrotoma agassizii (Galaska et al., 2017a(Galaska et al., , 2017b) ) while this approach holds tremendous potential for understanding the genetic relationships and phylogeography [START_REF] Reitzel | Going where traditional markers have not gone before: utility of and promise for RAD sequencing in marine invertebrate phylogeography and population genomics[END_REF]. Applying these molecular methods can be time-consuming, often taxon-specific and the cost of such analyses is particularly high. Altogether, it represents the main limitations to future developments. It is important to note that applying modern methods does not preclude the importance of more traditional morphology-based methods. Both methods will have to be used in concert in the future to enhance diversity assessments.

b. Distribution and genetic patterns in Southern Ocean sea stars

Biogeography versus phylogeography

By characterising the phylogenetic deployment of lineages in the geography, phylogeography represents new developments in biogeographic studies [START_REF] Arbogast | Comparative phylogeography as an integrative approach to historical biogeography[END_REF]. In the marine realm, biogeography and phylogeography encompass half a billion years of genetic evolution and the largest habitat on the planet making generalisations arduous, but some are especially robust [START_REF] Bowen | Comparative phylogeography of the ocean planet[END_REF]. As postulated at the beginning of this discussion, the Southern Ocean makes no exception when it comes to consider the discrepancies between morphological-based and molecular-based evaluation of diversity, leading to underestimates in the roles of various evolutionary processes (Chapters 2 and 3; [START_REF] Arbogast | Comparative phylogeography as an integrative approach to historical biogeography[END_REF].

Generally speaking, main biogeographic patterns revealed in Chapter 1 for sea stars in the Southern Ocean are congruent with previous studies performed on other taxa (echinoids, bivalves, gastropods, [START_REF] Pierrat | Comparative biogeography of echinoids, bivalves and gastropods from the Southern Ocean[END_REF]amphipods, De Broyer & Jażdżewska, 2014), but these results should be considered carefully. The inconsistencies between morphological and molecular-based identifications highlighted in Chapters 2 and 3 make the interpretations of biogeographical patterns at the species level not as reliable as previously thought. For example, the mixing between South American and Antarctic sea star faunas along the Scotia Arc is not so obvious. South American species seem to have more affinities with those of South Georgia and the sub-Antarctic islands regardless of the reproductive strategy (Chapter 2 and 3). On the contrary, the East-West Antarctic differentiation observed in Chapter 1 is also highlighted by molecular analysis performed on the brooding genera of Chapter 2. Similarly, affinities with New Zealand are confirmed but they seem to be present between species found at deeper depths. Overall, results brought by the global biogeographic analysis are congruent with the phylogeographic analysis. However, the former is based on an extensive database while the latter is more specific and focuses on fewer taxa. In summary, the global investigation of patterns differs from the detailed ones by smoothing the results and building generalities, making a proper comparison of the two approaches rather delicate.

Diversity patterns

The world ocean covers 71% of Earth's surface and provide 900 times more liveable habitat volume than what is available on land (Costello & Chaudhary, 2017). It appears ideal for studying global scale patterns of life distribution with large, well-connected areas at all latitudes and relatively stable, slow-changing temperatures (Costello & Chaudhary, 2017). Yet, and despite this enormous habitat availability and the fact that life has evolved for a longer time in the sea, only 16% of described species on Earth are marine species [START_REF] Costello | Global coordination and standardisation in marine biodiversity through the World Register of Marine Species (WoRMS) and related databases[END_REF]. With the deep sea representing around 60% of the planet's surface, it is clear that no area encompassing such environments should be seen as closed systems. My results, whether obtained from morphological or molecular studies, show that diversity patterns do not always end where the determined boundaries of the studied area do (Chapter 2 and 3). Incorporating samples and areas from outside the Southern Ocean has proven to be an asset in Chapters 2 and 3 and reinforces the idea of a Southern Ocean that is not so isolated even south of the Polar Front (e.g. [START_REF] Clarke | How isolated is Antarctica?[END_REF].

When integrating molecular approach and the inclusion of surrounding areas, the impact on levels of endemism is straightforward by revealing affinities that were ignored before (Chapter 2 and 3). Using only the morphological approach in the first Chapter, I showed that levels of endemism were lower than previously estimated even though they remain high (59% in the Southern Ocean and 29% south of the Polar Front). Chapter 3 comforted this trend and by revealing novel molecular affinities within and beyond the Southern Ocean suggesting that further work will reduce even more the measured endemism.

Finally, and in accordance with a recent study on 65,000 marine species (Chaudhary et al., 2017) I showed that there is no evidence for a diversity gradient decreasing the polewards for sea stars (Chapter 3). This general pattern has dominated theoretical discussions and analyses but is based on terrestrial systems where solar energy influx seems to drive diversity [START_REF] Valentine | A twofold role for global energy gradients in marine biodiversity trends[END_REF] while this is less evident in marine systems. This last point brings an additional argument regarding the underestimated diversity at high latitudes.

c. Biogeographic processes in the Southern Ocean

The observed patterns of distribution and diversity result from a variety of ecological and evolutionary processes shaping and explaining them [START_REF] Saucède | Biogeographic processes in the Southern Ocean. Biogeographic Atlas of the Southern Ocean[END_REF]. Speciation, extinction, adaptation followed by radiation and dispersal all played a role and led to the distinctiveness of Southern Ocean life [START_REF] Rogers | Evolution and biodiversity of Antarctic organisms: a molecular perspective[END_REF][START_REF] Pearse | Brooding and species diversity in the Southern Ocean: selection for brooders or speciation within brooding clades? Smithsonian at the poles: contributions to international polar year science[END_REF], Krug et al., 2010).

Tectonic and oceanographic factors, through geomorphology (geographic isolation, deep-sea surroundings), and the setting up of marine fronts and currents have notably contributed to the partial isolation and endemism of the Antarctic marine benthos including sea stars (Chapter 1 and 3; [START_REF] Marques | Areas of endemism in the Antarctic-a case study of the benthic hydrozoan genus Oswaldella (Cnidaria, Kirchenpaueriidae)[END_REF]. On the other hand, the Antarctic Circumpolar and Coastal Currents have played a homogenising role explaining circumpolar distribution patterns at the scale of the entire Southern Ocean or at lower scales (Chapter 1, 2 and 3, [START_REF] Moore | The Antarctic Circumpolar Current isolates and connects: Structured circumpolarity in the sea star Glabraster antarctica[END_REF][START_REF] Hemery | Comprehensive sampling reveals circumpolarity and sympatry in seven mitochondrial lineages of the Southern Ocean crinoid species Promachocrinus kerguelensis (Echinodermata)[END_REF]. Endemism has also been reinforced by insitu extinction, adaptation and speciation events (see [START_REF] Dayton | 12 Polar Benthos[END_REF] that were conditioned by climatic changes of the Cenozoic. Glacial temperatures clearly promoted the expansion of certain taxa through adaptation and radiation (e.g glycoproteins in notothenioid fishes) and conversely, the extinction of taxa that did not adapt to the cooling (e.g. durophagous predators). Until now, there is no evidence of adaptive radiation at the origin of Southern Ocean sea stars, and results of this thesis rather suggest an ecological success of the group due to the wide ecological niche of most species (Chapter 3). The climatic history of the Southern Ocean can however not only be summarised by the "global Cenozoic cooling". The 38 Pliocene-Pleistocene glacial cycles that occurred over the last 5 Myr [START_REF] Naish | Obliquity-paced Pliocene West Antarctic ice sheet oscillations[END_REF] also impacted habitats and life in the Southern Ocean. Glacial cycles leading to population fragmentations may have had a tremendous effect on in situ diversification by promoting speciation following the "Antarctic diversity pump" hypothesis proposed by [START_REF] Clarke | The Southern Ocean benthic fauna and climate change: a historical perspective[END_REF]; Chapter 2 and 3) but also probable extinctions [START_REF] Krug | Signature of the end-Cretaceous mass extinction in the modern biota[END_REF]. The numerous and recent diversification events suggested in our time-calibrated phylogeny, leading to species complexes can certainly be explained by these recent glacial cycles (Chapter 2 and 3). The hypothetical collapse [START_REF] Bamber | Reassessment of the potential sea-level rise from a collapse of the West Antarctic Ice Sheet[END_REF][START_REF] Pollard | Modelling west Antarctic ice sheet growth and collapse through the past five million years[END_REF] of the West Antarctic ice sheet, allowing a trans-Antarctic passage between East and West Antarctic was also suggested in our analyses as a potential vicariant event explaining disparities between these two regions (Chapter 1 and 2; [START_REF] Barnes | Faunal evidence for a late Quaternary trans-Antarctic seaway[END_REF][START_REF] Linse | Biodiversity and biogeography of Antarctic and sub-Antarctic mollusca[END_REF][START_REF] Pierrat | Comparative biogeography of echinoids, bivalves and gastropods from the Southern Ocean[END_REF]. This passage has already been suggested using microsatellites data in the octopus Pareledone turqueti [START_REF] Strugnell | Persistent genetic signatures of historic climatic events in an Antarctic octopus[END_REF] but remains to be confirmed with more samples from the East Antarctic and other taxonomic groups.

Finally, the reproductive strategy of sea stars in concert with dispersal vectors have been of particular interest all along the thesis to explain diversity patterns. Overall, brooders account for low fecundity, high survival and a limited dispersal capacity. On the contrary, broadcasters have a high fecundity and a low survival rate of their larvae. However, this link is not always straightforward, notably due the various passive and active dispersal vectors at play in the Southern Ocean (see Chapter 1 and 2; Held, 2014). I showed, in Chapters 1 and 2, the importance of this life history trait on biogeographic and phylogeographic patterns. Its effect in shaping the genetic diversity and species richness has however not been demonstrated (Chapter 2). The constant effect of disturbances of glacial cycles over the last 5

Myr, isolating and reducing population effective size, the enormous size of the Southern Ocean and the numerous islands found there, might explain the lack of clear effect on diversity and richness but needs further investigations.

Interestingly, brooding was first considered as an adaptation to cold temperatures (the "Thorson Rule"; Thorson, 1950) and the many observations of this behaviour in the Southern

Ocean gave arguments to validate this hypothesis for several decades [START_REF] Thomson | Notice of some peculiarities on the mode of propagation of certain echinoderms of the southern seas[END_REF][START_REF] Murray | Notes on the reproduction of certain echinoderms from the Southern Ocean[END_REF]. We can however not deny that many Southern Ocean invertebrates and sea stars display a pelagic phase in their life cycle, raising questions about "Thorson Rule" and the prevalence of brooding behaviour in colder waters. Data regarding ecological traits of asteroid species are sparse but a compiling realised in the framework of my work references 37 asteroid species as brooders against 22 broadcasters (Chapter 1). The fact that brooding is by far easier to observe than the release of pelagic larvae (e.g. spawning induction, pelagic sampling) reinforces the idea that this trait is not dominant in Southern Ocean sea stars and cannot be considered as an adaptation to freezing conditions [START_REF] Poulin | Evolutionary versus ecological success in Antarctic benthic invertebrates[END_REF].

Conclusion & Perspectives Conclusion & Perspectives

This thesis had three main objectives: 1) to characterise distribution patterns of Southern Ocean sea stars at wide spatial scale while considering species reproductive strategy,

2) to study the spatial structure of genetic diversity in clades with contrasting reproductive strategies, and 3) to explore a global phylogeny of the entire class to unravel its putative origin and evolution in the Southern Ocean.

The biogeographical approach (objective 1) relied on the most extensive database developed for this purpose in the Southern Ocean. It allowed me to show that distribution patterns in Southern Ocean sea stars are consistent with other taxonomic groups, underlying a common history, at least partly, for the Southern Ocean benthos. I also highlighted the role of reproductive strategy in the determination of these patterns, proving that this life history trait does have an influence at a large-scale basis and helps in identifying the underlying processes at play.

Complementing this work using a molecular approach on genera with contrasted reproductive strategies (objective 2) brought additional support into the relevance of considering this life history trait in macroecological studies. I showed that reproductive strategy could have conditioned the spatial structure of genetic diversity while not affecting the level of genetic diversity itself. My results also indicate that an in-depth taxonomic revision of the group is fundamentally needed, questioning in the meantime the results from the first objective at species level.

Finally, the analysis of the entire clade class using a barcode library (objective 3) helped to demonstrate the efficiency of such molecular tool in studying large-scale marine systems.

My results indicate recent diversification events (within the last 5 Myr) together with an important discrepancy between current taxonomy and molecular data, the former being the potential cause of the latter. I also propose a main scenario describing the origin of Southern

Ocean sea stars fauna with successive invasions and exchange events between the Southern Ocean and adjacent regions with comparable environmental conditions, during periods of rapid climate change.

The macroecological approach is important to understand how species biogeography was shaped at wide spatial scale and its potential evolution in the future in a fast-changing environment. Overall, my work underlines the need for a more thoughtful use of available data and more comprehensive sampling effort in the Southern Ocean but also in its surrounding regions and especially in the deep sea. Getting a more extended point of view, by sampling novel areas and promoting the use of existing samples, will help understand with higher precision the impact of the evolutionary and ecological processes at play in the Southern Ocean. It will also help to capture with more precision the levels of diversity in the Southern Ocean and refine distribution patterns. Although it is hard to conceive a study at the scale of an entire class and an entire ocean, the use of a few well-targeted species or genera proved to be fruitful. My ambition was to work at these large spatial and taxonomical scales, acknowledging their limits and strengths.

A lot more work remains to be done to fully understand diversity and processes in the Southern Ocean. The advent of high-throughput sequencing methods appears to be a promising solution for this endeavour, but it will require integrative approaches, notably including taxonomic revisions. Future prospects of particular interest include the study of relevant species to answer questions regarding the processes at the origin of the Southern Ocean benthic fauna. In this framework, the genus Bathybiaster appears to be a perfect candidate. High-throughput methods could indeed give important insights in processes such as the polar emergence and sub-Antarctic emergence or on patterns like bipolar or cosmopolitan distributions. On the other hand, brooding species seem ideal to study, with these same tools, the existence and role of the potential trans-Antarctic seaway. Finally, an effort is crucially needed to reconciliate morphology-based and molecular-based identifications by re-examining the specimens used for original descriptions and by universalising the use of barcode libraries and multi-locus phylogenies to delineate species with more certainty.

• Data source and quality control for Southern Ocean Asteroidea

Data were consolidated using biodiversity information systems (biodiversity.aq, Van de Putte et al., 2016;OBIS, IOC 2016 and through the GBIF data portal) and were complemented with additional data from published literature, including original manuscripts, data papers (e.g. [START_REF] Gutt | Asteroids, ophiuroids and holothurians from the southeastern Weddell Sea (Southern Ocean)[END_REF][START_REF] Moles | Distribution patterns in Antarctic and Subantarctic echinoderms[END_REF], and cruise reports. Additional data were obtained from personal communication with Marc Eléaume, Christopher Mah, Vladimir Laptikhovsky and Anna Jażdżewska. The final working dataset was checked with the WoRMS database (WoRMS Editorial Board, 2015) using the Taxon Match Tool in order to match our data with the most up-to-date taxonomy. The database was cleaned up in order to remove all duplicates due to overlapping origins, georeferencing errors and species synonymy or mis-spelling. Only occurrences for specimens identified at the species level were kept in the working database.

• References used to build the database

  in fulfilment of the requirements of the PhD Degree in science (ULB -"Docteur en Science") and in life science (UBFC -"Docteur en Science de la vie") Academic year 2018-2019 Supervisors: Professor Bruno Danis (Université Libre de Bruxelles) Laboratoire de Biologie Marine And Dr. Thomas Saucède (Université Bourgogne Franche-Comté) Biogéosciences Avant-propos Ce doctorat s'inscrit dans le cadre d'une cotutelle entre les universités de Dijon et Bruxelles et m'aura ainsi permis d'élargir mon réseau au sein de la communauté scientifique tout en étendant mes horizons scientifiques. C'est tout d'abord grâce au programme vERSO (Ecosystem Responses to global change : a multiscale approach in the Southern Ocean) que ce travail a été possible, mais aussi grâce aux collaborations construites avant et pendant ce travail. Cette thèse a aussi été l'occasion de continuer à aller travailler sur le terrain des hautes latitudes à plusieurs reprises pour collecter les échantillons et rencontrer de nouveaux collègues. Par le biais de ces trois missions de recherches et des nombreuses conférences auxquelles j'ai activement participé à travers le monde, j'ai beaucoup appris, tant scientifiquement qu'humainement. Remerciements Lorsque vient le temps de faire un faire bilan et de remercier toutes les personnes ayant accompagné ce projet, je ne peux que réaliser que la thèse est le fruit de nombreuses interactions et d'un travail en équipe. Ce travail est l'aboutissement d'un cheminement depuis mon entrée à l'université et l'initiation aux environnements sous-marin et austraux. Il me revient donc de remercier ces différentes personnes en espérant ne pas en oublier. Je remercie en premier lieu le laboratoire de Biologie Marine et son directeur Philippe Dubois de m'avoir accueilli et d'avoir facilité mon intégration au sein de l'ULB dans un lieu et un environnement qui étaient nouveaux pour moi.

  Ma reconnaissance se dirige également vers les membres du laboratoire de Biologie Marine, techniciens et étudiants qui auront rendu la thèse un peu plus sympathique une fois par leur aide et leurs conseils. Je remercie ainsi Phil pour son énergie débordante et son aide d'une grande valeur, dans et en dehors des travaux scientifiques. Merci Mathieu pour ton assistance plus que précieuse en laboratoire qui m'aura permis d'aller au bout de mes analyses. Shukraan Saloua pour toutes les pauses café et ta propension à toujours trouver une solution aux problèmes. Auré et Mishal merci d'avoir accompagné mon parcours à Bruxelles avec la bienveillance et la bonne humeur qui vous caractérise. Merci Antonio pour n'avoir jamais refusé de me donner un coup de main pendant la thèse. Un grand merci aussi à Marine et Mathilde qui auront apporté un vent de fraicheur et de légumes dans le laboratoire pendant ma dernière année de travail. Merci Clément et Laurence pour votre aide technique et administrative. Je remercie également les programmes et instituts qui ont apporté leur soutien au cours de la thèse, me permettant de mener à bien expériences et travaux de terrain : les programmes rECTO et vERSO financés par le Belgian Science Policy Office, le Museum National d'Histoire Naturelle de Paris, le laboratoire Biogéosciences, le programme Ant-ERA et le FRIA (Fonds pour la formation à la Recherche dans l'Industrie et l'Agriculture, FNRS). C'est aussi grâce aux nombreuses personnes et interactions à travers nos différentes collaborations que cette thèse a été menée à bien et notamment Arnaud Brayard du laboratoire Biogéosciences, Elie Poulin et Karine Gérard au Chili, Stefano Schiaparelli de Gênes, Franz et Henrik de la KU Leuven, Patrick Mardulyn et Chantal De Ridder de mon comité d'accompagnement à l'ULB.

FiguresFigure 1 Figure 2 Figure 3 Figure 4 Figure 5

 12345 Figures

Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12

 789101112 Figure 6 A sketch of the Antarctic Circumpolar Current system showing the zonal flow and the meridional overturning circulation and water masses. Antarctica is at the left side. The east-west section displays the isopycnal (same density) and sea surface tilts in relation to submarine ridges, which are necessary to sustain the bottom form stress signatures (see Olbers et al. 2004). The curly arrows at the surface indicate the buoyancy flux; the arrows attached to the isopycnals represent turbulent mixing. An upper cell is formed primarily by northward Ekman transport (horizontal transport of superficial water layers through wind friction) beneath the strong westerly winds and southward transport in the Upper Circumpolar Deep Water (UCDW) layer. The lower cell is driven primarily by formation of dense AABW near the Antarctic continent and inflowing Lower Circumpolar Deep Water (UCDW or NADW). Figure from Olbers and Visbeck (2005), adapted from Speer et al. (2000). ........................................................................................................................... 39

Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure 21 Figure 22 Figure 23 Figure 24 Figure 25 Figure 26 Figure 27

 131415161718192021222324252627 Figure 12 Key stages in the evolution of the Antarctic marine fauna. Seven key events through the Cenozoic era are superimposed on the deep-sea palaeotemperature curve developed by Zachos et al., 2008 and Hansen et al., 2013. It should be noted that shelf-depth palaeotemperatures do not necessarily track those of the deep-sea precisely. The trajectory of Antarctic taxonomic diversity through the Cenozoic is still imperfectly known, but it may not bear any close similarity to either the shallow-or deep-sea palaeotemperature curves. Symbols: ACC, Antarctic Circumpolar Current, K, Cretaceous, Pl., Pliocene, P., Pleistocene .Figure from Crame, 2018. ......................................... 46

Figure 3

 3 Figure 3 Global deep-sea oxygen isotope and temperature records during the last 50 Myr (Zachos et al., 2001) showing the Antarctic Cryosphere History (A.C.H.) major geologic (G), climatic (C), oceanographic (O) events. Modified from González-Wevar et al., 2017.

Figure 4

 4 Figure 4 Major Southern Ocean circulation features (adapted from Rintoul et al. 2001), showing the Polar and sub-Antarctic Fronts of the Antarctic Circumpolar Current, sub-polar gyres and Antarctic Slope Front (ASF). Background colours show bathymetry. Figure from Post et al., 2014.

Figure 5

 5 Figure 5 The globe viewed on a Spilhaus projection; in contrast to conventional projections, this portrays the ocean fringed by land. The global thermohaline circulation is shown in cartoon form, with upper-layer flow in red and lower-layer flow in blue. Figure from Meredith, 2019.

  Figure 6 A sketch of the Antarctic Circumpolar Current system showing the zonal flow and the meridional overturning circulation and water masses. Antarctica is at the left side. The eastwest section displays the isopycnal (same density) and sea surface tilts in relation to submarine ridges, which are necessary to sustain the bottom form stress signatures (see Olbers et al. 2004). The curly arrows at the surface indicate the buoyancy flux; the arrows attached to the isopycnals represent turbulent mixing. An upper cell is formed primarily by northward Ekman transport (horizontal transport of superficial water layers through wind friction) beneath the strong westerly winds and southward transport in the Upper Circumpolar Deep Water (UCDW) layer. The lower cell is driven primarily by formation of dense AABW near the Antarctic continent and inflowing Lower Circumpolar Deep Water (UCDW or NADW). Figure from Olbers and Visbeck (2005), adapted from Speer et al. (2000).

Figure 8

 8 Figure 8 Environmental changes over the industrial period and the 21 st century for businessas-usual scenario and a stringent emissions scenario consistent with the UNFCCC target of increase in global surface temperature by 2°C. (A to E) Changes in globally averaged (A) Sea surface temperature (SST), (B) sea level, (C) sea surface pH (total pH scale), (D) ocean volume (in % of total ocean volume) with saturation state of calcium carbonate in aragonitic form (Wa) above 1 and above 3, and (E) dissolved oxygen. RCP8.5, red lines; RCP2.6, blue lines. Maps show the 21st century changes in SST (F and G) and in sea surface pH (H and I) for RCP8.5 (top) and RCP2.6 (bottom), respectively. All projected values represent ensemble mean values from the Coupled Model Intercomparison Project 5. Figure from Gattuso et al., 2015.

Figure 9

 9 Figure 9 Relationships between changes in the living and non-living nature of the Southern Ocean, depicted in a condensed and simplified way. Arrows indicate directed impact. Interactions between biota and the environment are depicted in red. Links within ecosystem components are only very coarsely considered. Figure from Gutt et al., 2015. For description of individual links see Data S1 in Gutt et al., 2015.

Figure 10

 10 Figure 10 Schematic representation of ice sheet balance in Antarctica from 1979 to 2017. Figure by Amanda Montañez, adapted from Rignot et al., 2019.

Figure 11

 11 Figure 11 Antarctica and the Southern Ocean in 2070, under 'low emissions/high action' (left) and 'high emissions/low action' (right) scenarios. Figure from Rintoul et al., 2018.

Figure 12

 12 Figure12Key stages in the evolution of the Antarctic marine fauna. Seven key events through the Cenozoic era are superimposed on the deep-sea palaeotemperature curve developed by[START_REF] Zachos | An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics[END_REF][START_REF] Hansen | Climate sensitivity, sea level and atmospheric carbon dioxide[END_REF] It should be noted that shelf-depth palaeotemperatures do not necessarily track those of the deep-sea precisely. The trajectory of Antarctic taxonomic diversity through the Cenozoic is still imperfectly known, but it may not bear any close similarity to either the shallow-or deep-sea palaeotemperature curves. Symbols: ACC, Antarctic Circumpolar Current, K, Cretaceous, Pl., Pliocene, P., Pleistocene .Figure from[START_REF] Crame | Key stages in the evolution of the Antarctic marine fauna[END_REF]

  99 and notably including the Discovery and Pourquoi-Pas? research voyages (Figure14).

Figure 13

 13 Figure 13 Seasonal variation in the Antarctic sea-ice cover (October and February 2015-2016). NASA Earth Observatory maps by Joshua Stevens, using AMSR2 data supplied by GCOM-W1/JAXA.

Figure 15

 15 Figure 15 The relative distribution of Southern Ocean (a) benthic sampling intensity (mean = 800 m, median = 4,050 m), (b) pelagic sampling intensity (mean = 120 m, median = 2,950 m) and (c) seafloor area with depth (mean = 3,460 m, median = 4,150 m). Red line indicates the 1000 m depth (shelf break), blue line indicates the 3,000 m depth (abyssal plain).

Figure 17

 17 Figure 17 From left to right. Specimens of sea star, sea urchin and brittle star brooding juveniles. Credits: National Museum of Natural History, Smithsonian Institution; P. Bucktrout, British Antarctic Survey and P.J. López-González.

Figure 18

 18 Figure 18 Current competing hypothesis of relationships derived from morphological or molecular data for the major sea star's clades (Figure from Feuda & Smith, 2015).

Figure 19

 19 Figure 19 Illustration of the Southern Ocean sea stars diversity from the Belgica121 expedition. From top left to bottom right: Granaster nutrix, Labidiaster annulatus, Psilaster charcoti, Odontaster validus, Lysasterias sp. and Neosmilaster georgianus. Photo credits Quentin Jossart.

Figure 20

 20 Figure 20 Occurrences of RAMS (light grey dots) and Proposed-RAMS (orange dots) sea star species. The Antarctic zone is located below the green line and the Sub-Antarctic zone between the green and dark red lines. The Polar Front (black line) and the Sub-Tropical Front (dashed black line) are also shown.

  Compiled occurrenceswere complemented with data from personal communications of unpublished works and museums registered collections. This extensive dataset was developed to describe distribution patterns in the Southern Ocean as well as faunal affinities among 25 Antarctic and Sub-Antarctic bioregions (see[START_REF] Moreau | Reproductive strategy as a piece of the biogeographic puzzle: a case study using Antarctic sea stars (Echinodermata, Asteroidea)[END_REF]. Several analytical methods such as Bootstrap Spanning Network, non-metrical multidimensional scaling (nMDS) and clustering contributed to highlight the importance of the reproductive strategy on the contemporary observed distribution patterns. The importance of environmental parameters such as influence of Antarctic Circumpolar Current, the influence of the Polar Front, the presence of gyres or the geographic distance among locations has also been emphasised. This dataset helped to better describe the different biogeographic patterns within asteroids, which are overall congruent with other taxa and differs according to species reproductive strategy. This suggests a differential influence of dispersal capabilities on species distribution patterns. Analyses at genus levels also revealed the underlying legacy of past oceanographic and geodynamic processes in present-day patterns such as the existence of a trans-Antarctic pathway that split the Antarctic continent into two entities in the past. The detailed results are available from[START_REF] Moreau | Reproductive strategy as a piece of the biogeographic puzzle: a case study using Antarctic sea stars (Echinodermata, Asteroidea)[END_REF].

  with 13,840 occurrences gathered from various sources. The time coverage of the collection starts in 1872 with the HMS Challenger expedition and ends in 2016 with sampled collected during the RRS James Clark Ross JR15005 SO-AntEco cruise. Associated to occurrence data, depth, relative position to the Polar Front, taxonomic information and bioregion were implemented when available. Depth data were extracted from www.gebco.net. Information regarding the reproductive strategy (brooding or broadcasting) of 63 species out of the 299 described was included in the database. Corresponding bioregions of the observed occurrences were specified following Moreau et al., 2017. A significant part of the specimens is deposited in various institutions: e.g., National Museum of Natural History (NMNH), Museum national d'Histoire naturelle (MNHN), Museo Nazionale dell'Antartide (MNA), Université Libre de Bruxelles (ULB), Museo Argentino de Ciencias Naturales (MACN), National Institute of Water and Atmospheric Research (NIWA).Quality control description:Data are available at species level. Nomenclature was thoroughly checked using the Taxon Match Tool implemented in the World Register of Marine Species(WoRMS Editorial Board, 2016), to delete all potential discrepancies and update the taxonomy determination. All replicates originating from overlapping origins as well as errors regarding the georeferencing, species synonymy, or misspelling were removed. Most of the occurrences additions originating from recent campaigns were identified by Christopher Mah and Camille Moreau.

  Indeed, considerable parts of the Southern Ocean present a crucial lack of sampling. In the context of this study, richness values and sampling effort present a significant positive correlation in space (Pearson r = 0.52, p < 0.001) indicating the need to extend the development of this unique synthesis work and to strengthen the effort for other taxonomic groups.

Figure 21

 21 Figure 21 Map of the 13,840 asteroid species occurrences available in the present database, within the boundaries of the Southern Ocean (45°S). Projection: South Pole Stereographic.

Figure 22 Format

 22 Figure 22 Species richness in the Southern Ocean. The number of asteroid species present in 1° × 1° grid cells are reported using yellow-red colour chart B Sampling effort in the Southern Ocean for the class Asteroidea. The number of sampling station per 1° × 1° grid cell is reported using yellow-red colour chart. Projection: South Pole Stereographic.

  of abyssal basins surrounding the Antarctic continent, have resulted in the biogeographic isolation of the Antarctic shelf, especially the benthos (see[START_REF] Clarke | How isolated is Antarctica?[END_REF]. The combined impacts of surface currents, the environmental characteristics of the Southern Ocean and the long-term gradual cooling and past glacial-interglacial cycles occurring during the Plio-Pleistocene have driven biogeographic patterns[START_REF] González-Wevar | Divergence time estimations and contrasting patterns of genetic diversity between Antarctic and southern South America benthic invertebrates[END_REF][START_REF] Strugnell | Persistent genetic signatures of historic climatic events in an Antarctic octopus[END_REF]. The development of the Antarctic Circumpolar Current during the Eocene/Oligocene has and continues to play a major role in the circum-Antarctic structure of environmental and biotic patterns by initiating a fast, clockwise transport of water, dispersing propagules around

Figure 23 )

 23 Figure 23): Adélie Land (ALand); Antarctic Peninsula & the South Shetland Is. (AP&SSh); Amundsen & Bellingshausen Sea (AS&BS); Balleny & Scott Is. (Bal&Sco); Bounty & Antipodes Is. (Bount&Ant); Bouvet Is. (Bouv); Campbell & Auckland Is. (Cam&Auc); Crozet Is. (Cro); Davis Sea & Wilkes Land (DS&WL); Falkland Is. (Fal); Heard Is. (Heard); Kerguelen Is. (Ker); Macquarie Is. (Mac); Ob & Lena seamounts (Ob&Lena); Prydz Bay (PBay); Prince Edward & Marion Is. (PEd&Mar); Queen Maud Land & Enderby Land (QML&EL); Ross Sea (Ross); South Argentina (SArg); South Chile (SChi); South Georgia & Shag Rocks (SG&Sha); South Orkney Is. (SOrk); South Sandwich Is. (SSand); Tierra Del Fuego (TdF) and Weddell Sea (WS).

Figure 23

 23 Figure 23 Map of the Southern Ocean. Area of study (below 45 °S) showing the bioregions: Adélie Land (ALand); Antarctic Peninsula & the South Shetland Is. (AP&SSh); Amundsen & Bellingshausen Sea (AS&BS); Balleny & Scott Is. (Bal&Sco); Bounty & Antipodes Is. (Bount&Ant); Bouvet Is. (Bouv); Campbell & Auckland Is. (Cam&Auc); Crozet Is. (Cro); Davis Sea & Wilkes Land (DS&WL); Falkland Is. (Fal); Heard Is. (Heard); Kerguelen Is. (Ker); Macquarie Is. (Mac); Ob & Lena seamounts (Ob&Lena); Prydz Bay (PBay); Prince Edward & Marion Is. (PEd&Mar); Queen Maud Land & Enderby Land (QML&EL); Ross Sea (Ross); South Argentina (SArg); South Chile (SChi); South Georgia & Shag Rocks (SG&Sha); South Orkney Is. (SOrk); South Sandwich Is. (SSand); Tierra Del Fuego (TdF) and Weddell Sea (WS). Depth of study, between 0 and 1500 m is shown in light grey. Projection: South Pole stereographic.

  from 16 stations for both Queen Maud Land & Enderby Land (QML&EL) and Ob & Lena seamounts (Ob&Lena) to 993 stations for Campbell and Auckland Is. (Cam&Auc) (Table2). Similar patterns can be observed for the number of occurrences [from 45 in the Davis Sea & Wilkes Land (DS&WL) to 2,259 in the Weddell Sea (WS)] and the richness at any taxonomic level (the number of orders, families, genera and species ranges from 4 to 7, 9 to 20, 14 to 61, 20 to 128 respectively). Species accumulation curves for each bioregion (Figure24a, b) indicate that bioregions Cam&Auc, Ker and Ross are the only ones reaching an asymptote and that many species remain to be discovered in the Southern Ocean regardless of the location.

  Among the 196 species found south of the Polar Front, 56 are restricted to the Antarctic zone (c. 29% endemism). In our dataset, 66 species (c. 22%) are only found around southern New Zealand and the adjacent regions (Chatham Islands, Tasmania), but not in any other region of the Southern Ocean. At the scale of a bioregion endemism is low, varying from zero to four endemic species.

Figure 24

 24 Figure 24 Accumulation curves at the species level of Asteroidea for each investigated bioregion: Adélie Land (ALand); Antarctic Peninsula & the South Shetland Is. (AP&SSh); Amundsen & Bellingshausen Sea (AS&BS); Balleny & Scott Is. (Bal&Sco); Bounty & Antipodes Is. (Bount&Ant); Bouvet Is. (Bouv); Campbell & Auckland Is. (Cam&Auc); Crozet Is. (Cro); Davis Sea & Wilkes Land (DS&WL); Falkland Is. (Fal); Heard Is. (Heard); Kerguelen Is. (Ker); Macquarie Is. (Mac); Ob & Lena seamounts (Ob&Lena); Prydz Bay (PBay); Prince Edward & Marion Is. (PEd&Mar); Queen Maud Land & Enderby Land (QML&EL); Ross Sea (Ross); South Argentina (SArg); South Chile (SChi); South Georgia & Shag Rocks (SG&Sha); South Orkney Is. (SOrk); South Sandwich Is. (SSand); Tierra Del Fuego (TdF) and Weddell Sea (WS). (a) Close-up of the first 250 stations. (b) Complete dataset.

Figure 25

 25 Figure 25 Cluster analyses (average linkage) of the percentage faunal similarity (a), (c), (e) and (g) using the Bray-Curtis index and bootstrapped spanning networks (b), (d), (f) and (h) performed for species and genus level as well as for brooding and broadcasting species for the class Asteroidea among the studied bioregions: Adélie Land (ALand); Antarctic Peninsula & the South Shetland Is. (AP&SSh); Amundsen & Bellingshausen Sea (AS&BS); Balleny & Scott Is. (Bal&Sco); Bounty & Antipodes Is. (Bount&Ant); Bouvet Is. (Bouv); Campbell & Auckland Is. (Cam&Auc); Crozet Is. (Cro); Davis Sea & Wilkes Land (DS&WL); Falkland Is. (Fal); Heard Is. (Heard); Kerguelen Is. (Ker); Macquarie Is. (Mac); Ob & Lena seamounts (Ob&Lena); Prydz Bay (PBay); Prince Edward & Marion Is. (PEd&Mar); Queen Maud Land & Enderby Land (QML&EL); Ross Sea (Ross); South Argentina (SArg); South Chile (SChi); South Georgia & Shag Rocks (SG&Sha); South Orkney Is. (SOrk); South Sandwich Is. (SSand); Tierra Del Fuego (TdF) and Weddell Sea (WS). Links with BSV < 70% correspond to dashed lines, links with BSV < 50% are not shown. Corresponding groups based on the cluster analyses display a similar colour. Green: New Zealand -Red: South America -Orange: Sub-Antarctic Islands -Blue: High Antarctica or East Antarctica -Purple: West Antarctica -Burgundy: Circumpolar Pattern.

  , b): (I) the New Zealand province, composed of Bount&Ant and Cam&Auc bioregions (SP = 6% only with the closest bioregions); (II) South America and the sub-Antarctic Islands(SChi, SArg, Fal, Heard, Ker, Ob&Lena, Cro, PEd&Mar), and is separated from the third group at SP = 36%; and (III) Antarctic bioregions(Bal&Sco, Bouv, PBay, Aland, Ross, AP&SSh, WS, SG&Sha, SOrk, SSand, QML&EL, DS&WL and TdF). Cluster analyses indicate that groups II and III can be subdivided into smaller geographic entities: South America (IIa) and the sub-Antarctic Islands (IIb) (SP = 38%), East Antarctica (bioregions east of the prime meridian, including Ross) (IIIa) and West Antarctica (bioregions west of the prime meridian) (IIIb) (SP = 52%) respectively. Potential faunal connections among these entities are highlighted by the BSN analysis (See Appendix 1 for BSV) (Figure25b). East and West Antarctica are well connected to each other through a particularly strong link between the Weddell (WS) and Ross Seas (BSV = 100%), however no link between WS and the closest other bioregions of East Antarctica is observed. West Antarctica and South America are connected to each other through TdF (BSV = 99.9%). South America shows a strong link with the sub-Antarctic Islands (BSV = 99.8%). Within the sub-Antarctic group, the link is weak (BSV = 63%) between Macquarie and other sub-Antarctic Islands. The nMDS analysis allows visualising similarities among bioregions with a low stress value (0.08). The minimum spanning tree (MST) plotted on the graph indicates the shortest path between bioregions (Figure 26a, b) and confirms that bioregions from New Zealand are well differentiated from others. Two other bioregions, AS&BS and Mac, are also well discriminated. Other bioregions (Figure 26b) are plotted together following a north-south differentiation: sub-Antarctic and South American bioregions on one side, Antarctic bioregions and the Scotia Arc on the other, with the exception of Tierra del Fuego that shows affinities with Antarctic bioregions (note the shortest path between TdF and SOrk).

Figure 26

 26 Figure 26 Non-metric multidimensional scaling map with superimposed minimum spanning tree (partial representation to ease the reading) for the class Asteroidea among the 25 studied bioregions: Adélie Land (ALand); Antarctic Peninsula & the South Shetland Is. (AP&SSh); Amundsen & Bellingshausen Sea (AS&BS); Balleny & Scott Is. (Bal&Sco); Bounty & Antipodes Is. (Bount&Ant); Bouvet Is. (Bouv); Campbell & Auckland Is. (Cam&Auc); Crozet Is. (Cro); Davis Sea & Wilkes Land (DS&WL); Falkland Is. (Fal); Heard Is. (Heard); Kerguelen Is. (Ker); Macquarie Is. (Mac); Ob & Lena seamounts (Ob&Lena); Prydz Bay (PBay); Prince Edward & Marion Is. (PEd&Mar); Queen Maud Land & Enderby Land (QML&EL); Ross Sea (Ross); South Argentina (SArg); South Chile (SChi); South Georgia & Shag Rocks (SG&Sha); South Orkney Is. (SOrk); South Sandwich Is. (SSand); Tierra Del Fuego (TdF) and Weddell Sea (WS). (a) All bioregions. (b) Close-up without AS&BS, Mac, Cam&Auc and Bount&Ant.

  indicates five groups: (I) Ob & Lena seamounts (Ob&Lena) and the South Sandwich Island (SSand) (SP = 22% with the remaining groups); (II) sub-Antarctic Islands (Ker, Heard, Cro and PEd&Mar) (SP = 24% with the remaining groups); (III), four New Zealand, sub-Antarctic and Antarctic bioregions (Cam&Auc, Bal&Sco, Bouv and DS&WL); (IV) eight Antarctic bioregions (SP = 40% between group III and IV) differ from the fifth group; and (V) South American bioregions (SChi, Fal, SArg and TdF) at SP = 30%. The Antarctic group is subdivided into two subgroups: high Antarctica (IVa) (WS, PBay, Aland and Ross) and West Antarctica (IVb) (SG&Sha, AP&SSh and SOrk) (SP = 59%). BSN connections (Figure 25f) indicate the occurrence of a link between New Zealand and Balleny & Scott Is. (Bal&Sco) (BSV = 86%) as well as strong affinities among all bioregions of the high Antarctica (continental Antarctica excluding the Antarctic peninsula). South America is strongly linked to the West Antarctica to the south and the sub-Antarctic Islands to the east through South Georgia & Shag Rocks (SG&Sha) (BSV = 98.5% and 85.7% respectively).

  For example, González-Wevar et al. (2012) used the COI marker in various taxa (Sterechinus, Nacella and Yoldia) to demonstrate that the barrier between Antarctic and sub-Antarctic areas formed 3.7 to 5 Mya. This barrier reflects the recent impact of Plio-Pleistocene glaciations more than the ancient oceanographic history of the Antarctic Circumpolar Current. Janosik et al. (2011) drew a similar conclusion using data on asteroids, and proposed that mixing was still possible during the Last Glacial Maximum (21,000 years ago) due to changing and moving boundaries of the Polar Front. In contrast, the molecular phylogeny of the sea star superorder Valvatacea (Mah & Foltz, 2011a) suggests a possible ancestry of the Antarctic fauna from the adjacent sub-Antarctic regions and a diversification of the Antarctic Asteriidae associated with the isolation of the Southern Ocean fauna and the formation of the Antarctic Circumpolar Current. Another molecular study on the asteroid superorder Forcipulatacea (Mah & Foltz, 2011b) also supports the hypothesis of diversification of Antarctic clades when the Antarctic Circumpolar Current first started to flow.

Figure 27

 27 Figure 27 Maps of the Southern Ocean indicating sample location for each target group (red stars). Sampling locations are labelled: red -South Georgia; pink -South Sandwich Islands; yellow -Bouvet Island; dark blue -Kerguelen Islands; light blue -East Antarctica; light green -Amundsen Sea; orange -Antarctic Peninsula; dark green -Burdwood Bank and purple -Weddell Sea. Projection: South Pole Stereographic.

  using a partition for each codon position as specified by PartitionFinder v2, a strict clock model with a lognormal prior for "clock.rate" such that the median reflected a universal divergence time of echinoderm COI of 3.1 to 3.5% per Myr (McCartney et al., 2000), a Markov chain Monte Carlo run of 20 x 106 generations sampling every 1000 trees and a Yule process speciation prior. The XML file was used through the software BEAST v1.8.4 on the CIPRES Science Gateway (Miller et al., 2010) to reconstruct timecalibrated trees. Tracer v1.6 allowed us to ensure an appropriate effective sampling size (ESS > 200) as recommended by the software documentation. TreeAnnotator v1.8

  Psilaster specimens collected outside the Southern Ocean (Psilaster acuminatus from New Zealand and Australia, Psilaster andromeda from Sweden and Psilaster pectinatus from the Arctic Ocean) are retrieved as monophyletic in a sister clade to Bathybiaster. The monophyly of each brooding genus is supported but one sub-clade only matches with the morphological taxonomy: the species D. meridionalis. All other sub-clades are composed of specimens belonging to distinct morphospecies questioning current taxonomy at the species level.Divergence time estimates suggest numerous divergence events both in brooders and broadcasters over the last 5 Myr and particularly, over the last 2.5 Myr (Figure28). Results also indicate that members of the Asteriidae under study diverged from its Pan-tropical outgroup around 21 Myr ago (Appendix 2). Main divergence events (Figure28; Appendix 2) in P. charcoti and Bathybiaster occurred around 1.6 ± 0.8 Myr ago (Node C and D in Figure28).

Figure 28

 28 Figure 28 Bayesian chronograms of partitioned COI sequences derived from the brooding (left) and broadcasting (right) groups of interest. The distribution of uncertainty of node placement is indicated around each of the main nodes. Time scale is expressed in millions of years. Posterior probabilities and bootstrap values are provided under main nodes. No value was indicated if bootstrap was less than 45%. Coloured patches indicate sampling locations. Results for each species delineation method are reported as black bars representing the delineated units.

  Figure 29; Appendix 2) the first entity (Lysasterias sp1) nearly exclusively contains specimens from East Antarctica with one from the Weddell Sea. The second entity (Lysasterias sp2) mainly contains specimens from the Antarctic Peninsula together with one specimen from the South Sandwich Islands and nine from the Weddell Sea. The third entity is mainly composed

Figure 29

 29 Figure 29 Brooders statistical parsimony network indicating genetic relationships with regards to sampling locations. Delineated clades are represented and colour code follows the central map: red -South Georgia; pink -South Sandwich Islands; yellow -Bouvet Island; dark blue -Kerguelen Islands; light blue -East Antarctica; light green -Amundsen Sea; orange -Antarctic Peninsula; dark green -Burdwood Bank and purple -Weddell Sea. Projection: South Pole Stereographic.

Figure 30

 30 Figure 30 Bathybiaster statistical parsimony network indicating genetic relationships with regards to A) sampling geographic locations and B) sampling depths and Kerguelen Island (shallow and deep). Delineated clades are represented and colour code follows the appended legend.

(

  www.rectoversoprojects.be), funded by the Belgian Science Policy Office (BELSPO, contract n°BR/132/A1/vERSO). The authors thank M. Bauwens, R. Downey, C. Guillaumot and H. Christiansen for their important contribution during key steps of this work. The authors would like to thank all the persons and institutes involved in sharing the samples and sequences analysed in this study as well as research programs that made the collection of samples possible. S. Schiaparelli -University and Museum of Genoa; K. Neill -National Institute of Water and Atmospheric Research; H. Griffiths, D. Barnes and K. Linse -British Antarctic Survey; C. Gallut, N. Améziane, N. Vasset, A. Froger, G. Lecointre and A. Dettaï -Museum National d'Histoire Naturelle, Paris; C. Mah -Smithsonian Institution Programs: PROTEKER (IPEV 1044, French LTER ZATA), POKER 2, REVOLTA (IPEV 1124), CEAMARC, ANTFLOCKs, JR144, JR179, JR230, JR262, JR275, JR287, JR15005, ACE -ASCCC

  , Odontasteridae (n=319), Pterasteridae (n=164), Solasteridae (n=207) and Echinasteridae (clade Henricia + Rhopiella; n=156). These clades exhibit the largest available number of sequences, robust phylogenetic groupings, and cover different phylogeographic signatures. Subtrees were extracted from the main phylogenetic tree for specific discussions (see Appendix 3). The ASAP method (http://wwwabi.snv.jussieu.fr/public/asap) with default settings and K80 corrected distances was used to delineate species within the six targeted clades. Antarctic Asteriidae (Diplasterias, Notasterias and Lysasterias), Astropectinidae (Psilaster and Bathybiaster) and Poraniidae (Glabraster) have recently been investigated by[START_REF] Moreau | Is reproductive strategy a key factor in understanding the evolutionary history of Southern Ocean Asteroidea (Echinodermata)?[END_REF] and[START_REF] Moore | The Antarctic Circumpolar Current isolates and connects: Structured circumpolarity in the sea star Glabraster antarctica[END_REF]; results of these studies were included in the present work.

  Figure 31 Latitudinal gradients of sea stars' species and genus richness in the Southern Ocean. A.) Occurrence map with location of

Figure 32 (

 32 Figure 32 (Double page). Bayesian phylogenetic reconstruction of the class Asteroidea based on mtDNA (COI). Nodes posterior probabilities are indicated when superior to 0.5. Coloured squares indicate specimen locations: blue, Southern Ocean; red, outside the Southern Ocean and yellow, from both inside and outside the Southern Ocean. Subgroups used for further analyses are indicated in red (Fully developed tree available in Appendix 3).

  Spatial affinities with regions surrounding the Antarctic Continent are illustrated by several examples. These affinities exist with New Zealand and notably within the clade 'Cheiraster complex' (Figure 33) which encompasses 93 specimens identified as either Cheiraster otagoensis, C. gerlachei, C. monopedicellaris or C. hirsutus. In the family Benthopectinidae, Cheiraster is the sole genus found in the Southern Ocean with two of the delineated clades recorded in Southern Ocean waters (Appendix 3). Members of the species Lophaster furcilliger (Solasteridae) also show affinities between Southern Ocean and New Zealand along the Macquarie trench (Figure 33). Similarly, specimens from the Magellanic area present affinities with South Georgia, the Kerguelen Islands (e.g. Odontaster penicillatus and Odontaster sp; see Figure 33; Appendix 3) and also Antarctic islands like the Balleny Islands (e.g. Acodontaster sp; see Figure 33; Appendix 3), following a sub-Antarctic circumpolar pattern. Circumpolarity is also observed in other delineated species, either at the scale of the entire Southern Ocean (e.g. Glabraster antarctica, Figure 33) or at finer scale, on the Antarctic shelves (South of 60°S; e.g. Bathybiaster loripes and Cuenotaster involutus).

Finally, species withFigure 33 ;

 33 Figure33; Appendix 3) suggesting recent or ongoing exchange with the northern hemisphere.

  Figure 33 Characteristic phylogeographic signatures of Southern Ocean sea stars shown as parsimony networks of COI

  l'Agriculture" (FRIA) grant to C. Moreau. This is contribution no. 37 to the vERSO project (www.rectoversoprojects.be), funded by the Belgian Science Policy Office (BELSPO, contract n°BR/132/A1/vERSO). The authors would like to thank all the persons and institutes involved in sharing the samples and sequences analysed in this study as well as research programs that made the collection of samples possible. S. Schiaparelli -University and Museum of Genoa; K. Neill -National Institute of Water and Atmospheric Research; H. Griffiths, D. Barnes and K. Linse -British Antarctic Survey; C. Gallut, N. Améziane, N. Vasset, A. Froger, G. Lecointre and A. Dettaï -Museum National d'Histoire Naturelle, Paris; C. Mah -Smithsonian Institution Programs: PROTEKER (IPEV 1044, French LTER ZATA), POKER 2, REVOLTA (IPEV 1124), CEAMARC, ANTFLOCKs, JR144, JR179, JR230, JR262, JR275, JR287, JR15005, ACE -ASCCC

Figure 34

 34 Figure 34 Accumulation curve of Southern Ocean sea stars occurrences available through time (1872-2014) with indication of major international research programs. Data from Moreau et al., 2018.

Figure 35

 35 Figure 35 Number of occurrence records for sea stars (from 1919 to 2019) available from the Ocean Biogeographic Information System.

••

  Phylogenetic trees and Statistical Parsimony networks Bayesian phylogenetic reconstructions and statistical Parsimony network indicating genetic relationships among sampling locations within the families of interest. Time scale is expressed in millions of years. SO: Southern Ocean; N-Atl: North Atlantic Ocean; N-Pac: North Pacific Ocean; NZ: New Zealand; Arctic: Arctic Ocean; S-Atl: South Atlantic • Accumulation curves Accumulation curves at the species level of Asteroidea for the Southern Ocean fitted to match with latitude (UGE index -999 permutations representing a random accumulation curve, SObsrecorded richness according to latitude, Jacknife2 -corrected richness based on sampling effort). Global phylogenetic tree Bayesian phylogenetic reconstruction of the class Asteroidea based on mtDNA (COI). Nodes posterior probabilities are indicated when superior to 0.5. Coloured squares indicate specimen locations: blue, Southern Ocean; red, outside the Southern Ocean and yellow, from both inside and outside the Southern Ocean. Subgroups used for further analyses are indicated in red. Université Bourgogne Franche-Comté 32, avenue de l'Observatoire 25000 Besançon Titre : Diversité et phylogéographie des astéries (Asteroidea) de l'Océan Austral Mots clés : Biogéographie; Echinodermata; Connectivité; Océan Austral; PhylogéographieRésumé : Comment les espèces sont-elles distribuées sur les fonds marins de l'Océan Austral ? Quels sont les facteurs qui peuvent expliquer leur distribution ? Ces questions, centrales en macroécologie sont d'autant plus pressantes que les régions polaires sont actuellement soumises à de rapides changements environnementaux. L'objectif principal de cette thèse était de décrire et de caractériser les grands patrons de distribution des espèces d'étoiles de mer à l'échelle de l'Océan Austral tout en considérant un trait d'histoire de vie en particulier : la stratégie de reproduction. Dans ma thèse, je teste l'hypothèse que les capacités de dispersion contrastées entre espèces à développement direct (incubantes) et celles à stade larvaire pélagique dans leur développement (dispersantes) induisent des motifs de distribution distincts, permettant ainsi de mettre en évidence un facteur déterminant de leurs distributions. J'ai utilisé à la fois des approches biogéographique (basée sur un jeu de données de 14 000 occurrences) et phylogéographique (pour cinq genres : Diplasterias, Notasterias, Lysasterias, Bathybiaster, Psilaster) à l'échelle de l'Océan Austral et mes résultats montrent que 1) de manière générale, les étoiles de mer présentent les mêmes motifs biogéographiques que ceux déjà mis en évidence chez d'autres groupes d'invertébrés marins benthiques tels que l'isolement de la Nouvelle Zélande, la forte richesse spécifique dans la région de l'Arc de la Scotia chez les espèces incubantes, la différenciation entre les faunes Est et Ouest Antarctiques, et les affinités fauniques entre le sud de l'Amérique du Sud et les iles subantarctiques. Les astéries présentent un niveau d'endémisme moins élevé que précédemment avancé, avec 29% d'espèces endémiques dans la Zone Antarctique seulement. Les patrons de distribution sont fortement influencés par la stratégie de reproduction et diffèrent en fonction du niveau taxonomique considéré, mettant en évidence le rôle sous-jacent de certains facteurs historiques. 2) La stratégie de reproduction ne semble pas affecter les niveaux de diversité génétique ni la richesse spécifique elle-même mais plutôt leur structuration spatiale. L'histoire évolutive des espèces est le résultat de leur stratégie de reproduction. Les patrons phylogéographiques des espèces dispersantes peuvent être expliqués par différents scénarios impliquant des voies de colonisation profondes, de la bipolarité ou du cosmopolitisme, et l'émergence en zone subantarctique pour le genre Bathybiaster ; des échanges fauniques entre Antarctique et Nouvelle Zélande à travers le Front Polaire pour le genre Psilaster. Les motifs présentés par les espèces incubantes suggèrent l'existence d'un passage trans-antarctique précédemment étendu entre les mers de Ross et de Weddell pendant le Plio-Pléistocène. Ces résultats mettent aussi en évidence, pour la première fois, que la Mer de Weddell est peuplée d'un mélange de faunes originaires d'Est et Ouest Antarctique. Enfin, j'utilise une approche exploratoire pour analyser la phylogénie et la phylogéographie de toute la classe des Asteroidea afin de comprendre son origine et son évolution dans l'Océan Austral. Je mets en évidence la variété des chemins évolutifs suivis par les étoiles de mer pour coloniser, se diversifier et évoluer dans l'Océan Austral. Je démontre par la même occasion que leur richesse spécifique n'est pas correctement évaluée dans l'Océan Austral, ce qui est également très certainement le cas aussi dans les autres océans. Je démontre aussi que la diversité des étoiles de mer australes actuelles est en grande partie le résultat de diversifications récentes. L'ensemble de ces résultats m'amène à remettre en question plusieurs grands principes biogéographiques jusqu'ici reconnus pour les faunes de l'Océan Austral, soulignant également la nécessité d'adopter des approches à très large échelle dans ce genre d'étude. Title: Diversity and phylogeography of Southern Ocean sea stars (Asteroidea) Keywords: Biogeography; Echinodermata; Connectivity; Southern Ocean; PhylogeographyAbstract : How is life distributed on the Southern Ocean sea floor? How can we explain species distribution patterns, their origin and the underpinning drivers? These questions are central to macroecological studies, especially in regions facing fast environmental changes. The main objective of this thesis was to describe and characterise distribution patterns of sea stars species (Echinodermata: Asteroidea) with regards to reproductive strategy (i.e. brooding versus broadcasting), a key life history trait for species dispersal. I tested whether contrasting dispersal abilities between direct developers (brooders) and species with pelagic larvae in their development (broadcasters) result in distinct diversity and distribution patterns. At the scale of the Southern Ocean, I used both biogeographic (14,000 occurrence records) and phylogeographic approaches (five genera -Diplasterias, Notasterias, Lysasterias, Bathybiaster, Psilaster) to show that 1) biogeographic patterns are highly linked to reproductive strategy but these patterns also vary according to taxonomic levels, revealing the importance of historical factors. 2) Main biogeographic patterns are congruent with results obtained in previous works for other benthic taxa highlighting the prevalence of common biogeographic patterns like: the isolation of New Zealand fauna from the Antarctic, the high richness in the Scotia Arc region (particularly in brooders), the differentiation between East and West Antarctic species, and faunal affinities between southern South America and sub-Antarctic Islands. Overall, asteroids show low endemism levels compared to previously reported values, with 29% of species only occurring in the Antarctic Zone. 3) Phylogeographic patterns indicate that reproductive strategy is not directly related to the levels of genetic diversity nor to species richness but rather to the spatial structure of species distribution. Phylogeographic patterns analysed in broadcasters can be explained by different scenarios including deep-sea colonisation routes, bipolarity or cosmopolitanism, and sub-Antarctic emergence for the genus Bathybiaster; faunal exchanges between the Antarctic and New Zealand across the Polar Front for the genus Psilaster. Phylogeography of brooders support the hypothesis of a past trans-Antarctic seaway established between the Ross and the Weddell seas during the Plio-Pleistocene. These results also show, for the first time, that the Weddell Sea is composed of a mixed asteroid fauna originating from both the East and West Antarctic. Finally, I use an exploratory approach to investigate the phylogeny and phylogeography of the entire class Asteroidea and try to reveal their origin and evolution in the Southern Ocean. I demonstrate that species richness in asteroids has been overlooked and misunderstood in the Southern Ocean and possibly also all around the world. I then argue that modern Southern Ocean sea star fauna result, for the most part, from recent diversifications. These results, altogether, raise questions about commonly accepted principles on biogeographic patterns in the Southern Ocean. This stresses the need for more global and integrative approaches for such studies.

•

  Sands C.J.*, Barnes, D. K., Downey, R., Moreau, C., Griffiths, H., Linse, K., & Martín-Ledo, R. A pragmatic approach to the assessment of South Georgia benthic diversity reveals a unique and vulnerable assemblage. Scientific Committee on Antarctic Research, XII Biology Symposium, Leuven, Belgium, 07/2017.

• Sands, C.J.*, Downey, R., Held, C., Paulsen, M.,

Barnes

, D.K.A., Moreau, C., Moreno, B., & Bax, N. Towards estimation of blue carbon sink potential of sub-Antarctic continental shelf benthos. Scientific Committee on Antarctic Research, XII Biology Symposium, Leuven, Belgium, 07/2017. • Le Bourg, B.*, Blanchard, A., Danis, B., Jossart, Q., Lepoint, G., Moreau, C., & Michel, L. Influence of environmental conditions on trophic niche partitioning among sea stars assemblages. Scientific Committee on Antarctic Research, XII Biology Symposium, Leuven, Belgium, 07/2017. • Bax, N.*, Moreno, B., Moreau, C., Barnes, D.K., Paulsen, M., Held, C., Downey, R., & Sands, C.J. How important is carbon storage by southern polar benthos as a negative feedback on climate change? Scientific Committee on Antarctic Research, XII Biology Symposium, Leuven, Belgium, 07/2017. • Le Bourg, B.*, Blanchard, A., Danis, B., Lepoint, G., Moreau, C., Jossart, Q., & Michel, L. Feeding ecology of Southern Ocean seastars inferred from stable isotopes ratios. Joint European Stable Isotopes User Group meeting, Ghent, Begium, 09/2016. * Presenting author Table of content 14

Table 1

 1 Bayesian chronograms of partitioned COI sequences derived from the brooding (left) and broadcasting (right) groups of interest. The distribution of uncertainty of node placement is indicated around each of the main nodes. Time scale is expressed in millions of years. Posterior probabilities and bootstrap values are provided under main nodes. No value was indicated if bootstrap was less than 45%. Coloured patches indicate sampling locations. Results for each species delineation method are reported as black bars representing the delineated units. ..................... 131 Bathybiaster statistical parsimony network indicating genetic relationships with regards to A) sampling geographic locations and B) sampling depths and Kerguelen Island (shallow and deep). Delineated clades are represented and colour code follows the appended legend. .................... 136 Figure 31 Latitudinal gradients of sea stars' species and genus richness in the Southern Ocean. A.) Occurrence map with location of both quadrants (New Zealand in green and South America in orange) Projection: South Pole stereographic. B.) Entire Southern Ocean. C.) New Zealand Quadrant. D.) South America Quadrant. Histograms for richness, sampling effort and species:genus ratio are presented by 1° latitudinal bands. Accumulation curves are fitted to match with latitude (UGE index -999 permutations representing a mean random accumulation curve, SObs -recorded richness according to latitude, Jacknife2 -corrected richness based on sampling effort). .......... 155 Figure 32 (Double page). Bayesian phylogenetic reconstruction of the class Asteroidea based on mtDNA (COI). Nodes posterior probabilities are indicated when superior to 0.5. Coloured squares RAMS area of interest. Operational northern limits in the different sector of the Southern Ocean for both the Antarctic zone and the sub-Antarctic zone. ..................................................... 73

	Figure 29 Brooders statistical parsimony network indicating genetic relationships with regards to
	sampling locations. Delineated clades are represented and colour code follows the central map: red

). Sampling locations are labelled: red -South Georgia; pink -South Sandwich Islands; yellow -Bouvet Island; dark blue -Kerguelen Islands; light blue -East Antarctica; light green -Amundsen Sea; orange -Antarctic Peninsula; dark green -Burdwood Bank and purple -Weddell Sea. Projection: South Pole Stereographic. .............................................................................................................. 126 Figure 28 -South Georgia; pink -South Sandwich Islands; yellow -Bouvet Island; dark blue -Kerguelen Islands; light blue -East Antarctica; light green -Amundsen Sea; orange -Antarctic Peninsula; dark green -Burdwood Bank and purple -Weddell Sea. Projection: South Pole Stereographic. ........ 135 Figure 30 indicate specimen locations: blue, Southern Ocean; red, outside the Southern Ocean and yellow, from both inside and outside the Southern Ocean. Subgroups used for further analyses are indicated in red (Fully developed tree available in Appendix 3). ................................................... 158

Figure 33 Characteristic phylogeographic signatures of Southern Ocean sea stars shown as parsimony networks of COI haplotypes coloured according to sampling locations. Species delineation results are presented as red clusters/rectangles for Rhopiella hirsuta. .................................................... 163 Figure 34 Accumulation curve of Southern Ocean sea stars occurrences available through time (1872-2014) with indication of major international research programs. Data from Moreau et al., 2018. ........................................................................................................................................................ 174 Figure 35 Number of occurrence records for sea stars (from 1919 to 2019) available from the Ocean Biogeographic Information System. ............................................................................................... 178 Tables

Table 2

 2 Breakdown numbers of occurrences, stations and taxonomic entities of Asteroidea for each of the 25 investigated bioregions. NA refers to occurrences found outside of the bioregions of interest.

	Adélie Land (ALand); Antarctic Peninsula & the South Shetland Is. (AP&SSh); Amundsen &
	Bellingshausen Sea (AS&BS); Balleny & Scott Is. (Bal&Sco); Bounty & Antipodes Is. (Bount&Ant);
	Bouvet Is. (Bouv); Campbell & Auckland Is. (Cam&Auc); Crozet Is. (Cro); Davis Sea & Wilkes Land
	(DS&WL); Falkland Is. (Fal); Heard Is. (Heard); Kerguelen Is. (Ker); Macquarie Is. (Mac); Ob & Lena
	seamounts (Ob&Lena); Prydz Bay (PBay); Prince Edward & Marion Is. (PEd&Mar); Queen Maud Land
	& Enderby Land (QML&EL); Ross Sea (Ross); South Argentina (SArg); South Chile (SChi); South

Georgia & Shag Rocks (SG&Sha); South Orkney Is. (SOrk); South Sandwich Is. (SSand); Tierra Del Fuego (TdF) and Weddell Sea (WS). ............................................................................................... 108

Table 3 Results of the Mantel test between BSN structure matrices using the Spearman coefficient. rs is the correlation value and p the associated probability. The symbol * underlines significant values (P < 0.05). ....................................................................................................................................... 109 Table 4 Molecular diversity statistics for each delineated species. Statistics for taxonomic groups with n<25 are not represented. n: number of sequences. π: nucleotide diversity. H: haplotype diversity. ........................................................................................................................................................ 132 Table 5 Number of species delineated by the different species delineation methods ...................... 133 Table 6 Sea star richness and endemism estimates (in percentage relative to the global richness) inside and outside the Southern Ocean (Compiled from Mah & Blake, 2012; Moreau et al., 2018). ..... 154 Table 7 Investigated families with mention of their environmental settings (from Mah & Blake, 2012) their presence in the Southern Ocean (SO; from Moreau et al., 2018) and whether genetic sequences are available for the Southern Ocean. Ant: Antarctic (i.e. South of the Polar Front ~60°S; sub-Ant: sub-Antarctic (i.e. North of the Polar Front and south of the Subtropical Front ~45°S). 157

Table 8

 8 Delineated Southern Ocean species in the six investigated clades, with a note regarding the need for a taxonomic revision. Counts based on available genetic sequences. SO: Southern Ocean. ........................................................................................................................................................ 164 Antarctica is the coldest, driest and most isolated continent on Earth. Its position, centred on the South Pole is the result of a long paleogeographic and tectonic history, dating back to as far as the breakup of the supercontinent Gondwana. Initiated at the very end of the Early Jurassic (~175 Ma), this breakup marks the starting point of what will become the Southern

	General Introduction

INTRODUCTION

  Mapping and understanding life diversity are major issues for the community of biologists and ecologists who focus on the Southern Ocean. For several years, many initiatives such as the International Polar Year, the Census of Antarctic Marine Life(CAML 2005(CAML -2010)), the Scientific Committee on Antarctic Research: Marine Biodiversity Information Network (SCAR MarBIN, www.biodiversity.aq) or the Biogeographic Atlas of the Southern Ocean (De Broyer et al., 2014) have also gathered information from distinct and transversal scientific domains to provide new multidisciplinary insights in the study of the Southern Ocean marine ecosystems, linking biogeographic, phylogeographic, physiological, oceanographic, and biogeochemistry data. Such programs have established the most exhaustive and accurate inventories of scientific data ever, since the first historical researches of James Cook in 1772-1775 in the

region, and have provided open source information systems (e.g., Register of Antarctic Marine Species, De Broyer and Danis, 2010; Global Biodiversity Information Facility, http:// www.gbif.org; Ocean Biogeographic Information System http://www.iobis.org/; Van de Putte et al., 2015, http://www.biodiversity.aq).

  Data collected during recent and unpublished campaigns were also added including records from literature, reaching a total of 13,840 occurrences from 4,580 unique sampling events. This dataset represents the most exhaustive database on Antarctic and Sub-Antarctic asteroids.

	PROJECT DESCRIPTION
	Project title: Antarctic and Sub-Antarctic Asteroidea database
	Personnel: Camille Moreau, Charlène Guillaumot, Quentin Jossart, Antonio Agüera,
	Guillaume Crokaert, Marc Eléaume, Thomas Saucède, Katrin Linse, Huw Griffiths, Chester

The present dataset is a compilation of georeferenced occurrences, at species level, for the whole class Asteroidea in the Southern Ocean. Records from 1872 to 2016 have been gathered from various open source databases. Sands, David Barnes, Vladimir Laptikhovsky, Anna Jażdżewska, Jacek Siciński, Noémie Vasset, Lenaïg G. Hemery, Christopher Mah, Nadia Améziane, Stefano Schiaparelli, Bruno Danis Funding: The work was supported by a "Fonds pour la formation à la Recherche dans l'Industrie et l'Agriculture" (FRIA) grants to C. Moreau. This is contribution no. 16 to the vERSO project (http://www.versoproject.be), funded by the Belgian Science Policy Office (BELSPO, contract n°BR/132/A1/vERSO). This is contribution to the IPEV programs n°1124 REVOLTA and n°1044 PROTEKER and to team SAMBA of the Biogeosciences laboratory.

  . Despite this permeability, benthic fauna living south of the Polar Front are highly adapted to polar environmental conditions (e.g.[START_REF] Mcclintock | Trophic biology of Antarctic shallow-water echinoderms. Marine ecology progress series[END_REF][START_REF] Peck | Environmental constraints on life histories in Antarctic ecosystems: tempos, timings and predictability[END_REF] and interactions among all the factors mentioned above have resulted in apparently high levels of endemism in many benthic taxa of the Southern Ocean. The recent Biogeographic Atlas of the Southern Ocean(De Broyer et al., 2014, and chapters herein) estimates 57% endemism for bivalves, 79% for gastropods, 64%

Table 2

 2 Breakdown numbers of occurrences, stations and taxonomic entities of Asteroidea for each of the 25 investigated bioregions. NA refers to occurrences found outside of the bioregions of interest. Adélie Land (ALand); Antarctic Peninsula & the South Shetland Is. (AP&SSh); Amundsen & Bellingshausen Sea (AS&BS); Balleny & Scott Is. (Bal&Sco); Bounty & Antipodes Is. (Bount&Ant); Bouvet Is. (Bouv); Campbell & Auckland Is. (Cam&Auc); Crozet Is.

	(Cro); Davis Sea & Wilkes Land (DS&WL); Falkland Is. (Fal); Heard Is. (Heard); Kerguelen Is.
	(Ker); Macquarie Is. (Mac); Ob & Lena seamounts (Ob&Lena); Prydz Bay (PBay); Prince Edward
	& Marion Is. (PEd&Mar); Queen Maud Land & Enderby Land (QML&EL); Ross Sea (Ross); South
	Argentina (SArg); South Chile (SChi); South Georgia & Shag Rocks (SG&Sha); South Orkney Is.
	(SOrk); South Sandwich Is. (SSand); Tierra Del Fuego (TdF) and Weddell Sea (WS).
	Bioregion	n of occurrences	n of species	n of known brooding species	n of known broadcasting species	n of genera	n of families	n of orders	n of stations
	ALand	694	47	12	14	30	15		141
	AP&SSh	2042	128	25	18	61	20		618
	AS&BS	49	21	7	4	16	9		31
	Bal&Sco	202	34	4	15	28	15		78
	Bount&Ant	245	47	1	2	35	14		149
	Bouv	128	36	6	15	24	10		35
	Cam&Auc	1586	80	3	6	53	19		993
	Cro	489	46	5	9	27	15		118
	DS&WL	45	20	6	7	14	9		26
	Fal	232	47	8	9	31	17		70
	Heard	223	31	6	8	20	14		85
	Ker	1477	52	12	9	31	16		422
	Mac	141	25	5	2	16	13		56
	NA	673	126	NA	NA	73	24		234
	Ob&Lena	68	21	2	8	15	12		16
	PBay	284	44	10	13	31	15		106
	PEd&Mar	106	36	5	7	25	14		29
	QML&EL	111	30	5	9	21	11		16
	Ross	1257	70	12	16	42	18		398
	SArg	154	42	9	5	27	15		63
	SChi	131	38	3	6	30	18		55
	SG&Sha	405	66	17	16	43	19		155
	SOrk	421	68	14	17	45	19		124
	SSand	174	48	5	11	34	17		68
	TdF	409	73	13	12	49	19		178
	WS	2259	101	13	16	51	18		248
	Southern Ocean	14005	299	37	22	118	28		4512

Table 3

 3 Results of the Mantel test between BSN structure matrices using the Spearman coefficient. rs is the correlation value and p the associated probability. The symbol * underlines significant values (P < 0.05).

	Situation	rs	P
	Brooders vs Broadcasters	0.296	0.067
	Brooders vs Genus	0.641*	0.0002
	Broadcasters vs Genus	0.444*	0.0142
	Genus vs Species	0.728*	0.0001

  the isolation of New Zealand from other bioregions of the Southern Ocean and in contrast, strong links between Antarctic bioregions. Bioregions of South America are linked to

	West Antarctic through the South Orkney bioregion (BSV = 98.2%). Sub-Antarctic Islands are
	connected to West Antarctica through South Georgia & Shag Rocks (Sg&Sha; BSV = 86%) to
	the west and to Macquarie Island (BSV = 66%) to the east. A strong circumpolar connection is
	present without the gap observed at species level between the Weddell Sea (WS) and the
	closest other bioregions of East Antarctica (BSV = 99.4%) Figure

  strategies. The influence of New Zealand cold temperate fauna on its southernmost areas is shown by the high level of endemism observed within and around New Zealand waters. The uniqueness of the New Zealand's benthic fauna compared to the rest of the Southern Ocean benthos has been demonstrated in many studies on diverse taxa (e.g. molluscs:Linse et al.,

	2006; bryozoans: Barnes & Griffiths, 2007; and echinoids: Pierrat et al., 2013).
	The faunal affinities between East Antarctica and the Macquarie Island suggest that
	faunal connections may occur through the southern Macquarie ridge, as demonstrated for
	other echinoderms (asteroids and ophiuroids) (O'Hara, 1998; O'Hara et al., 2013). An
	additional link was observed between Macquarie and the sub-Antarctic islands, supporting a
	pattern already established for echinoderms (asteroids, ophiuroids and holothuroids: O'Hara,

Table 4

 4 Molecular diversity statistics for each delineated species. Statistics for taxonomic groups with n<25 are not represented. n: number of sequences. π: nucleotide diversity. H: haplotype diversity.

	Taxonomic group	n	π	n of haplotype	H	Segregating sites	Mean intraspecific distance
	Brooders	Lysasterias sp1	81	0.01000 ± 0.00062	16	0.831 ± 0.027		0.0103 ± 0.0069
		Lysasterias sp2	78	0.01146 ± 0.00093	12	0.840 ± 0.019		0.0118 ± 0.0092
		Lysasterias sp3	56	0.00825 ± 0.00095	13	0.765 ± 0.055		0.0085 ± 0.0073
		Notasterias sp1	236	0.00561 ± 0.00032	23	0.733 ± 0.027		0.0057 ± 0.0044
		Notasterias sp2	80	0.01108 ± 0.00109	14	0.718 ± 0.037		0.0114 ± 0.0096
		Diplasterias sp1	105	0.01262 ± 0.00030	21	0.909 ± 0.013		0.0130 ± 0.0069
		Diplasterias sp2	116	0.01547 ± 0.00097	19	0.849 ± 0.021		0.0161 ± 0.0123
		Diplasterias meridionalis	75	0.00239 ± 0.00023	13	0.777 ± 0.031		0.0024 ± 0.0019
	Broadcasters	Bathybiaster sp1	133	0.00347 ± 0.00042	25	0.790 ± 0.023		0.0035 ± 0.0039
		Bathybiaster sp2	110	0.00557 ± 0.00054	28	0.835 ± 0.026		0.0057 ± 0.0051
		Psilaster charcoti clade1	92	0.01457 ± 0.00069	29	0.924 ± 0.015		0.0151 ± 0.0085
		Psilaster charcoti clade2	55	0.00272 ± 0.00028	12	0.734 ± 0.052		0.0027 ± 0.0020
		Psilaster charcoti clade3 148	0.00160 ± 0.00026	19	0.394 ± 0.052		0.0016 ± 0.0025

Table 5

 5 Number of species delineated by the different species delineation methods

	Taxonomic group		ABGD sGMYC mGMYC mPTP ASAP
	Brooders	Lysasterias	4	17	17	4	4
		Diplasterias	3	14	15	4	3
		Notasterias	3	4	18	3	3
	Broadcasters	Psilaster charcoti	9	9	17	4	9
		Bathybiaster	4	3	12	3	2
	Total		27	47	79	19	30

Table 6

 6 Sea star richness and endemism estimates (in percentage relative to the global richness) inside and outside the Southern Ocean (Compiled from[START_REF] Mah | Taxonomy of high-latitude Goniasteridae (Subantarctic & Antarctic): one new genus, and three new species with an overview and key to taxa[END_REF] Blake 2012, Moreau et al. 2018). *Antarctic refers to waters south of the Polar Front (ca. 60°S); **Doubtful occurrences were removed in line with a conservative approach. Luidia clathrata and Asthenactis australis were excluded as the first one is only known from warm shallow waters and the second from a single specimen at the edge of the Southern Ocean.

		World Ocean	Southern Ocean	Antarctic*
	Taxonomic level	n of taxa	n of taxa	n of endemic	n of taxa	n of endemic
				taxa		taxa
	Order	7	7 (100%)	0 (0%)	7 (100%)	0 (0%)
	Family	38	26** (68%)	0 (0%)	24 (63%)	0 (0%)
	Genus	344	116 (34%)	27 (23%)	79 (23%)	1 (1%)
	Species	1,892	294 (16%)	176 (60%)	196 (10%)	56 (29%)

*Antarctic refers to waters south of the Polar Front (ca. 60°S).

Table 7

 7 Investigated families with mention of their environmental settings (from Mah and Blake 2012) their presence in the Southern Ocean (SO; from[START_REF] Moreau | Antarctic and sub-Antarctic Asteroidea database[END_REF]) and whether genetic sequences are available for the Southern Ocean. Ant: Antarctic (i.e. South of the Polar Front ~-60°; sub-Ant: sub-Antarctic (i.e. North of the Polar Front and south of the Subtropical Front ~-45°). * from Mah and Blake 2012; ** from[START_REF] Moreau | Antarctic and sub-Antarctic Asteroidea database[END_REF]

	Superorder	Order	Family	Present in cold or deep-sea waters*	Primarily or only present in cold waters*	Exclusively found in the deep sea *	Recorded in the SO**	Available sequences from the SO in this work
	NA	Velatida	Pterasteridae	YES	YES	NO	Ant & sub-Ant	YES
			Korethrasteridae	YES	YES	YES	Ant & sub-Ant	YES
	Forcipulatacea	Brisingida	Freyellidae	YES	YES	YES	Ant & sub-Ant	YES
			Brisingidae	YES	YES	YES	Ant & sub-Ant	YES
		Forcipulatida	Asteriidae	YES	NO	NO	Ant & sub-Ant	YES
			Heliasteridae	YES	NO	NO	Ant & sub-Ant	YES
			Pedicellasteridae	YES	YES	YES	Ant & sub-Ant	YES
			Stichasteridae	YES	NO	NO	Ant & sub-Ant	YES
			Zoroasteridae	YES	YES	YES	Ant & sub-Ant	NO
	Spinulosacea	Spinulosida	Echinasteridae	YES	NO	NO	Ant & sub-Ant	YES
	Valvatacea	Paxillosida	Astropectinidae	YES	YES	NO	Ant & sub-Ant	YES
			Ctenodiscidae	YES	YES	YES	Ant & sub-Ant	NO
			Luidiidae	YES	NO	NO	Doubtful (L.	NO
			Porcellanasteridae	YES	YES	YES	clathrata) Ant & sub-Ant	YES
			Pseudarchasteridae	YES	YES	NO	Ant & sub-Ant	YES
		Notomyotida	Benthopectinidae	YES	YES	YES	Ant & sub-Ant	YES
		Valvatida	Acanthasteridae	NO	NO	NO	NO	NO
			Archasteridae	NO	NO	NO	NO	NO
			Asterinidae	YES	NO	NO	Ant & sub-Ant	YES
			Asteropseidae	YES	NO	NO	NO	NO
			Ganeriidae	YES	YES	YES	Ant & sub-Ant	YES
			Goniasteridae	YES	YES	YES	Ant & sub-Ant	YES
			Leilasteridae	YES	YES	YES	Only known from	YES
							Shag Rocks
			Mithrodiidae	NO	NO	NO	NO	NO
			Odontasteridae	YES	YES	NO	Ant & sub-Ant	YES
			Oreasteridae	YES	NO	NO	NO	NO
			Poraniidae	YES	YES	NO	Ant & sub-Ant	YES
			Solasteridae	YES	YES	NO	Ant & sub-Ant	YES
	* from Mah & Blake 2012
	** from Moreau et al., 2018

Table 7

 7 Investigated families with mention of their environmental settings (from Mah and Blake 2012) their presence in the Southern Ocean (SO; from Moreau et al. 2018) and whether genetic sequences are available for the Southern Ocean. Ant: Antarctic (i.e. South of the Polar Front ~-60°; sub-Ant: sub-Antarctic (i.e. North of the Polar Front and south of the Subtropical Front ~-45°). * from Mah and Blake 2012; ** from Moreau et al. 2018.). Eleven of these 28 investigated families are exclusively found in the deep sea and 17 are primarily or only present in cold environments. Twenty families collected in the Southern Ocean are represented by at least one COI sequence and all but one (Leilasteridae) are found in both Antarctic and sub-Antarctic waters (Table 7 Investigated families with mention of their environmental settings (from Mah and Blake 2012) their presence in the Southern Ocean (SO; from Moreau et al. 2018) and whether genetic sequences are available for the Southern Ocean. Ant: Antarctic (i.e. South of the Polar Front ~-60°; sub-Ant: sub-Antarctic (i.e. North of the Polar Front and south of the Subtropical Front ~-45°). * from Mah and Blake 2012; ** from Moreau et al. 2018.).

Table 8

 8 Delineated Southern Ocean species in the six investigated clades, with a note regarding the need for a taxonomic revision. Counts based on available genetic sequences. SO: Southern Ocean. *Specimens from the Kerguelen Plateau also fall into the species Glabraster antarctica.

	Family	Genus (if	n of	n of species found in	n of species found in the	Needed
		found in the SO)	delineated species (ASAP)	the SO and number of endemic ones	Antarctic and number of endemic ones	systematic revision
	Ganeriidae	Cuenotaster	1	1 -1 (100%)	1 -1 (100%)	No
		Perknaster	9	9 -9 (100%)	9 -7 (78%)	Yes
		Cycethra	2	2 -2 (100%)	0 -0 (0%)	Yes
	Odontasteridae	Odontaster	8	7 -6 (75%)	7 -4 (50%)	Yes
		Diplodontias	2	1 -1 (50%)	0 -0 (0%)	No
		Acodontaster	7	7 -7 (100%)	7 -6 (86%)	Yes
	Benthopectinidae	Cheiraster	4	2 -1 (25%)	2 -1 (25%)	Yes
	Solasteridae	Solaster -	13	5 -5 (38%)	3 -2 (15%)	Yes
		Crossaster -
		Heterozonias
		Lophaster -	16	16 -15 (94%)	15 -13 (81%)	Yes
		Paralophaster
	Echinasteridae	Henricia	20	2 -2 (10%)	1 -1 (5%)	Yes
		Rhopiella	15	15 -15 (100%)	13 -13 (87%)	Yes
	Pterasteridae	Pteraster &	14	12 -6 (43%)	9 -5 (36%)	Yes
		Diplopteraster
		Hymenaster	13	12 -11 (85%)	12 -10 (77%)	Yes
	Poraniidae	Glabraster	NA	1 -1 (NA)	1 -0 (NA)	No
	(from Moore et al., 2018)	antarctica*
	Asteriidae	Diplasterias	NA	3 -3 (NA)	3 -1 (NA)	Yes
	(from Moreau et al., 2019)
		Lysasterias	NA	4 -4 (NA)	4 -4 (NA)	Yes
		Notasterias	NA	3 -3 (NA)	3 -3 (NA)	Yes
	Astropectinidae (From	Bathybiaster	NA	2 -1 (NA)	2 -1 (NA)	Yes
	Moreau et al., 2019)
		Psilaster	NA	4 -2 (NA)	4 -2 (NA)	Yes

  . Firstly, the presence of ubiquitous or bipolar clades in deep-sea taxa (e.g. in Pteraster spp; Lophaster furcilliger; Bathybiaster vexillifer; Bathybiaster loripes) reinforces the hypothesis of persistence in the deep sea with possible colonisation events of Antarctic shelf environments. In this framework, B. loripes could have diverged from its sister species B. vexillifer as the result of a polar emergence scenario while within B. vexillifer, signs of a more recent sub-Antarctic emergence scenario are detected. Secondly, in shallow waters, potential species exchanges are very likely between the Southern Ocean and other regions: South America and South Atlantic islands (e.g.

  came to similar conclusions in his Discovery Reports and continued analyses by indicating the close morphological similarity between Bathybiaster and Psilaster except for P. charcoti "the least Bathybiaster-like of any Psilaster"(Fischer 1940).[START_REF] Mortensen | Handbook of the Echinoderms of the British Isles[END_REF] also doubted whether

  . It is extremely important that both solutions are used in an integrative framework (DeSalle et al., 2005), for example through the development of knowledge bases, by compiling various types of data (e.g. photographs, identification keys, field guides, original descriptions, genetic sequences). In the Southern Ocean, major efforts were made under the umbrella of the Census of Antarctic Marine Life in 2005 and the International Polar Year in 2007-2009

• Bootstrap Spanning Values for each BSN

  Available online at https://onlinelibrary.wiley.com/doi/10.1002/ece3.5280• Statistical Parsimony networksStatistical Parsimony network indicating genetic relationships among sampling locations for each genera of interest. Major delineated clades are represented on maps attached to each haplotype network. Inter-specific distance between delineated entities using the K2P model are also presented for each genus.

	Species level	BSV	Genus level	BSV
	Bouv_Bal&Sco	0,9981	Ob&Lena_PEd&Mar	0,8639
	DS&WL_Bal&Sco	0,9332	PEd&Mar_Cro	0,9876
	Heard_Cro	0,9964	Cro_Heard	0,9409
	Ker_Heard Mac_Cro PBay_ALand PEd&Mar_Cro PEd&Mar_Ob&Lena QML&EL_PBay Ross_ALand Ross_Bal&Sco SG&Sha_AP&SSh SOrk_AP&SSh SOrk_SG&Sha SSand_SG&Sha TdF_Cro TdF_Fal TdF_SArg TdF_SChi TdF_SOrk WS_AP&SSh WS_Ross Bount&Ant_Cam&Auc Bouv_SSand DS&WL_Bouv DS&WL_QML&EL 0,8019 0,9944 0,6308 0,9997 1 0,9889 0,9337 1 0,9972 0,9999 1 0,9996 0,9818 0,9978 0,9998 0,9999 0,9991 0,9999 1 1 1 0,8505 0,9411 DS&WL_Bal&Sco 0,8993 Ross_DS&WL 0,9657 ALand_Ross 0,9994 WS_ALand 0,9922 PBay_ALand 0,9994 SOrk_PBay 0,9962 AP&SSh_SOrk 0,9982 SG&Sha_AP&SSh 0,9991 TdF_SG&Sha 0,985 Fal_SChi 0,8806 SArg_Fal 0,9836 TdF_SArg 0,9955 Heard_TdF 0,8572 PEd&Mar_Heard 0,9808 PEd&Mar_Ker 0,7486 Brooders BSV Cro_PEd&Mar 0,9906 • Metadata associated with barcode sequences Heard_Ker Ker_SG&Sha SSand&SG_Sha AP&SSh_SG&Sha AP&SSh_SOrk TdF_SOrk TdF_Fal Fal_SArg SArg_SChi SOrk_WS WS_Ross WS_PBay WS_ALand PBay_ALand PBay_Bal&Sco Bal&Sco_Bouv DS&WL_Bal&Sco ALand_QML&EL Cro_Mac Bount&Ant_Cam&Auc QML&EL_SArg Bouv_QML&EL AP&SSH_SG&Sha SOrk_AP&SSh SSand_Fal WS_SSand WS_ALand SOrk_WS Ross_SOrk Ross_Bouv PBay_DS&WL Bal&Sco_PBay Ross_Bal&Sco TdF_Ross Cro_TdF Heard_Cro Heard_PEd&Mar Ob&Lena_Heard Broadcasters Ker_Ob&Lena	0,9979 0,9227 0,8376 1 0,8828 0,6624 0,9998 0,9326 1 0,7573 0,767 0,9971 0,9687 0,9908 0,9998 0,9998 1 0,99350126 1 0,9937 1 0,9805 0,8269 0,9961 0,9993 0,9771 1 0,9722 0,9912 0,9899 0,9883 0,9816 0,9998 0,9998 0,9988 0,9917 0,987 0,7099 BSV 0,9993
	SSand_Ob&Lena	0,9147	SArg_AS&BS	0,765
	Cam&Auc_Bal&Sco 0,8568	SChi_AS&BS	0,9467
			Mac_AS&BS	0,8733
			Bount&Ant_Cam&Auc	0,9609

General discussion

Available online at https://onlinelibrary.wiley.com/doi/full/10.1111/jbi.12965

References

ACKNOWLEDGEMENTS

The work was supported by a "Fonds pour la formation à la Recherche dans l'Industrie et dans l'Agriculture" (FRIA) grants to C. Moreau. This is contribution no.8 to the vERSO project (www.versoproject.be), funded by the Belgian Science Policy Office (BELSPO, contract n°BR/132/A1/vERSO).

ACKNOWLEDGEMENTS

This work was supported by a "Fonds pour la formation à la Recherche dans l'Industrie et l'Agriculture" (FRIA) grants to C. Moreau. C. Mah was funded by MNHN invited researcher grants (2013, 2014, 2015, 2016). This is contribution no. 16 to the vERSO project (www.versoproject.be), funded by the Belgian Science Policy Office (BELSPO, contract n°BR/132/A1/vERSO). This is contribution to the IPEV programs n°1124 REVOLTA and n°1044 PROTEKER and to team SAMBA of the Biogeosciences laboratory. We are grateful to the crew and participants of all the cruises and research programs involved in the capture of the samples included in this dataset: POKER 2, REVOLTA 1 & 2, CEAMARC, JR144, JR179, JR230, JR262, JR275, JR287, JR15005. We also thank the following institutions: California Academy of Sciences, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Shallow Marine Surveys Group, University of Lodz, Muséum national d'Histoire naturelle and University of Genoa, NIWA (National Institute of Water and Atmospheric Research) Invertebrate Collection.

ACKNOWLEDGEMENTS

The authors thank Dr. Gilles Escarguel (Lyon) for his help with the BSN procedure as well as Rachel Downey and Dr. David Barnes for helpful comments on an early manuscript. Marc

Data availability

All occurrences data are published and openly available through an Integrated Publishing Toolkit ensuring a free access to biodiversity data. All barcode genetic sequences are now freely available via the Barcode of Life Data System. These sequences are linked to photographs, identifications and metadata regarding their sampling.

E-mail: mr.moreau.camille@gmail.com Citation: Moreau, C., Agüera, A., Jossart, Q., & Danis, B. (2015). Southern Ocean Asteroidea: a proposed update for the Register of Antarctic Marine Species. Biodiversity data journal, (3), e7062, doi: 10.3897/BDJ.3.e7062.

ABSTRACT Background

The Register of Antarctic Marine Species (RAMS, De Broyer et al. 2015) is the regional component of the World Register of Marine Species (WoRMS Editorial Board 2015) in the Southern Ocean. It has been operating for the last ten years, with a special effort devoted towards its completion after the International Polar Year (IPY) in [2007][2008], in the framework of the Census of Antarctic Marine Life (CAML, 2005(CAML, -2010)). Its objective is to offer free and open access to a complete register of all known species living in the Southern Ocean, building a workbench of the present taxonomic knowledge for that region. The Antarctic zone defined by this dynamic and community-based tool has been investigated with a particular interest.

The Sub-Antarctic zone was a secondary objective during the establishment of the RAMS and is still lacking the impulse of the scientific community for some taxa.

New information

In the present study, more than 13,000 occurrences records of Asteroidea (Echinodermata)

have been compiled within the RAMS area of interest and checked against the RAMS species list of sea stars, using WoRMS Taxon Match tool. Few mismatches (basionym mistakes: i.e.

original name misspelled or incorrect) were found within the existing list and 97 unregistered species are actually occurring within the RAMS boundaries. After this update, the number of Asteroidea species was increased by around 50%, now reaching 295 accepted species.

ABSTRACT

The present dataset is a compilation of georeferenced occurrences of asteroids (Echinodermata: Asteroidea) in the Southern Ocean. Occurrence data south of 45°S latitude were mined from various sources together with information regarding the taxonomy, the sampling source and sampling sites when available. Records from 1872 to 2016 were thoroughly checked to ensure the quality of a dataset that reaches a total of 13,840 occurrences from 4,580 unique sampling events. Astrostole, Bathybiaster, Belgicella, Benthopecten, Brisinga, Brisingenes, Caimanaster, Calyptraster, Ceramaster, Cheiraster, Chitonaster, Chondraster, Cladaster, Clavaporania, Coscinasterias, Cosmasterias, Crossaster, Cryptasterias, Ctenodiscus, Cuenotaster, Cycethra, Diplasterias, Diplodontias, Diplopteraster, Dipsacaster, Dytaster, Echinaster, Eratosaster, Eremicaster, Freyastera, Freyella, Freyellaster, Fromia, Ganeria, Gaussaster, Gilbertaster, Glabraster, Granaster, Henricia, Hippasteria, Hymenaster, Hymenodiscus, Hyphalaster, Kampylaster, Kenrickaster, Labidiaster, Leptychaster, Lethasterias, Lithosoma, Lonchotaster, Lophaster, Luidia, Lysasterias, Macroptychaster, Mediaster, Meridiastra, Mimastrella, Mirastrella, Myxoderma, Neosmilaster, Notasterias, Notioceramus, Novodinia, Odinella, Odontaster, Odontohenricia, Ophidiaster, Paralophaster, Paranepanthia, Patiriella, Paulasterias, Pectinaster, Pedicellaster, Pentagonaster, Pergamaster, Peribolaster, Perissasterias, Perknaster, Persephonaster, Pillsburiaster, Plutonaster, Poraniopsis, Porcellanaster, Proserpinaster, Psalidaster, Pseudarchaster, Pseudechinaster, Psilaster, Pteraster, Radiaster, Remaster, Rhopiella, Saliasterias, Sclerasterias, Scotiaster, Smilasterias, Solaster, Sphaeriodiscus, Stichaster, Styracaster, Taranuiaster, Tarsaster, Tremaster, Vemaster, Zoroaster.

Chapter 1

Reproductive strategy as a piece of the biogeographic puzzle: a case study using Antarctic sea stars (Echinodermata, Asteroidea)

Eléaume, Christopher Mah, Vladimir Laptikhovsky and Anna Jażdżewska for their data and identification contributions. Prof. Richard Ladle for the help he offered in the last steps of the submission process. The work was supported by a "Fonds pour la formation à la Recherche dans l'Industrie et l'Agriculture" (FRIA) grants to C. Moreau. This is contribution no. 13 to the vERSO project (www.versoproject.be), funded by the Belgian Science Police Office (BELSPO, contract n°BR/132/A1/vERSO) and a contribution to team BioME of the Biogéosciences laboratory.

SUPPORTING INFORMATION

Appendix 1

• Data source and quality control for Southern Ocean Asteroidea

• Bootstrap Spanning Values for each Bootstrap Spanning Network Chapter 2

Is reproductive strategy a key factor in understanding the evolutionary history of Southern Ocean Asteroidea (Echinodermata)?

ABSTRACT Life traits such as reproductive strategy can be determining factors of species evolutionary history and explain the resulting diversity patterns. This can be investigated using phylogeographic analyses of genetic units. In this work, the genetic structure of five asteroid genera with contrasting reproductive strategies (brooding: Diplasterias, Notasterias and Lysasterias versus broadcasting: Psilaster and Bathybiaster) was investigated in the Southern Ocean. Over 1,400 mtDNA cytochrome C oxidase subunit I (COI) sequences were analysed using five species delineation methods (ABGD, ASAP, mPTP, sGMYC and mGMYC), two phylogenetic reconstructions (ML and BA), and molecular clock calibrations, in order to examine the weight of reproductive strategy in the observed differences among phylogeographic patterns. We hypothesised that brooding species would show higher levels of genetic diversity and species richness along with a clearer geographic structuring than broadcasting species. In contrast, genetic diversity and species richness were not found to be significantly different between brooders and broadcasters, but broadcasters are less spatially structured than brooders supporting our initial hypothesis and suggesting more complex

RESULTS

In total, 1,416 sequences of 612bp were included in the analyses (Appendix 2; Table 4; Figure 27), varying from 224 for Lysasterias to 318 for Notasterias. No stop codons nor significant evidence for base heterogeneity were observed.

Species delineation

Species delineation applied to all genera show contrasting results dependent upon the method applied (Figure 28; Figure 29; Figure 30; Table 5). Overall, the mGMYC method delineated the highest number of entities (79), while mPTP was the most conservative (19).

Following a conservative approach, we based our work on the following delineated entities: two for Bathybiaster, three for Diplasterias and Notasterias and four for P. charcoti and

Lysasterias. These results are in line with haplotype networks and phylogenetic groupings (Figure 28; Figure 29; Figure 30; Appendix 2). Among the brooding entities, only one matches with an identified morphological species: Diplasterias meridionalis. In broadcasters, one delineated entity of the genus Bathybiaster comprises specimens from the Arctic identified as

Bathybiaster vexillifer and Psilaster andromeda.

Genetic diversity of the delineated entities ranged from 0.00160 (P. charcoti -clade 3) to 0.01547 (Diplasterias sp2) for nucleotide diversity and from 0.394 (P. charcoti -clade 3) to 0.924 (P. charcoti -clade 1) for haplotype diversity (Table 4). The number of segregating sites varied from 11 (D. meridionalis) to 50 (P. charcoti -clade 1). Mean intraspecific distances varied from 0.16% (P. charcoti -clade 3) to 1.6% for Diplasterias sp2 ( Chapter 3

Is reproductive strategy a key factor in understanding the evolutionary history of Southern Ocean Asteroidea (Echinodermata)?

Chapter 3

The overlooked diversity of Southern Ocean sea stars (Asteroidea) reveals original evolutionary pathways.

ABSTRACT

Benthic life in the Southern Ocean features unique life history traits and species assemblages, but the origin and evolution of many of these taxonomical groups is still unclear. Exploring macro-ecological sea star (Asteroidea) diversity patterns through a comprehensive phylogeny based on over 4,400 barcode sequences, we illustrate that the richness of Southern Ocean asteroids has generally been overlooked and misinterpreted. We also demonstrate that the current Southern Ocean sea star diversity mainly emerged from recent diversification. A central evolutionary scenario could explain these signatures through successive invasion and exchange events between the Southern Ocean and adjacent regions with comparable environmental conditions, during periods of rapid environmental change. Finally, we emphasise the importance of employing and endorsing the use of extensive genetic barcode libraries for future biodiversity studies.

Keywords

Antarctica -COI mtDNA -Biodiversity -Echinodermata -Evolution -Phylogeography

Sea stars have been used as case studies in numerous biological studies (see in [START_REF] Lawrence | Starfish: biology and ecology of the Asteroidea[END_REF], which have revealed key functions and significant ecological roles performed by many species in marine ecosystems [START_REF] Paine | Food web complexity and species diversity[END_REF][START_REF] Mcclintock | Trophic biology of Antarctic shallow-water echinoderms. Marine ecology progress series[END_REF][START_REF] Pratchett | planci L.), and their effects on coral reef ecosystems[END_REF]McClintock et al., 2008). The Southern Ocean is no exception, harbouring a singular marine fauna (David & Saucède, 2015), and with sea stars influencing ecosystems in terms of diversity, abundance and ecological roles [START_REF] Mcclintock | A review of the chemical ecology of Antarctic marine invertebrates[END_REF]McClintock et al., 2008;[START_REF] Clarke | Antarctic marine benthic diversity: patterns and processes[END_REF].

Contemporary sea stars all belong to the monophyletic sub-class Neoasteroidea [START_REF] Blake | A classification and phylogeny of post-Palaeozoic sea stars (Asteroidea: Echinodermata)[END_REF][START_REF] Gale | Phylogeny and classification of the Asteroidea (Echinodermata)[END_REF] that diversified after their near complete extinction at the Permian-Triassic boundary (ca. 250 Mya; [START_REF] Chen | End-Permian extinction and subsequent recovery of the Ophiuroidea (Echinodermata)[END_REF][START_REF] Twitchett | Early Triassic recovery of echinoderms[END_REF]. Today, it is the second most diverse class of echinoderms after the Ophiuroidea (~2,100 species), with around 1,900 described species worldwide (WoRMS, 2019). The global diversity of sea stars is believed to be considerably underestimated due to various taxonomic issues and sampling biases [START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF][START_REF] Moreau | Is reproductive strategy a key factor in understanding the evolutionary history of Southern Ocean Asteroidea (Echinodermata)?[END_REF]. In the global ocean, sea star diversity patterns reveal high levels of species richness in tropical regions (e.g. [START_REF] Blake | Adaptive zones of the class Asteroidea (Echinodermata)[END_REF] and a latitudinal diversity gradient decreasing towards the poles, with lower richness levels recorded in the Arctic compared to the Antarctic [START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF]. Despite this decreasing species richness gradient towards the poles, the cold polar oceans harbour unusual levels of richness in sea star families [START_REF] Mah | Global diversity and phylogeny of the Asteroidea (Echinodermata)[END_REF].

All seven orders of the class Asteroidea and 75% of known extant families are found in the Southern Ocean [START_REF] Moreau | Southern Ocean Asteroidea: a proposed update for the Register of Antarctic Marine Species[END_REF]2018). Such a wide taxonomic richness among an entire class is not typical in the Southern Ocean, where long-term biogeographic isolation and extreme environmental conditions have conditioned the specialisation of taxa, especially at high taxonomic levels (i.e. family). For instance, the Southern Ocean ichthyofauna (fish) has been described as "a taxonomically restricted and endemic modern fauna" [START_REF] Eastman | The nature of the diversity of Antarctic fishes[END_REF], and only a fifth of crinoid families are present in the Southern Ocean [START_REF] Eléaume | Southern Ocean crinoids. Biogeographic atlas of the Southern Ocean[END_REF].

The wide taxonomic richness of Southern Ocean sea stars, however, does not preclude their singularity, with 59% of endemic species recorded south of the Subtropical Front and 29% of them south of the Polar Front [START_REF] Moreau | Reproductive strategy as a piece of the biogeographic puzzle: a case study using Antarctic sea stars (Echinodermata, Asteroidea)[END_REF].

Under-sampled marine environments of the Southern Ocean have been subject to renewed biodiversity research efforts since the International Polar Year (IPY 2007(IPY -2009) ) and

Genetic data compilation

DNA barcoding is an effective tool for specimen identification in echinoderms [START_REF] Ward | DNA barcoding discriminates echinoderm species[END_REF][START_REF] Layton | Exploring Canadian echinoderm diversity through DNA barcodes[END_REF] and an asset for resolving the phylogeny at low taxonomical levels, particularly by integrating a large number of specimens [START_REF] Hajibabaei | DNA barcoding: how it complements taxonomy, molecular phylogenetics and population genetics[END_REF]. DNA sequences of a fragment of the mitochondrial gene cytochrome c subunit I (COI) were compiled from two sources. First, all publicly available sequences from the Barcode of Life Data System (BOLD, [START_REF] Ratnasingham | BOLD: The Barcode of Life Data System[END_REF], including the ones previously mined through GenBank [START_REF] Sayers | [END_REF], for the class Asteroidea were downloaded and compiled without limitations regarding sample location. In addition, new sequences were obtained in our laboratories. Extraction methods were either based on a salting-out protocol (modified from [START_REF] Sunnucks | Numerous transposed sequences of mitochondrial cytochrome oxidase I-II in aphids of the genus Sitobion (Hemiptera: Aphididae)[END_REF]following Moreau et al., 2019) or the QIAGEN DNA Blood and Tissue kit. Amplifications were completed using the echinoderm forward primer LCOech1aF1 and the universal HCO2198 reverse primer [START_REF] Folmer | DNA primers for amplification of mitochondrial cytochrome c oxidase subunit I from diverse metazoan invertebrates[END_REF]. Sequence

editing and alignment were performed in CodonCode Aligner v6.0.2. All sequences were then translated using the echinoderm mitochondrial genetic code to ensure the absence of stop codons. Sequences were aligned using the MUSCLE alignment process [START_REF] Edgar | MUSCLE: multiple sequence alignment with high accuracy and high throughput[END_REF]. To maximise species coverage and fragment overlap, we defined a minimum length cut-off of 600 bp.

Tree reconstruction

Sequences were used for the reconstruction of a global phylogenetic tree based on Bayesian Inference and using unique haplotypes. The PartitionFinder v2 software [START_REF] Lanfear | PartitionFinder 2: new methods for selecting partitioned models of evolution for molecular and morphological phylogenetic analyses[END_REF] was used on the CIPRES Science Gateway [START_REF] Miller | Creating the CIPRES Science Gateway for inference of large phylogenetic trees[END_REF] to select the best-fit model of evolution using a Bayesian information criterion (result: GTR+I+G). The phylogeny was inferred using an XML file created with BEAUti v1.8.4 [START_REF] Drummond | Bayesian phylogenetics with BEAUti and the BEAST 1.7[END_REF], a strict clock model with a lognormal prior for "clock.rate" such that the median reflected a universal divergence time of echinoderm COI of 3.1 to 3.5% per Myr (McCartney et al., 2000), a MCMC chain of 10 x 106 generations sampling every 1,000 trees and a Yule process speciation prior.

The XML file was used with the software BEAST v1.8.4 on the CIPRES Science Gateway to reconstruct a time-calibrated tree. TreeAnnotator v1.8.4 calculated a consensus tree that was visualised using FigTree v1.4.3 (http://tree.bio.ed.ac.uk/software/figtree/).

From data mining to archiving

All the data collected, obtained through lab work and used in the framework of this thesis have been deposited into several online, open-source data repositories.

Data collection

All occurrence data were acquired from various sources: specialised information system (OBIS, GBIF, ANTABIF), legacy literature and old cruise reports (Biodiversity Heritage Library), data papers (e.g. Zookeys, Biodiversity Data Journal), collaborations within the scientific community and additions of newly identified specimens. All barcode genetic sequences obtained for this thesis either through lab work or from previous private or public datasets available in the Barcode of Life Data System.

Data treatment

All occurrences were checked individually to ensure quality standards such as: the absence of replicates, a correct georeferencing, an up-to-date nomenclature (using the taxon-match tool implemented in WoRMS). Each occurrence was then associated with a depth (GEBCO) and a bioregion based on their geographic coordinates. Electropherograms of each genetic sequence were inspected when available to ensure the quality of the consensus sequences. The absence of stop codon was also ensured Appendices Appendix 1

• Moreau, C., Saucède, T., Jossart, Q., Agüera, A., Brayard, A., & Danis, B. (2017). Reproductive strategy as a piece of the biogeographic puzzle: a case study using Antarctic sea stars (Echinodermata, Asteroidea). Journal of Biogeography, 44(4), 848-860.

→ Chapter 1

Appendix 2