Alex Baumel

Yves Vigouroux

Peter Linder

Hélène Ralimanana

Jacqueline Razanatsoa

Cédrique

First of all, Guillaume Besnard was a great supervisor, always available for feedback, with this intuition for the curious details, and we spent hours in the afternoon heat of Madagascar sterilising grass leaves. Maria Vorontsova was involved in all parts of this dissertation. Pilar Catalán gave me the opportunity to participate in her and Miguel Minaya's work on Loliinae

Introduction

Patterns and processes in biogeography

The spatial distribution of species Understanding the distribution of organisms on Earth has been a long-standing goal of biology. Why are some regions more diverse than others? Why are some species endemic and others widespread? How have groups with a common ancestor come to colonise widely separated ranges? Questions such as these form the core of the discipline of biogeography [START_REF] Cox | Biogeography: an ecological and evolutionary approach[END_REF]. Studying the geography of earth's biodiversity is an challenging area of fundamental research but has implications that go beyond pure scientific interest. Organisms interact with their physical environment and each other, forming dynamic ecosystems (Tansley 1935) which not least are the basis of human civilisation. In an epoch where humans are modifying the biosphere in unprecedented ways, both through physical alteration and the rearrangement of biotic communities [START_REF] Waters | The Anthropocene is functionally and stratigraphically distinct from the Holocene[END_REF], it is urgent to understand the fundamental processes behind the spatial distribution of biodiversity.

Biodiversity can be studied at various spatial and temporal scales, from biomes to genes, and from geological epochs to days, and these levels all have their own dynamics and influence each other [START_REF] Levin | The problem of pattern and scale in ecology: the Robert H. MacArthur award lecture[END_REF]). One of the most commonly studied units, both in evolutionary biology and ecology, is the species. The existence of species appears an evident fact to most, but defining and delimiting species has been a major challenge in biology. Today, most biologists explicitly or implicitly share a species concept rooted in the theory of evolution, although they may be divided on how to detect and tell apart species in practice [START_REF] Hey | On the failure of modern species concepts[END_REF][START_REF] De Queiroz | Species concepts and species delimitation[END_REF]. A species is seen as an evolutionary independent lineage of organisms that has split from another lineage, a "separately evolving metapopulation lineage" [START_REF] De Queiroz | Species concepts and species delimitation[END_REF]. This is the concept I also apply in this dissertation.

The distribution of species on the planet is highly uneven, but some generalities do exist. For example, most species in a given locality are rare [START_REF] Preston | The commonness, and rarity, of species[END_REF], the number of species increases with area in a repeatable manner [START_REF] Mcguinness | Species-area curves[END_REF], and, on a global scale, the tropics have more species than higher latitudes in most groups of organisms [START_REF] Hillebrand | On the generality of the latitudinal diversity gradient[END_REF]). However, beneath these general observations, there is a diversity of patterns more complicated: the taxonomic composition of species assemblages differs between continents, creating distinct biogeographic regions recognised since more than a century (Sclater 1858, Engler 1879). Physically similar biomes, such as tropical forests, savannahs or high mountains, can be found on different continents, but the species, the biota, that compose them differ [START_REF] Nelson | From Candolle to Croizat: comments on the history of biogeography[END_REF]. Biogeography has traditionally addressed these patterns from two angles: an ecological one, focusing on the current-day, observable mechanisms that shape distribution patterns, and a historical-evolutionary one, studying the impact of past geological events and evolutionary history [START_REF] Cox | Biogeography: an ecological and evolutionary approach[END_REF]). These two have long existed as two parallel disciplines, with little exchange, but there have been increasing efforts to merge them [START_REF] Wiens | Historical biogeography, ecology and species richness[END_REF], Ricklefs & Jenkins 2011).

Ecological processes

Thinking in ecology has been strongly influenced by the idea that an organism is adapted to a particular set of environmental factors and other organisms it interacts with, which together form its niche [START_REF] Grinnell | The niche-relationships of the California thrasher[END_REF][START_REF] Elton | Animal ecology[END_REF][START_REF] Hutchinson | Concluding remarks[END_REF]. Thus, the niche of an organism would determine where it occurs, and the environment would "filter" species adapted to it [START_REF] Weiher | Advances, challenges and a developing synthesis of ecological community assembly theory[END_REF]. This is evident in many cases, with e.g. plant species having adaptations to cold, arid, or humid climates, and being unable to survive under opposing conditions. Species interact with each other, and in a given location, different organisms with exactly the same niches are theoretically expected to exclude each other [START_REF] Hardin | The competitive exclusion principle[END_REF]. Organisms may however co-exist when they have slightly different requirements and thus partition the niche space [START_REF] Macarthur | The limiting similarity, convergence, and divergence of coexisting species[END_REF]. That different organisms co-exist despite competing for the same resources is evident for example in plant communities, where individuals directly compete for space and light.

The example of individuals in a plant community was also used to formalise an alternative explanation of species co-existence: individuals of different species may be ecologically equivalent (i.e. their niches overlap completely) but can co-exist in a dynamic equilibrium, where random ecological drift constantly opens vacant spaces that are filled by local or newly arriving species [START_REF] Hubbell | The unified neutral theory of biodiversity and biogeography[END_REF]). Hubbell's neutral theory highlights the role of new individuals arriving in a community from a regional source, and builds up on other theories that emphasise the movement of individuals and species, notably the theory of island biogeography [START_REF] Macarthur | The theory of island biogeography[END_REF]. These theories underline that species assemblages are dynamic and change over time. Linked to this is the growing appreciation that local communities of species are not closed, but part of and exchanging with a regional "pool" of species [START_REF] Ricklefs | Community diversity: relative roles of local and regional processes[END_REF](Ricklefs , 2004). This regional pool is built up through evolutionary processes, i.e. the origin and disappearance of species. Historical contingency will thus influence both regional and local assemblages (Ricklefs 2004).

Evolutionary processes

Organismal lineages are linked through common ancestry. They emerge through speciation in a given area, can move to another area, and will eventually go extinct. These three processes, speciation, dispersal and extinction, thus fundamentally underlie species diversity and distribution [START_REF] Wiens | The causes of species richness patterns across space, time, and clades and the role of "ecological limits[END_REF]. For example, differences in species richness between two regions can be explained by a higher speciation rate, or lower extinction rate, in one of them [START_REF] Wiens | The causes of species richness patterns across space, time, and clades and the role of "ecological limits[END_REF]. High endemism in an area, or in a group of organisms, can be due to restricted dispersal and in situ speciation, for example on islands [START_REF] Losos | Adaptation and diversification on islands[END_REF]. One pattern that has received particular attention from evolutionary biogeographers is that of disjunct distributions [START_REF] Cox | Biogeography: an ecological and evolutionary approach[END_REF]): how has an organism, or a group of organisms, come to be present in widely separated areas?

Early biogeographers, influenced by Darwin and Wallace's recent theory of evolution, attempted to explain disjunct distributions with the area-of-origin concept: lineages would have originated in one area, and reached their current distributions through dispersal [START_REF] Nelson | From Candolle to Croizat: comments on the history of biogeography[END_REF]. A later arising, opposing view was that of panbiogeography, which explained disjunctions through vicariance, the separation of ancient widespread populations (defended mainly by Léon Croizat, e.g. [START_REF] Croizat | Panbiogeography; or, An introductory synthesis of zoogeography, phytogeography, and geology, with notes on evolution, systematics, ecology, anthropology, etc[END_REF]). The acceptance of plate tectonics in geology appeared to shift support towards this latter idea, providing a mechanism that could explain ancient continental connections [START_REF] Cox | Biogeography: an ecological and evolutionary approach[END_REF]). In the southern hemisphere, it was shown that the now widely separated continents were once joined in one supercontinent, Gondwana, from the Carboniferous until roughly the Cretaceous, around 150 Ma (million years ago); this could explain e.g. similarities of fossil floras from South America, Antarctica, Africa, Australia, and India [START_REF] Mcloughlin | The breakup history of Gondwana and its impact on pre-Cenozoic floristic provincialism[END_REF]. Biotas of continental islands, such as Madagascar or New Zealand, were explained as being predominantly remnants of an ancient Gondwanan fauna and flora that have since evolved in isolation [START_REF]Composition, origin, and affinities of the Madagascan vascular flora[END_REF][START_REF] Craw | New Zealand biogeography: a panbiogeographic approach[END_REF].

With the arrival of molecular phylogenetics and especially divergence time estimation (see next section), it became however increasingly clear that many lineages must have reached their current range through dispersal: many lineage divergences were much younger than the presumed vicariance event [START_REF] De Queiroz | The resurrection of oceanic dispersal in historical biogeography[END_REF][START_REF] Renner | Relaxed molecular clocks for dating historical plant dispersal events[END_REF]). In the southern hemisphere, dispersal between formerly connected Gondwanan landmasses was found to have been more frequent than expected, especially in plants [START_REF] Sanmartín | Southern hemisphere biogeography inferred by event-based models: plant versus animal patterns[END_REF]. The biotas of islands like Madagascar and New Zealand are now seen as largely dispersal-assembled [START_REF] Winkworth | Plant dispersal N.E.W.S from New Zealand[END_REF], Yoder & Nowak 2006, Buerki et al. 2013). Even for groups with a well-established Gondwanan fossil record, such as the southern beeches (Nothofagus), it was suggested that some recent dispersal must have taken place [START_REF] Cook | Not so ancient: the extant crown group of Nothofagus represents a post-Gondwanan radiation[END_REF]. Some inferred dispersal events covered extremely large distances, such as that of cold-adapted crowberries (Empetrum) from the Arctic to the Antarctic [START_REF] Popp | A single Mid-Pleistocene long-distance dispersal by a bird can explain the extreme bipolar disjunction in crowberries (Empetrum)[END_REF].

It is important to distinguish how the term "dispersal" is applied in ecology and biogeography (Ricklefs & Jenkins 2011). In the ecological sense, dispersal describes the movement of individuals between habitat patches and populations [START_REF] Matthysen | Multicausality of dispersal: a review. Dispersal ecology and evolution[END_REF]). In the evolutionary-biogeographical sense, which I apply in this section and the remainder of this dissertation, dispersal describes the macroevolutionary event of a lineage moving to a new area of distribution, with or without simultaneous speciation [START_REF] Cox | Biogeography: an ecological and evolutionary approach[END_REF]. Biogeographers usually, and implicitly, include both the actual dispersal event as well as successful establishment ("effective dispersal", Nathan et al. 2003), without which there would be no lasting evolutionary imprint in the form of a new range or new lineage. Lineage dispersal was long seen as a rare, unlikely and elusive process, conveniently invoked when other explanations failed (e.g. [START_REF] Nelson | From Candolle to Croizat: comments on the history of biogeography[END_REF]. Indeed, for plants it has been suggested that specific adaptations for long-distance dispersal may not exist, and that such dispersal events are often the result of rare drift through extreme climatic events [START_REF] Nathan | Long-distance dispersal of plants[END_REF]. Nevertheless, lineage dispersal may have predictable components. This includes the directionality of dispersal vectors, e.g. ocean currents, prevailing winds, or bird migration routes (Gillespie et al. 2012). Also, dispersal probability is expected to decrease in a predictable manner with distance, although it was suggested to be higher at very long distances than expected under an exponential decrease (Nathan et al. 2003).

Lineage dispersal is moreover not independent from local environmental factors. For plants, it has been shown that ecological niches, and the biomes they occur in, are relatively conserved in evolutionary history [START_REF] Prinzing | The niche of higher plants: evidence for phylogenetic conservatism[END_REF][START_REF] Crisp | Phylogenetic biome conservatism on a global scale[END_REF]. This means that lineages will usually be confined to the conditions they evolved in, and a given area will preferentially be colonised by pre-adapted species (Donoghue 2008). However, there are examples where traits evolved multiple times in independent groups and facilitated adaptation, for example fire resistance in savannah trees (Simon et al. 2009, Maurin et al. 2014) or C4 photosynthesis in grasses and other plants (see section 1.3). In the south-temperate danthonioid grasses, it was shown that climatic niches, i.e. cold tolerance, evolved among clades, specifically following dispersal events (Humphreys & Linder 2013[START_REF] Wüest | Available climate regimes drive niche diversification during range expansion[END_REF]. Then again, an opinion paper suggested that the evolvability of traits is itself often conditioned by a clade's evolutionary and biogeographic history [START_REF] Edwards | Is it easy to move and easy to evolve? Evolutionary accessibility and adaptation[END_REF]. The authors concluded that the ease of dispersal versus niche evolution must be studied considering the context of each particular group. Accordingly, an extensive survey of a relatively young tropical mountain has found recently that both adaptive shifts of lowland lineages as well as longdistance immigration of pre-adapted mountain lineages contributed to its biota [START_REF] Merckx | Evolution of endemism on a young tropical mountain[END_REF].

Molecular and analytical approaches to biogeography

Molecular phylogenetics

Phylogenetics, as the study of the relationships between organisms, derives directly from the theory of evolution [START_REF] Delsuc | Phylogenomics and the reconstruction of the tree of life[END_REF]. It uses the state of characters inherited from a common ancestor -homologous characters -to make hypotheses about branching order and evolutionary distance. Due to its large amount of characters, DNA is particularly useful for this [START_REF] Delsuc | Phylogenomics and the reconstruction of the tree of life[END_REF]. Typically, selected portions of genomes -e.g. particular genes or intergenic regions -are used to detect, through an alignment, homologous sites that differ and thus indicate an evolutionary change, i.e. a mutation (Anisimova et al. 2013). For a few years already, larger portions or even whole genomes have been used, marking the transition towards phylogenomics [START_REF] Delsuc | Phylogenomics and the reconstruction of the tree of life[END_REF]. This has been facilitated by the development of next-generation sequencing methods, which allow generating large amounts of sequences in parallel for a single sample [START_REF] Metzker | Sequencing technologies -the next generation[END_REF]). In plants for example, whole chloroplast genomes are assembled with relative ease even from short sequence reads due to their conserved structure and high copy number, and have increasingly been used to resolve relationships (Tonti-Filippini et al. 2017).

The possibility of using different parts of the genome also allows to detect reticulate patterns of evolution that are not captured in a bifurcating species tree. While organellar DNA such as that of chloroplasts is usually transmitted maternally [START_REF] Greiner | Why are most organelle genomes transmitted maternally?[END_REF] and thus reflects seed dispersal in plants, nuclear DNA, transmitted by both parents, may reflect additional paths of dispersal (i.e. through pollen). Also, nuclear DNA is often subject to horizontal transfer, for example through hybridisation [START_REF] Kidwell | Lateral transfer in natural populations of eukaryotes[END_REF]. The combination of nuclear and chloroplast DNA has revealed intricate biogeographic patterns where new species arose from nuclear and chloroplast lineages of distant origins (e.g. in the grass subfamily Danthonioideae, Pirie et al. 2009). Also, duplication of genes or whole genomes has often generated families of paralogous genes, particularly in plants (Adams & Wendel 2005). Study of such gene families has allowed for example to demonstrate independent origins of C4 photosynthesis (e.g. Christin & Besnard 2009) or the evolution of cold tolerance in pooid grasses (Sandve et al. 2008).

Early methods for inferring phylogenetic relationships were based on distance measures or a parsimony method minimising the number of inferred changes [START_REF] Felsenstein | Inferring phylogenies[END_REF]). Today, probabilistic approaches that model substitution rates and site heterogeneity in a Maximum Likelihood or Bayesian framework are the methods of choice (Anisimova et al. 2013). The size of modern datasets combined with the complexity of phylogenetic calculations mean that analytical solutions -i.e. finding the best among all possible trees -are usually not feasible, and heuristics are used to search the space of trees [START_REF] Felsenstein | Inferring phylogenies[END_REF]). Probabilistic models have also allowed to integrate divergence time estimation into phylogenetics, which involves two main considerations: First, divergences have to be calibrated to absolute time by known ages (reviewed by [START_REF] Ho | Accounting for calibration uncertainty in phylogenetic estimation of evolutionary divergence times[END_REF]. These are most often fossils, which usually provide a minimum age for a given group. An exception is e.g. the appearance of pollen typical of flowering plants in the Early Cretaceous, which is assumed to provide a reasonable upper limit for their origin (Anderson et al. 2005). Early methods allowed setting a calibration point mainly as fixed age or hard lower or upper bound. More advanced methods allow specifying a parametric distribution, e.g. a normal distribution around a mean, or exponential or lognormal distributions which place most weight near the calibration age but have no hard bounds. Apart from the age uncertainty, the confidence with which one can attribute a fossil to a particular node of the phylogeny will also influence the analysis [START_REF] Ho | Accounting for calibration uncertainty in phylogenetic estimation of evolutionary divergence times[END_REF]. The second important part is the model of rate variation applied: in contrast with early assumptions of a fixed global "molecular clock", the rate of DNA sequence evolution varies more or less strongly between lineages [START_REF] Bromham | The modern molecular clock[END_REF]. This is usually accounted for with "relaxed" molecular clocks, which allow rates to be correlated between lineages (Thorne et al. 1998), to belong to discrete classes of a specified distribution (Drummond et al. 2006), or to form clusters of randomly distributed "local clocks" [START_REF] Drummond | Bayesian random local clocks, or one rate to rule them all[END_REF].

Analysis of range evolution

The phylogenetic relationships and divergence times inferred for a set of species, combined with their current distribution ranges, can be used to make hypotheses about the evolution of their distribution through time. The earliest such approaches built on the theory of plate tectonics and attempted to fit the sequence of species divergence to a sequence of area divergence in so-called taxon-area cladograms (reviewed in [START_REF] Cox | Biogeography: an ecological and evolutionary approach[END_REF]. Later techniques specifically attempted to infer events that led to changes in distribution, notably vicariance or dispersal (e.g. the influential dispersal-viariance analysis, DIVA, Ronquist 1997). Both kinds of approach applied a parsimony reasoning, attempting to infer the simplest history with the least necessary changes. Often, dispersal had to be invoked to explain disjunctions, but it was seen as random "noise" rather than an interesting process. Dispersal, like extinction, posed the problem of not being tractable from ancestor to descendant; both processes were thus minimised by applying penalties [START_REF] Cox | Biogeography: an ecological and evolutionary approach[END_REF]). However, when divergence time estimation showed that lineage dispersal must have played a more prominent role than previously thought, parsimony-based approaches like DIVA came under critique [START_REF] Kodandaramaiah | Use of dispersalvicariance analysis in biogeography -a critique[END_REF].

Parsimony techniques use only the branching pattern of a phylogeny as evidence, but are indifferent to time. Thus, a dispersal event is considered the same way whether it occurred on a long or a short branch, i.e. in a long or a short time interval [START_REF] Ree | Prospects and challenges for parametric models in historical biogeographical inference[END_REF]). This changed with the first parametric approach, the dispersalextinction-cladogenesis (DEC) model [START_REF] Ree | A likelihood framework for inferring the evolution of geographic range on phylogenetic trees[END_REF] Figure 1. Phylogenetic patterns expected under processes of range evolution modelled by current methods. Grey and black represent two areas of distribution. The asterisk indicates where range evolution takes place: at speciation (cladogenetic) or on a branch (anagenetic). Full or partial range-copying (sympatry) is not shown. Note that a pattern found in a phylogeny does not imply that an event was actually possible. For example, a barrier could have emerged long before or after a presumed vicariance event. Smith 2008). This model specifically estimated rates of dispersal and extinction, which make those events more likely on longer branches. Parametric models also allowed to incorporate information on the timing of events that may have influenced the evolution of ranges, such as the appearance or disappearance of geological barriers [START_REF] Ree | Prospects and challenges for parametric models in historical biogeographical inference[END_REF]. Furthermore, they estimate probabilities for each possible ancestral range, rather than simply reconstructing one most parsimonious scenario (Sanmartín 2016). DEC allows only one kind of dispersalrange expansion (Fig. 1). In contrast, a model developed for island biogeography (Sanmartín et al. 2008) allowed a lineage to instantly move to a new area, in a process called jump dispersal (Fig. 1). This was suggested to be closer to the reality of island lineages (Sanmartín et al. 2008). This was confirmed by a study which also developed a model integrating jump dispersal (or founder-event speciation) with DEC and a framework to compare different models (Matzke 2014). Parametric models are extensible and can incorporate more complex scenarios, e.g. dispersal rate varying with the carrying capacity of islands (Sanmartín et al. 2008) or with distance between areas (Van Dam & Matzke 2016).

DNA barcoding and metabarcoding

While phylogenetics is a tool to explore biodiversity in time, molecular methods have also been developed to study biodiversity in space. DNA barcoding was coined as a term to designate the automated identification of species by using a specific genomic marker, typically amplified by polymerase chain reaction [START_REF] Hebert | Biological identifications through DNA barcodes[END_REF]. The same new sequencing technologies that promoted the shift to phylogenomics also permitted the analysis of bulk samples that contain a mixture of DNA from different organisms (metabarcoding) (Taberlet et al. 2012b). This allowed studying realms of species diversity that were poorly explored before, for example micro-organisms in natural habitats. Such organisms, which previously had to be cultured -an impossibility for many of them -could now be identified directly from environmental samples (Taberlet et al. 2012a). Environmental metabarcoding has been applied to microbial communities from the human gut [START_REF] Gill | Metagenomic analysis of the human distal gut microbiome[END_REF]) over marine microplankton [START_REF] Bucklin | Metabarcoding of marine zooplankton: prospects, progress and pitfalls[END_REF] to soil fungi at a global scale [START_REF] Tedersoo | Global diversity and geography of soil fungi[END_REF]) and allowed to confirm patterns found for macroorganisms such as biogeographic regionalisation and the latitudinal diversity gradient (e.g. [START_REF] Meiser | Metaanalysis of deep-sequenced fungal communities indicates limited taxon sharing between studies and the presence of biogeographic patterns[END_REF]). An increasing body of research has studied the importance of local environment versus dispersal and biogeographic contingency on structuring microbial communities (e.g. [START_REF] Östman | Regional invariance among microbial communities[END_REF][START_REF] Lindström | Local and regional factors influencing bacterial community assembly[END_REF].

Initial forages into environmental metabarcoding reported astonishing levels of diversity, for example in leaf-associated fungi [START_REF] Jumpponen | Massively parallel 454 sequencing indicates hyperdiverse fungal communities in temperate Quercus macrocarpa phyllosphere[END_REF]. Some of these were later put into perspective when the frequency of errors in first high-throughput sequencing technologies was recognised [START_REF] Quince | Accurate determination of microbial diversity from 454 pyrosequencing data[END_REF]. Newer technologies as well as bioinformatic methods can however minimise or correct for errors [START_REF] Meiser | Metaanalysis of deep-sequenced fungal communities indicates limited taxon sharing between studies and the presence of biogeographic patterns[END_REF]. Other problems are related to what one considers as "species" in an environmental sample. Typically, operational taxonomic units (OTUs) are defined by DNA sequence similarity, but A -Festuca orthophylla occurs in the high Andes of South America. It belongs to the "American II" clade of fine-leaved Loliinae (subfamily Pooideae) that presumably immigrated via dispersal from Eurasia (chapter I). Loliinae are cool-adapted C3 grasses mainly found in the northern hemisphere and are restricted to mountains at tropical latitudes. B -Plateau grassland in the western part of Itremo protected area, Madagascar, dominated by C 4 grasses in Aristidoideae and Panicoideae: Aristida tenuissima (endemic), Loudetia simplex and Schizachyrium sanguineum (red patches). C4 grasses immigrated repeatedly to Madagascar, presumably with the expansion of open habitats beginning in the Late Miocene (chapter II). C -Spiny thicket in arid southwest Madagascar, assumed to be the most ancient biome on the island. It is rich in endemics such as baobabs but also grasses, one of which may be the oldest endemic C 4 grass lineage on the island (Eragrostis chabouisii, Chloridoideae, chapter II). D -Plateau landscape at West Itremo, Madagascar, with open grassland in the foreground, dense gallery forest in the ravine, and open tapia woodland on the hills in the background. Grassland and tapia woodland have similar herbaceous plant communities dominated by C4 grasses, while the forest understorey harbours almost exclusively C3 grasses (chapters II and IV). E -Panicum vohitrense, member of a C3 "Madagascar shade clade" in subfamily Panicoideae that is mainly found in the forest understorey and diversified in Madagascar and nearby West Indian Ocean islands (chapter II). F -Nastus borbonicus, an endemic bamboo (Bambusoideae) from Réunion Island. It belongs to the Hickeliinae, a woody bamboo clade that radiated in the wider Madagascar region and dispersed only once to the African mainland (chapter II). G -Chandrasekharania keralensis (Panicoideae), type specimen at Royal Botanic Gardens, Kew. This monotypic genus and Jansenella form a species-poor tropical C3 lineage mainly found in the Western Ghats of India (chapter III). H -Mountain grassland in Eravikulum National Park, Western Ghats, India. The presence of endemic grazers such as the Nilgiri tahr (pictured) testifies to the old-growth nature of these grasslands. The Western Ghats may have been the origin of a very diverse pantropical C4 grass lineage, Andropogoneae-Arundinelleae (chapter III). I -Brachypodium madagascariense (Pooideae), an endemic C3 grass from the forest understorey in highland Madagascar. It harbours symbiotic fungal endophytes of the genus Epichloë that presumably co-dispersed with their host plant (chapter IV). Image sources: A -Yastay/Wikimedia Commons (CC BY-SA 4.0); F -B.navez/Wikimedia Commons (CC BY-SA 3.0); G -Bord of Trustees, Royal Botanic Gardens, Kew; H -Navaneeth Kishor/Wikimedia Commons (CC BY-SA 3.0); B, C, E and I -Maria S. Vorontsova (with permission); D -author.

Grasses and grasslands

Grass diversity

In this dissertation, I focused on one particular group of plants, the grass family (Poaceae). Grasses are one of the largest known plant families, with around 11,000 species (Kellogg 2015). They have colonised all continents and are found from tropical latitudes to polar regions. The ecological amplitude they occupy is also evident in the habitats they occur in, ranging from moist tropical forests over savannahs to deserts and alpine tundra. Habitats where grasses dominate account for up to 40% of the Earth's terrestrial surface [START_REF] Gibson | Grasses and grassland ecology[END_REF]. The arguably most important cultivated plants -wheat, maize, millets, sugar cane and ricebelong to the family, and many more grass species have local to regional economic importance.

The grass family is thought to have initially evolved in the understorey of tropical forests (Edwards & Smith 2010). With subsequent diversification, different grass clades adapted to various ecological conditions (Fig. 2). Studies have identified two main lineages in the family, namely the BOP (or BEP) and the PACMAD clade (Fig. 3), named after the initials of the subfamilies they comprise (GPWG 2001[START_REF] Gpwg Ii | New grass phylogeny resolves deep evolutionary relationships and discovers C4 origins[END_REF], Soreng et al. 2015). These two clades each include roughly half of all grass species. Grasses in the BOP clade are mainly temperate and have most of their diversity in the high latitudes (Kellogg 2015). However, they also include species in the rice subfamily (Oryzoideae) occurring in tropical to subtropical wetlands and forest understorey as well as two bamboo tribes, Bambuseae and Olyreae, that are mainly tropical. The PACMAD clade, on the contrary, is most diverse at low latitudes, with exceptions e.g. in subfamily Danthonioideae. This group notably includes the grasses that dominate tropical savannahs and other grasslands (Kellogg 2015). 2014), all other information from Kellogg (2015). Nomenclature follows Soreng et al. (2015[START_REF] Soreng | A worldwide phylogenetic classification of the Poaceae (Gramineae) II: An update and a comparison of two 2015 classifications[END_REF].

C4 photosynthesis and tropical grasslands

Grasses, like most plants, evolved under an atmospheric CO2 concentration much higher than today.

Leaf anatomy and photosynthesis was adapted to efficiently assimilate carbon under such conditions [START_REF] Sage | Photorespiration and the evolution of C4 photosynthesis[END_REF]. This efficiency was challenged when atmospheric CO2 concentration dropped beginning around 34 million years ago (Ma), at the start of the Oligocene [START_REF] Zachos | An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics[END_REF]). The leaf enzyme Rubisco which catalyses CO2 assimilation will also metabolise oxygen at low relative CO2 concentration, in a process called photorespiration which leads to a loss of CO2 assimilation efficiency (reviewed in [START_REF] Sage | Photorespiration and the evolution of C4 photosynthesis[END_REF]. Photorespiration is further increased by factors that lower relative CO2 concentration locally in the leaf or decrease Rubisco's specificity for CO2, such as high temperatures and light, or hydraulic stress, e.g. on saline soil. Under this selective pressure, several lineages of plants independently evolved the C4 pathway from the ancestral C3 photosynthesis. This new anatomical and physiological syndrome involves pre-fixing CO2 and concentrating it around Rubisco, thus effectively suppressing photorespiration. C4 photosynthesis is beneficial in hot and seasonally dry climates but costly under high atmospheric CO2 or in temperate climates [START_REF] Sage | Photorespiration and the evolution of C4 photosynthesis[END_REF]. Grasses are the plant family with the highest number of C4 lineages, counting at least 26 origins which all occurred in the PACMAD clade (Fig. 2

; Kellogg 2015).

There is evidence from dated phylogenies that the Oligocene CO2 decline triggered the evolution of C4 photosynthesis in grasses (Christin et al. 2008[START_REF] Vicentini | The age of the grasses and clusters of origins of C4 photosynthesis[END_REF], although older grass age estimates have challenged this (see below). In any case, the diversification and spread of C4 grasses worldwide is estimated to have occurred several millions of years after their emergence (Strömberg 2005, 2011[START_REF] Bouchenak-Khelladi | Diversification of C4 grasses (Poaceae) does not coincide with their ecological dominance[END_REF]. This means that, while low atmospheric CO2 probably facilitated the switch to C4 photosynthesis, other factors contributed to their ecological success and diversification (reviewed by Strömberg 2011). Indeed, the Earth's surface changed dramatically in the Miocene, with the climate getting drier and colder, forests retreating, and fires becoming more frequent. Grasslands expanded both at temperate and tropical latitudes. Fossil stable isotope evidence from paleosols and grazer tooth enamel indicate that in the tropics and warm-temperate regions, these were initially C3 grasslands, which were then gradually colonised and eventually dominated by C4 grasses (Strömberg 2011). This expansion of C4 grassy biomes occurred in the Late Miocene, between 3 and 10 Ma and at variable pace in different locations (Edwards et al. 2010). The switch to C4 photosynthesis and the expansion of C4 grasslands led to an increase of diversification in the PACMAD clade, while concomitantly, the Pooideae subfamily in the BOP clade diversified in cool-temperate regions (Spriggs et al. 2014).

Tropical grasslands have thus been present since at least the Miocene, but in many places they are perceived as non-natural, created through human intervention such as the cutting of trees and the introduction of livestock (Veldman 2016). This is probably due to the fact that the climatic and soil niches of tropical grasslands and forests overlap and they can thus be found as mosaics in the same regions [START_REF] Sankaran | Determinants of woody cover in African savannas[END_REF], Lehmann et al. 2011). Often, C4 grassy biomes have even been classified as degraded forest, which they can resemble in structure (Veldman 2016). Their functioning is however fundamentally distinct from forests (reviewed by Ratnam et al. 2011): grasslands may feature an open tree canopy (then termed savannah) but the understorey is always dominated by grasses, which are predominantly C4 grasses. The grasses are critical to the feedbacks that maintain a savannah, through their biomass accumulation in the wet season, feeding herbivores and fuelling fires in the dry season. Regular fires, along with the action of grazers, are indeed believed to maintain savannah and forest as alternative stable states under similar climatic and soil conditions (Lehmann et al. 2011[START_REF] Hoffmann | Ecological thresholds at the savanna-forest boundary: how plant traits, resources and fire govern the distribution of tropical biomes[END_REF]. Many tropical C4 grasslands are threatened due to human encroachment and climate change but also because of wrong management such as fire suppression and afforestation, based on the misconception as degraded landscapes (Parr et al. 2014, Bond 2016). The presence of native, diverse assemblages of species and endemic radiations of fire-adapted taxa have been used as indicators for old-growth grasslands (Maurin et al. 2014, Veldman 2016).

Age and distribution

The age of the grass family is still a matter of debate. The first estimations of divergence times in Poales, using external monocot fossils for calibration, estimated that the grass family had already diversified at the end of the Cretaceous [START_REF] Bremer | Gondwanan evolution of the grass alliance of families (Poales)[END_REF][START_REF] Janssen | The age of major monocot groups inferred from 800+ rbcL sequences[END_REF].

Later analyses including more genetic markers and grass fossils (Christin et al. 2008[START_REF] Vicentini | The age of the grasses and clusters of origins of C4 photosynthesis[END_REF] found more recent dates, with a BOP-PACMAD divergence at between 50 and 60 Ma and C4 origins compatible with the Oligocene CO2 decline (see above). These estimates were again challenged by the discovery of grass microfossils from the Late Cretaceous, which, when assigned to tribe Oryzeae, suggest early divergences in the family roughly 20 million years older [START_REF] Prasad | Late Cretaceous origin of the rice tribe provides evidence for early diversification in Poaceae[END_REF]). An evaluation of different calibration approaches in grasses concluded that ages of macrofossils are more compatible with estimates based on external angiosperm ages, considered relatively well constrained (Christin et al. 2014). The authors concluded that ages based on old microfossils cannot be dismissed, but are best treated as alternative hypothesis at this time. Under both hypotheses however, the diversification of the large BOP and PACMAD clades would have occurred after the disintegration of Gondwana in the mid-Cretaceous. Thus, lineage dispersal between continents must have occurred repeatedly for the grasses to have reached their almost cosmopolitan distribution (Bouchenak-Khelladi et al. 2010). Indeed, a history of frequent dispersals has been inferred for clades with disjunct distributions, such as the temperate Hordeum (Blattner 2006), Loliinae (Inda et al. 2008) or the mainly south temperate Danthonioideae (Linder et al. 2013).

Symbiosis with endophytes

Throughout their distribution, grasses interact with other organisms. Like almost all plants, they have microbial symbionts, including fungi [START_REF] Rodriguez | Fungal endophytes: diversity and functional roles[END_REF]). Endophytes -microbes growing within a plant host without harming it (Wilson 1995) -associating with grasses have attracted particular research interest. In the fungal family Clavicipitaceae (Ascomycota), endophytes of the genus Epichloë (synonym Neotyphodium, [START_REF] Leuchtmann | Nomenclatural realignment of Neotyphodium species with genus Epichloë[END_REF] have specialised on grasses (Schardl et al. 2004). Growing in the leaves without causing any symptoms through most of their growth cycle, many species have evolved a close mutualistic relationship with their grass host: they protect it against herbivores through the production of alkaloids and can increase resistance to drought and certain pathogens (reviewed by Clay & Schardl 2002). Through these attributes, the fungi can even affect the structure of the food chain (Omacini et al. 2001) and the plant community (Clay & Holah 1999) their host belongs to. As the mutualistic Epichloë species are seedborne and transmitted vertically, they have co-evolved closely with their hosts, even leading to co-divergence of lineages (Clay & Schardl 2002).

The Epichloë endophytes are restricted to temperate grasses of subfamily Pooideae but are found on most continents (Clay & Schardl 2002). In a survey of tropical forest grasses in Panama, they were absent (Higgins et al. 2011). Many more species of endophytes associate with grasses, although presumably more loosely than the Epichloë endophytes (Sánchez [START_REF] Márquez | Non-systemic fungal endophytes of grasses[END_REF]. Grass endophytes in tropical regions remain largely unknown, but the latitudinal diversity gradient with higher diversity in the tropics is also thought to apply to endophytes [START_REF] Arnold | Are tropical fungal endophytes hyperdiverse?[END_REF]. A mutualistic relationship has also been demonstrated between a panicoid grass, Dichanthelium lanuginosum, and a non-Epichloë endophyte (Redman et al. 2002), suggesting the existence of further unknown co-evolutionary systems, with potential community-wide impacts. Despite the importance of grasslands and herbivory in the tropics (see above), basic questions remain to be answered on tropical grass endophytes. These include whether dispersal limitation and regionalisation play an important role, and whether host and environmental factors are strong drivers of community structure, such as shown in tree phyllosphere fungi (Cordier et al. 2012, Zimmerman & Vitousek 2012[START_REF] Bálint | Host genotype shapes the foliar fungal microbiome of balsam poplar (Populus balsamifera)[END_REF].

Dissertation outline

In the work I present here, I have used molecular tools to study the biogeography of grasses, the assembly of tropical grasslands, and the community structure of grass endophytes. All parts integrate the evolutionary history of grass lineages as a major determinant of current patterns. In the first chapter, I describe an analysis of dispersal history in a temperate clade of grasses found in isolated areas at tropical latitudes. Distance was found to be a major determinant of dispersal, while ecological differences between grass clades had a minor effect. In the second chapter, I present a study of the age and biogeographic history of the grass flora of Madagascar. Results show that it has predominantly African origins, features two diverse in situ radiations of bamboos and forest grasses, and is characterised by repeated immigration and speciation of C4 grasses since the Miocene. In the third chapter, I show how phylogenomic methods allowed me to place three enigmatic Asian C3 species in the grass phylogeny. Their position suggests that a very large, pantropical C4 grass clade has its origin in India. In the fourth and last chapter, I describe a metabarcoding method to study communities of grass endophytes in Madagascar. Results are preliminary and highlight methodological limitations but attest the presence of Pooideae-associated Epichloë endophytes in Madagascar.

Abstract

Dispersal of lineages depends on specific ecological requirements as well as on generalised factors such as distance and barriers. The temperate grass subtribe Loliinae (Poaceae: Poeae) has two main subgroups, broadleaved (BL) and fine-leaved (FL) Loliinae, that differ in phenotypic syndrome and ecology and have both widespread, disjunct distributions in the northern and southern hemispheres. Previous studies have inferred phylogenetic relationships in this group and developed scenarios for its historical biogeography. Here, I used parametric models of range evolution combined with stochastic mapping to test the influence of distance, disjunction type, and phenotypic differences on dispersal rates. A model integrating founder events and scaling of dispersal by shortest distance between areas performed best amongst a set of alternative models and recovered a mean of 83 dispersal events. Overall dispersal rates were significantly higher in BL than in FL. Per-route dispersal rates showed a significant negative exponential relationship to shortest distance but were not affected by phenotypic syndrome or disjunction type. I conclude that Loliinae originated in the northern hemisphere, in agreement with previous studies, and evolved through recurrent range expansions and founder-event dispersals. Higher competitive ability, potentially related to the broad-leaved syndrome (i.e. tall, strongly rhizomatous plants, long-living individuals, occupancy of more stable habitats), may explain higher inferred dispersal rates in BL compared with FL Loliinae. However, the dominant factor impacting dispersal in both BL and FL Loliinae is the distance between suitable areas.

Introduction

Lineage dispersal across large distances is seen as a major process in the evolution of organismal diversity and distribution, especially in plants [START_REF] Nathan | Long-distance dispersal of plants[END_REF], Crisp et al. 2011).

Studies using molecular phylogenetics have revealed its importance especially in the southern hemisphere, where dispersal occurring well after the split-up of the supercontinent has frequently been recovered (e.g. [START_REF] Sanmartín | Southern hemisphere biogeography inferred by event-based models: plant versus animal patterns[END_REF]. In plant groups with a global distribution, dispersal clearly played a key role, especially where plants are adapted to conditions found in widely disjunct regions, such as a temperate climate (e.g. Blattner 2006, Linder et al. 2013). Indeed, biome compatibility is thought to be a major determinant of dispersal (Donoghue 2008). However, factors independent of the species' ecology, such as the directionality of potential dispersal vectors (e.g. winds or ocean currents (e.g. [START_REF] Renner | Plant dispersal across the tropical Atlantic by wind and sea currents[END_REF], Sanmartín et al. 2007) or the distance between suitable areas (e.g. Linder et al. 2013, Van Dam & Matzke 2016) have also been shown to impact the frequency of dispersals.

1 The results of this chapter have contributed to the work led by P. Catalán and developed by M. Minaya (University of Zaragoza, doctoral dissertation 2015) and have been published in an article entitled "Contrasting dispersal histories of broad-and fine-leaved temperate Loliinae grasses: range expansion, founder events, and the roles of distance and barriers" in Journal of Biogeography (2017, vol. 44: pages 1980[START_REF] Kidwell | Lateral transfer in natural populations of eukaryotes[END_REF], DOI: 10.1111 My contribution was an analysis of range evolution with models integrating distance and founder-event speciation, stochastic mapping, and statistical analysis of dispersal rates (all presented here), and the writing of the corresponding parts of the article.

The almost cosmopolitan grass family (Poaceae) includes clades of grasses adapted to temperate climates and found in widely separated areas of the northern and southern hemisphere. The subtribe Loliinae (Pooideae: Poeae) is one of the largest among these, with over 600 species in the polyphyletic fescues (Festuca) and allied genera [START_REF] Catalán | Phylogeny and evolution of Festuca L. and related genera of subtribe Loliinae (Poeae, Poaceae)[END_REF]). These are found mainly in the northern hemisphere, but also in the temperate southern hemisphere (e.g. Patagonia and Australasia) and mountain ranges at tropical latitudes (e.g. the Andes and the East African Rift mountains) [START_REF] Catalán | Phylogeny and evolution of Festuca L. and related genera of subtribe Loliinae (Poeae, Poaceae)[END_REF]. Phylogenetic studies showed that the subtribe includes two main lineages encompassing the majority of species, the "broadleaved" (BL) and the "fine-leaved" (FL) Loliinae, and a smaller "intermediate" lineage (Catalán et al. 2007, Inda et al. 2008). Their names reflect their phenotypes: BL Loliinae are mostly robust, perennial, and with a well developed rhizome, while FL Loliinae tend to be more slender, mostly annual, and without vigourous rhizome [START_REF] Catalán | Phylogeny and evolution of Festuca L. and related genera of subtribe Loliinae (Poeae, Poaceae)[END_REF]. The "intermediate" lineage has a BL phenotypic syndrome, but is sister to the FL lineage, which together are sister to the BL Loliinae (Catalán et al. 2007, Inda et al. 2008). Phenotypic differences correspond to ecology, with BL tending to be more competitive and preferring mesic, stable habitats, while FL are rather colonist and found under harsher or more unstable conditions [START_REF] Catalán | Phylogeny and evolution of Festuca L. and related genera of subtribe Loliinae (Poeae, Poaceae)[END_REF]. FL Loliinae also have higher rates of molecular evolution [START_REF] Catalán | Phylogeny and evolution of Festuca L. and related genera of subtribe Loliinae (Poeae, Poaceae)[END_REF]. Inda et al. (2008) performed the first historical biogeographic analysis of Loliinae. They estimated a crown age of around 13 million years (Ma) for the subtribe and a dispersaldominated history with a Eurasian origin of both BL and FL Loliinae. The dissertation of Minaya (2015) extended this work, including a more comprehensive sample of species with many southern hemisphere taxa previously unsampled. Minaya recovered five new southern hemisphere lineages within Loliinae, three in BL and two in FL. He used a new set of macroscopic and phytolith fossils for calibration and estimated an age considerably older that that of Inda et al. (22.5 Ma). Implementing the dispersal-extinction-cladogenesis model (Ree & Smith 2008), he estimated additional dispersals: notably, long-distance dispersal events from South America to Tropical Africa, from Eurasia to Australasia, across the Antarctic between South America and Australasia, and between the Arctic and the Antarctic, were inferred. Minaya also suggested that BL were more successful at colonising adjacent areas, while FL more frequently crossed large distances.

Dispersal can be affected by the ecology of the species as well as unrelated, generalised factors such as distance. New parametric methods in biogeography allow to statistically test the importance of such factors (Van Dam & Matzke 2016). They can also include founderevent speciation, typical for island-like scenarios, and distinguish it from range expansion (Matzke 2014). In this chapter, my goal was to build on the work of Minaya (2015) by applying these recently developed models of range evolution. My main questions were the following: (i) Which role did distance and different modes of dispersal play in the biogeographic history of Loliinae? (ii) Which type of distance (centre vs. shortest) between areas of distribution would best explain lineage dispersal? (iii) Do dispersal rates differ between BL and FL Loliinae, and across oceanic vs. terrestrial barriers?

Materials and methods

Analysis of range evolution I used the dated Loliinae phylogeny of Minaya (2015), which was estimated from molecular data both from the nuclear (internal transcribed spacer region) and the chloroplast genome (trnT-L and trnL-F spacers) and dated with fossil calibration points. It includes 214 accessions of 178 species representing the global distribution of the subtribe (Minaya 2015). Twelve operational areas (OAs) as defined by Minaya were used for range evolution analysis: South Africa, Madagascar & Mascarenes, Tropical Africa, Mediterranean, Irano-Turanian-Himalayan, North Eurasia, Australasia North & Central America, Northern South America, Southern South America, Macaronesia and Hawaii.

Maximum Likelihood analysis of range evolution in the BioGeoBEARS package (Matzke 2013) under R version 3.3.1 (R Core Team 2016), was used to implement the dispersalextinction-cladogenesis (DEC) model of Ree & Smith (2008) and extensions thereof. I compared the basic DEC model, which assumes range expansion on branches as the only mode of dispersal, to models adding founder-event dispersal at speciation (DEC+j; Matzke 2014) or a distance-scaling parameter x (DEC+x; Van Dam & Matzke 2016), and models integrating both parameters (DEC+j+x). For the distance-dependent models (DEC+x, DEC+j+x), I tested both approximate pairwise shortest distances between OAs and pairwise distances between centres of each OA, calculated as Vincenty ellipsoid distances in the R package geosphere (Hijmans 2016) (Table A-I.1, annex). I assumed that the two types of distance roughly represent geographical distances through the time period studied (Late Oligocene to present).

A total of six models (DEC, DEC+j, DEC+x shortest distances, DEC+x centre distances, DEC+j+x shortest distances, DEC+j+x centre distances, see Table I.1) were thus optimised and compared, using the maximum clade credibility tree obtained by Minaya (2015) with outgroups removed. Only one accession was kept per species, except in the paraphyletic Festuca abyssinica that was represented by three accessions; exclusion of any accession here is unlikely to modify the ancestral areas estimated as all the species of the clade are distributed in the same OA (Tropical Africa, see Results). Two areas were assumed to be the maximum range size, based on current distribution patterns (Sanmartín 2003). I compared model performance with the Akaike information criterion (AIC) and the Bayesian information criterion (BIC) and estimated relative likelihoods for ancestral areas at nodes under all models.

Dispersal counts and rates

To infer the number and rates of dispersals, I used stochastic mapping in the BioGeoBEARS package (Matzke 2016). I ran 1000 simulations for both the best-performing model (DEC+j+x with shortest distances, see Results) and the baseline DEC model and recovered the number of range expansions and founder-event dispersals for each branch and node, respectively. This allowed me to calculate and compare per-lineage dispersal rates for BL and FL Loliinae, by dividing the number of dispersals by median stem age and the number of tips per lineage. For BL, I calculated dispersal rates for both the main BL clade alone and for the BL + "intermediate" clade, in the latter case dividing by the older BL stem age.

Dispersal rates (range expansion, founder-event, and total) were also calculated for each route, in each direction, and for BL (including the "intermediate" clade) and FL, yielding N = 264 data points (most of them zero). Quasi-Poisson regression in R, with a logarithmic link function, was used to test the relationship between dispersal rates and distance, using either shortest or centre distance as predictors, as well as lineage (BL or FL) and disjunction type (terrestrial or oceanic). For each dispersal rate and range evolution model, I fitted both a global regression model with distance, lineage, disjunction type and their interactions as predictors and a reduced model with distance as sole predictor.

Results

The DEC+j+x model of range evolution with shortest distances clearly outperformed the other five models in ML estimation, accounting for >0.99 of AIC and BIC weights (Table I.1). Figure 1 shows the relative likelihoods of ancestral areas at each node under this model. Estimations were similar for other models, but these assumed more widespread ancestral ranges when founder-event dispersal was excluded (i.e. under DEC and the DEC+x models, not shown). Ma). Geological time scale is shown at the bottom. OAs assigned to each selected species (A to L) and the major lineages are indicated to the right of the tree. The inferred range expansions (black dots) and founder events (crosses) are indicated on branches and at nodes of the tree, respectively, with symbol size referring to the frequency of an event inferred in 1000 simulations.

A mean of 83 dispersal events (95% confidence interval [CI] 77-88) was recovered for Loliinae with stochastic mapping under the best model, DEC+j+x with shortest distances, compared to 72 (CI 67-77) under the baseline DEC model (Fig. I.2a). DEC+j+x allowed to distinguish between range expansion and founder-event dispersal, of which 28 (CI 24-32) and 55 (CI 48-62) events were estimated, respectively (Fig. I.2a). Range expansion, founderevent, and total dispersal rates were significantly lower for FL than for BL Loliinae, both under DEC and DEC+j+x and regardless of whether the intermediate clade was included in BL or not (Mann-Whitney U test, P < 0.001 in all cases; Fig I .2b).

Per-route dispersal rates showed a significant relationship to the shortest distance between OAs, and a negative exponential curve provided good fit under a quasi-Poisson regression model for range expansion, founder-event, and total dispersal rates under DEC and DEC+j+x (P < 0.001 for shortest distance in all cases; When shortest distance was taken into account, phenotypic syndrome (BL or FL), disjunction type (oceanic or terrestrial), and interactions had no significant effects on per-route dispersal rates (P > 0.05 in all cases; Table A-I.2). In regression on distance between OA centres, the results were less clear: no variable was significant, when tested together, for founder-event dispersal rates (DEC+j+x), whilst only disjunction type was significant for range expansion and total dispersal rates (Table AI.2, Fig. A-I.1). Centre distance was significant in all cases when tested alone.

Discussion

Historical biogeography of Loliinae

The biogeographical analyses of the Loliinae suggest recurrent colonizations through range expansions and founder-event dispersals that predominantly occurred within the northern hemisphere and from the northern to the southern hemisphere, but also within the southern hemisphere, and from S. America and S. Africa to N. and C. America (Fig. I.1). This is concordant with the complex scenario of neo-and re-colonisations suggested by Minaya (2015). Similar long-distance lineage dispersal patterns have also been suggested for other temperate pooids (Hordeum, Blattner 2006) and austral-temperate grasses (danthonioids, Linder et al. 2013). The strong support found here for a range evolution model including founder-event speciation, typical of island clades (Matzke 2014), is in line with the picture of the cool-temperate Loliinae lineages moving about between suitable, often very distant areas. In agreement with Inda et al. (2008) and Minaya (2015), my biogeographical analysis lends support to an ancestral northern hemisphere distribution of Loliinae, but with uncertainty between Northern Eurasia, the Mediterranean region, North America, or a widespread distribution (Fig. I.1).

Dispersal rates: distance, barriers and differences between broad-and fine-leaved Loliinae

The analysis of range evolution selected a model including scaling by shortest distance between areas as the best one (Table I.1). Shortest distance thus seems to provide a reasonable approximation of the true dispersal corridors, which likely depend on complex combinations of wind direction, ocean currents, animal migration routes, and suitable habitat patches. The regression of per-route dispersal rates, inferred through stochastic mapping, against shortest distance also shows a good fit with a negative exponential distribution. Only if one excludes the largest distances (>14,000 km) where dispersal is effectively zero, a fat-tailed dispersal kernel [START_REF] Nathan | Long-distance dispersal of plants[END_REF]) may be distinguished. Overall, distance appears to be the major determinant of successful dispersal, while the type of disjunction (oceanic vs. terrestrial) was not supported as significant when shortest distance was included as predictor.

I recovered higher overall dispersal rates for BL than FL Loliinae under both the best DEC+j+x and the simplest DEC models. In contrast, per-route dispersal rates did not reveal a Figure I.3. Mean per-route dispersal rates in Loliinae, inferred with biogeographical stochastic mapping, plotted against the shortest distance between respective OAs. The DEC model, not including a distance effect, and a DEC+j+x model, scaling dispersal rates by shortest distance, were both used for 1000 simulations on the phylogenetic tree inferred by Minaya (2015). Dispersal rates were calculated per route, for each direction, for BL (including Intermediate; black) and FL (grey) Loliinae lineages, yielding 264 data points. Quasi-Poisson regression of dispersal rates on shortest distance showed a significant negative relationship for each range evolution model and type of dispersal (regression curve in blue, slope value is log-scale). X-axis shows geographical distance in km. Phenotypic syndrome (broad-vs. fine-leaved) and disjunction type (oceanic vs. terrestrial) had no significant effect on dispersal rates when distance was accounted for. The phenotypic syndromes of BL and FL Loliinae are associated with different evolutionary rates and adaptive capabilities [START_REF] Catalán | Phylogeny and evolution of Festuca L. and related genera of subtribe Loliinae (Poeae, Poaceae)[END_REF][START_REF] Catalán | Phylogeny and evolution of Festuca L. and related genera of subtribe Loliinae (Poeae, Poaceae)[END_REF]. Perennial Loliinae show significantly lower molecular evolutionary rates than annual Loliinae [START_REF] Catalán | Phylogeny and evolution of Festuca L. and related genera of subtribe Loliinae (Poeae, Poaceae)[END_REF]. Relative rate ratios support the minimum-generation-time hypothesis, implying the predominance of stabilizing selection in the mostly strong-rhizomatous perennial BL Loliinae versus more rapid adaptive evolution in the slender perennial and annual FL Loliinae [START_REF] Catalán | Phylogeny and evolution of Festuca L. and related genera of subtribe Loliinae (Poeae, Poaceae)[END_REF][START_REF] Catalán | Phylogeny and evolution of Festuca L. and related genera of subtribe Loliinae (Poeae, Poaceae)[END_REF]). This pattern is likely a consequence of the colonist syndrome of the FL Loliinae, which are, in general, better adapted to cool and dry ecological conditions than the BL Loliinae [START_REF] Catalán | Phylogeny and evolution of Festuca L. and related genera of subtribe Loliinae (Poeae, Poaceae)[END_REF], Catalán et al. 2007). The colonist syndrome of the FL Loliineae, together with the existence of suitable habitats along the Andean corridor, Patagonia and the circum-Antarctic islands, might also explain why the FL lineages have spread more frequently in S. America and the South Pacific, but not in Africa, where BL ancestors have established more frequently in less abundant, but more stable habitats (Minaya 2015). This asymmetric dispersal pattern has resulted in the FL and BL Loliinae having, respectively, five and two lineages with most of their current species distributed in the southern hemisphere (Fig. I.1). Given relatively similar dispersal conditions for both lineages, BL Loliinae may be more competitive, both by being strongly rhizomatous, long-living plants, and by being adapted to more stable habitats than the more vagile FL Loliinae, which are less robust, short-living plants and usually adapted to less stable habitats. On the other hand, dispersal limitation by distance appears to be strong in both BL and FL Loliineae and would explain why no difference in dispersal rate per route was found between the two phenotypes once distance was taken into account.

Conclusion

This biogeographical analysis infers that the biogeographical history of the Loliinae began in the northern hemisphere and was shaped by frequent dispersals, both through founder events and through range expansion. Distance emerges as the overall most important factor in determining successful dispersal, whether across oceans or continents, with shortest distance between areas showing the best fit with the phylogenetic tree and the estimated dispersal rates. BL Loliinae appear more successful in the overall dispersal rates than FL Loliinae, presumably because of a more competitive life strategy. Nevertheless, dispersal per route is limited by distance in a similar fashion for both BL and FL Loliinae. 3 Chapter II: Grass diversification in Madagascar1

Abstract

Grasses (Poaceae) are found in all major habitats of Madagascar and have a particular importance in C4 grasslands, whose origins are controversial. We aimed to estimate the number, age and origins of endemic grass lineages in the Madagascar region, and to compare the diversification of C3 and C4 taxa. We estimated 11 timecalibrated molecular phylogenies including 73% of Madagascar's known grass flora (65% of endemics), using two calibration scenarios. Integrating the available sequences from worldwide grass species, a total of 1928 accessions were analysed. We tested range evolution models, estimated ancestral ranges, and compared the patterns of lineage accumulation between endemic C3 and C4 grasses. We recovered 69 lineages endemic to or with an estimated origin in the Madagascar region, 25 of them C3 and 44 C4. Range evolution analysis suggests widespread distance-scaling of dispersal and strongest historical links to Africa. Extant grass diversity largely accumulated since the Miocene, with parallel increases in C3 and C4 taxa. Two large C3 groups in the "Forest shade clade" (Paniceae: Boivinellinae) and the bamboos (subtribe Hickeliinae) have an estimated origin in the Madagascar region. Divergences and crown ages of endemic C4 lineages largely coincide with the Miocene grassland expansion. We conclude that Madagascar's extant grass flora is the result of multiple overseas dispersals, predominantly from Africa, and diversified from the Miocene onwards. C3 grasses are characterised by two large presumed in situ radiations of shade grasses in the Paniceae and bamboos. Endemic C4 lineages result from twice as many immigration events, resulting in smaller clades. Ages of C 4 lineages are consistent with a Pliocene or Late Miocene origin of grasslands in Madagascar, but estimating the nature and expanse of such early grasslands will require further research.

Introduction

Madagascar's biodiversity is exceptional in its richness and endemism, and understanding the assembly of this island biota has been a major goal of biogeography. Molecular phylogenetics and time calibration have shown that despite Madagascar's long isolation (from mainland Africa since around 140 Ma and India since 88 Ma), the overwhelming majority of currentday endemics appear to be "neo-endemics" resulting from overseas immigration rather than ancient Gondwanan vicariance (Yoder & Nowak 2006, Buerki et al. 2013). This has refined ideas on the "evolution in isolation" of Malagasy lineages, yielding the picture of a biota more dynamic and, in many cases, younger than assumed before.

The flora of Madagascar, with over 80% endemism (Madagascar Catalogue 2013), is an assemblage with mixed affinity. It has the strongest taxonomic links with continental Africa, and with the surrounding West Indian Ocean islands of the Comoros, Seychelles, and Mascarenes, which may be considered part of a wider Madagascar region (Buerki et al. 2013). There are also evident links to the floras of India and Southeast Asia [START_REF] Schatz | Malagasy/Indo-Australo-Malesian phytogeographic connections[END_REF], Buerki et al. 2013). Within Madagascar, a large diversity of habitats and vegetation types, ranging from high-mountain temperate vegetation to tropical humid forests and sub-arid spiny thickets [START_REF] Humbert | Destruction d'une flore insulaire par le feu : principaux aspects de la végétation à Madagascar[END_REF], Moat & Smith 2007) may partly explain the exceptional levels of taxonomic richness.

Grasses (Poaceae) are one of the largest plant families in Madagascar, with roughly 550 recorded species (Vorontsova et al. 2016). They occur in all major terrestrial habitats. The proportion of endemic grass species is 40%, which is lower than that of most other plant families in Madagascar but higher than the average grass endemism for islands of similar size (Vorontsova et al. 2016). The age of the family is still a matter of debate, but different methods of time calibration and chloroplast vs. nuclear data place the diversification of its large crown group (the BOP-PACMAD clade) in the Late Cretaceous to Early Eocene, after Gondwana break-up (Christin et al. 2014). The cosmopolitan distribution of grasses must therefore be the result of recurrent dispersal between continents. Bio-and phylogeographic work has shown that the availability of suitable climatic conditions played a major role in allowing grasses to successfully colonise new continents (Linder et al. 2013, Visser et al. 2014[START_REF] Lundgren | Photosynthetic innovation broadens the niche within a single species[END_REF]. The multiple evolution of C4 photosynthesis in grasses, first occurring in the Oligocene (Christin et al. 2008[START_REF] Vicentini | The age of the grasses and clusters of origins of C4 photosynthesis[END_REF], and the expansion of grasslands in the Miocene were major drivers of grass diversification (Spriggs et al. 2014). This global Miocene grassland expansion occurred roughly between 3 and 8 Ma, but the exact timing differed between continents. It strongly modified biomes in the tropics, where C4 grasses became dominant in open areas (Edwards et al. 2010). C3 grasses, outcompeted under warm, high-light conditions, are mainly restricted to more humid and cooler microclimates in Madagascar and other tropical regions [START_REF] Nanjarisoa | Poaceae checklist of the Itremo Massif records endemic plateau grasses[END_REF][START_REF] Edwards | Climate, phylogeny and the ecological distribution of C4 grasses[END_REF].

C4 grasses, keystone species in open areas, are at the heart of the debate on the origin of the grasslands of Madagascar. These are now the dominant vegetation type on the island, in particular on the central plateaus (Moat & Smith 2007). Many authors interpreted these grasslands as secondary, created through cutting, grazing and fire after human colonization (Perrier de la [START_REF] Perrier De La Bâthie | La végétation malgache[END_REF][START_REF] Humbert | Destruction d'une flore insulaire par le feu : principaux aspects de la végétation à Madagascar[END_REF][START_REF] Koechlin | Flora and vegetation of Madagascar. Biogeography and ecology in Madagascar[END_REF]. In contrast, several lines of evidence suggest that at least some grasslands may be ancient, primary vegetation. These include grassland endemics (Bond et al. 2008, Vorontsova et al. 2016), pre-human pollen and charcoal deposits indicative of open habitats with natural fires (Burney 1987[START_REF] Burney | Theories and facts regarding Holocene environmental change before and after human colonization. Natural change and human impact in Madagascar[END_REF], Gasse & Van Campo 1998) and Sporormiella deposits suggesting presence of megaherbivores (Burney et al. 2003). Under this scenario, grasslands in Madagascar would be a regional outcome of the global Miocene grassland expansion (Bond et al. 2008). Around 358 C4 grass species, with roughly 100 endemics (28%), are known in Madagascar, and many are regionally restricted (Vorontsova et al. 2016). Phylogenetic diversity of grassland communities was found to be negatively associated with grazing and trampling but independent of fire frequency, suggesting an endemic, fire-adapted grass flora (Vorontsova et al. 2016). Endemic clades of C4 grasses would also support a natural origin of grasslands, but few of the endemic C4 grass species have yet been included in phylogenetic analyses.

C3 grasses in Madagascar are overall less diverse but have a significantly higher proportion of endemics than C4 grasses (roughly 120 of 175, 68%; see checklist in Vorontsova et al. 2016). They include at least one phylogenetically isolated lineage (Panicoideae: Lecomtella; Besnard et al. 2013) as well as endemic and diverse genera of forest grasses and bamboos [START_REF] Dransfield | Poaceae, Bambuseae, bamboos. The Natural History of Madagascar[END_REF][START_REF] Vorontsova | Endemic non-bambusoid genera of grasses (Poaceae) in Madagascar: review of current knowledge[END_REF]. C3 habitats in Madagascar and surrounding islands include the high mountains, the forest understorey, and various sheltered locations under rocks or other plants, including other grasses. The higher endemism in C3 grasses suggests that they may belong to lineages which had more time for diversification or, alternatively, higher diversification rates than C4 grasses.

In this study, we aimed to infer the diversification history of grasses in Madagascar, using molecular phylogenetics and dating combined with range evolution analysis. We first estimated the number and ages of endemic grass lineages in Madagascar. Second, by estimating ancestral areas, we sought to uncover the main biogeographical links of the Madagascan grass flora and to test if the region was only a "sink" for immigrant taxa or if in situ diversification and dispersal to other regions also occurred. Third, we specifically compared endemic C3 and C4 lineages, to see whether the ages of C4 taxa were in line with a Miocene expansion of grasslands, and to test whether the C3 and C4 grass floras differed in age or lineage accumulation dynamics.

Materials and Methods

Taxon sampling, molecular biology, and data retrieval

We aimed to analyse a set of molecular data representative for the grass flora of Madagascar and the West Indian Ocean region and included available as well as new molecular data1 . New sequence data were produced by PCR and Sanger sequencing or by high-throughput sequencing (see Annex A-II for details). We used three to five chloroplast markers (ndhF, rbcL, andtrnK-matK, GPWG II 2012, Taylor et al. 2012; adding the rpl16 and rps16 introns for the slow-evolving Bambusoideae, see A-II). Sequences were organised in 11 datasets corresponding to major grass clades [START_REF] Gpwg Ii | New grass phylogeny resolves deep evolutionary relationships and discovers C4 origins[END_REF]Kellogg 2015;Soreng et al. 2015): Oryzoideae, Bambusoideae, Brachypodieae, Poeae, Aristidoideae, Panicoideae (focusing on the "outlying Panicoideae" and Lecomtella, representing the large Andropogoneae-Arundinelleae, Paniceae and Paspaleae clades with two taxa each), Paniceae, Andropogoneae-Arundinelleae, Arundinoideae-Micrairoideae, Chloridoideae, and Danthonioideae. For each clade, we added sequence data available from GenBank. In total, an estimated 73% of the known species diversity in Madagascar, and 65% of the endemics are represented.

Phylogenetics, dating, and analysis of endemic clades

DNA sequences were aligned by marker for each clade using MAFFT v.7 (Katoh & Standley 2013). After manual inspection and trimming of poorly aligned ends, alignments were concatenated by clade and contained between 18 (Brachypodieae) and 516 (Paniceae) accessions, for a total of 1928. Maximum Likelihood (ML) and Bayesian phylogenetic analyses were performed with RAxML (Stamatakis 2014) and BEAST2 (Drummond et al. 2006, Bouckaert et al. 2014, Rambaut et al. 2014), respectively, on the Cipres platform (Miller et al. 2012). We used two alternative, secondary calibrations: ages based on external angiosperm calibration and ages accounting for controversial phytolith fossils (Christin et al.

2014, see Table A-II.2).

As estimates of the age of the Madagascan grass flora, we obtained the median ages and 95% HPD intervals for stem and crown of strictly endemic lineages (i.e. containing only endemic taxa) recovered in the MCC trees under both age calibrations. Lineages were scored as C3 or C4, based on the checklist of Osborne et al. (2014, see Table A-II.3). Details on alignment, phylogenetic models, and dating priors can be found in Annex A-II.

Analysis of range evolution

ML analysis of range evolution with the package BioGeoBEARS (Matzke 2013) in R was used to estimate the dispersal history between the Madagascar region and seven other areas: Tropical Africa, Southern Africa, Eurasia plus North Africa, the Indian subcontinent, Southeast Asia plus Australasia, North America, and the Neotropics. Species distribution was scored according to the World Checklist of Selected Plant Families (WCSP; Clayton et al. 2016). For each clade, we compared four range evolution models: (i) the dispersalextinction-cladogenesis (DEC) model (Ree & Smith 2008); (ii) a DEC model expanded with j, a relative weight for founder-event speciation (DEC+j; Matzke 2014); (iii) an expanded DEC model scaling dispersal probabilities by distance between areas to power x (DEC+x; Van Dam & Matzke 2016); and (iv) a model integrating both j and x (DEC+j+x).

The best-fitting model was used to estimate ancestral areas and identify lineages with an estimated origin in the Madagascar region (i.e. with a marginal probability >0.5 for the region). We summed marginal probabilities for areas ancestral to clades estimated present in the Madagascar region, reflecting the origins of jump dispersals resulting in speciation in Madagascar. We correlated these figures with distance to Madagascar, calculated as Vincenty ellipsoid distance (Hijmans 2016) between approximate centres. This was compared to current-day occurrence counts in other areas of species native but not endemic to Madagascar, reflecting recent range expansions to or from Madagascar. We also traced the accumulation of C3 and C4 grass lineages in the Madagascar region through combined speciation and immigration with a lineage-through-time analysis: using MCC trees with median ages under external age calibration, we counted the number of C3 and C4 lineages in each 1 Myr time bin and weighted them by their marginal probability to occur in the region. Details on range evolution analysis can be found in Appendix A-II; Table A-II.4 contains area distances.

Results

Across the 11 phylogenies we estimated, we recovered 96 lineages that include only taxa strictly endemic to the Madagascar region (Table II.1). After accounting for common origins suggested by range evolution analysis, these strictly endemic lineages cluster in 69 lineages with an estimated origin in the region. Most of these contain only endemics, but some also include non-endemic or non-Madagascan taxa. C4 lineages account for roughly twice as many Madagascar origins as C3 lineages (44 vs. 25, Table II.1 The two alternative age calibrations yielded different estimates, but these were close for more recent divergences, where the difference was mostly 1-3 Ma between the two median age estimates (Fig. 1 The detailed plots of the individual phylogenies with support values and ancestral area probabilities have not been included in the annex for formatting issues (the largest phylogeny includes 516 accessions). They will be available with the online article as supplementary information. All alignments and phylogenies are available on TreeBase (study number S21602, reviewer access: http://purl.org/phylo/treebase/phylows/study/TB2:S21602?xaccess-code=f8c9b299773662ae3f7625bb51f0520e&format=html)

The DEC+j+x model of range evolution ranked highest by AICc in 8 of 11 clades analysed (Table S2.6 DEC or from the respective best model (one-sided Spearman test, p = 0.48 and p = 0.13, respectively). Tropical Africa, North America, and the Neotropics were mainly estimated as source regions for C4 taxa (with C4 taxa accounting for 56, 63, and 76%, respectively, of the summed ancestral area probabilities), while Eurasia and Southern Africa are predominantly C3 sources (with 78 and 82%, respectively). Modern-day distribution ranges of non-endemics largely mirror the ancestral dispersal patterns, but India has a markedly higher share of occurrences compared to its estimated importance as ancestral area, while the relationship is inverse for the Neotropics (Fig. II.4). The proportion of C4 species in each area is higher and less variable than for ancestral areas, ranging from 68 to 89%. The number of occurrences is negatively correlated with distance to Madagascar, whether tested for C3 and C4 species separately, or combined (all p < 0.05, one-sided Spearman test).

Eleven clades with nested non-Madagascan species had a relative ancestral area probability >0.5 for the Madagascar region estimated with both the respective best model and DEC, of which seven have strong clade support (Table A-II.6). The largest and oldest is a C3 group in the "Forest shade clade" (Fig. II.5) with a relative probability of 0.86 for the Madagascar region and a median crown age of 15.6 Ma (18.7 Ma under phytolith calibration). This "Madagascar shade clade" alone includes 17 of the strictly endemic C3 lineages. The secondlargest is the Hickeliinae subtribe of bamboos with 24 accessions, a relative area probability of 0.92 and median crown age of 6 Ma (7.3 Ma under phytolith calibration). The divergence of the only continental species, Hickelia africana, happened less than 2 Ma; in fact, sequences of a Hickelia specimen from Madagascar conservatively excluded were identical to H. africana. Further Madagascan origins were estimated for smaller clades in Chloridoideae (Acrachne-Sclerodactylon, Neostapfiella-Chloris humbertiana-Daknopholis, all C4), Micrairoideae (Isachne, C3), and Paniceae (Brachiaria-Yvesia, Setaria-Stenotaphrum, all C4). In the endemic C4 Panicum cinctum-luridum-voeltzkowii clade (Paniceae), a basal split is supported between taxa from Madagascar and from neighbouring Réunion, Europa, and Glorioso islands.

Discussion

C3 grasses: forest panicoid and bamboo radiations, recent migration, and possible relicts

Our results suggest that within the "Forest shade clade" (Panicoideae: Boivinellinae, [START_REF] Giussani | A molecular phylogeny of the grass subfamily Panicoideae (Poaceae) shows multiple origins of C4 photosynthesis[END_REF]), a large C3 lineage appears to have originated in Madagascar (Fig. II.5). This lineage comprises grasses found predominantly in shaded locations. Despite considerable intraspecific variation and often blurred species boundaries in genera such as Poecilostachys, it is clear that Madagascan taxa account for most of its diversity. Field experience (M.S. Vorontsova, pers. obs.) also suggests that a number of endemic species remain to be described. We specifically included additional non-Madagascan species in this group and believe we have a good representation of its worldwide diversity. The deep successive branching of Madagascan lineages strongly suggests the region as the clade's origin, which is supported by range evolution analysis. Besides regional endemics, this group also comprises species with a pantropical distribution such as Pseudechinolaena polystachya, Oplismenus burmanni, and O. compositus. From its likely origin in Madagascar, the group appears to have dispersed as far as Asia in a clade of Cyrtococcum, and the Neotropics in the case of Lasiacis. Stem and crown of the "Madagascar shade clade" are here estimated to the Early Miocene, although phytolith calibration also allows for a Late Oligocene origin.

The tropical woody bamboos of subtribe Hickeliinae are the second-largest clade with a Madagascan origin estimated here. This group originated in the Late Miocene, presumably via immigration from Southeast Asia, and diversified in the Late Miocene to Pliocene. One species, Hickelia africana, recently dispersed to East Africa. Judging by sequence similarity, it may moreover occur in Madagascar, too, which would imply an even more recent range expansion to the continent. We could not include any of the two endemic species of Cathariostachys, but they very likely also fall in the Hickeliinae [START_REF] Dransfield | Valiha and Cathariostachys, two new bamboo genera (Gramineae-Bambusoideae) from Madagascar[END_REF]. This bamboo subtribe and the "Madagascar shade clade" together probably account for more than half of the endemic C3 grass species in Madagascar, and diversification in these two clades may thus largely explain the higher proportion of endemic species in C3 compared to C4 grasses in Madagascar.

Humid forests are believed to exist in Madagascar since the Oligocene [START_REF] Wells | Some hypotheses on the Mesozoic and Cenozoic paleoenvironmental history of Madagascar. The natural history of Madagascar[END_REF]. The diversification of shade Paniceae and bamboos in the Madagascar region since the Miocene may have been favoured by factors such as the expansion of the Sambirano rainforests in the north [START_REF] Wells | Some hypotheses on the Mesozoic and Cenozoic paleoenvironmental history of Madagascar. The natural history of Madagascar[END_REF], Yoder & Nowak 2006) and the volcanic origin of the Comoros and Mascarenes [START_REF] Warren | Molecular phylogeography reveals island colonization history and diversification of western Indian Ocean sunbirds (Nectarinia: Nectariniidae)[END_REF]. It is consistent with the estimated ages of other forest plant lineages in the region such as the palm tribe Areceae [START_REF] Baker | Global biogeography and diversification of palms sheds light on the evolution of tropical lineages. II. Diversification history and origin of regional assemblages[END_REF], scaly tree ferns [START_REF] Janssen | Neoendemism in Madagascan scaly tree ferns results from recent, coincident diversification bursts[END_REF], or Canarium [START_REF] Federman | The biogeographic origin of a radiation of trees in Madagascar: implications for the assembly of a tropical forest biome[END_REF]. The extent of forests probably fluctuated with Pleistocene climatic cycles [START_REF] Burney | A chronology for late prehistoric Madagascar[END_REF]), which may have favoured recent allopatric speciation through fragmentation but also driven some species to peripheral humid refuges (e.g. Chasechloa egregia on Nosy Be island, [START_REF] Silva | Museomics resolve the systematics of an endangered grass lineage endemic to north-western Madagascar[END_REF]. The Hickeliinae bamboos have altitudinally patterned distributions [START_REF] Dransfield | Poaceae, Bambuseae, bamboos. The Natural History of Madagascar[END_REF], suggesting parapatric speciation as potential mechanism of diversification. With more data on the distribution of forest grasses, it would be possible to test models of allopatric versus parapatric speciation proposed for Madagascar (Wilmé et al. 2006, Vences et al. 2009).

In subfamily Oryzoideae, the forest endemics Maltebrunia leersioides (Oryzeae) and Humbertochloa bambusiuscula (Phyllorachideae) were both found to be sister to tropical African species, diverging from them in the Late Miocene to Quaternary. Humbertochloa fossils from the East African Miocene [START_REF] Jacobs | A Middle Miocene (12.2 my old) forest in the East African Rift Valley, Kenya[END_REF], and the deep divergence of the Phyllorachideae dated here to the Eocene to Oligocene suggest this lineage of only three or four species (Soreng et al. 2015) may have originated in a hot and humid environment of continental Africa and dispersed to Madagascan forests only recently when forests expanded there. Another small, predominantly forest understorey clade was found in the temperate bamboos (Arundinarieae: Arundinaria p.p.), grouping with the South African Oldeania alpina and diverging in the Pliocene to Quaternary; support for this group however is only moderate, as in most of this young bamboo tribe. Endemic C3 lineages of high altitudes in the Pooideae (Agrostis, Anthoxanthum, Festuca, and Poa; less clear in Brachypodium) appear to have immigrated from Eurasia in the Pliocene or more recently. They clearly form part of a "pantemperate element" in the African mountain flora [START_REF] Gehrke | The scramble for Africa: pan-temperate elements on the African high mountains[END_REF][START_REF] Minaya | Contrasting dispersal histories of broad-and fineleaved temperate Loliinae grasses: range expansion, founder events, and the roles of distance and barriers[END_REF][START_REF] Tusiime | Sweet vernal grasses (Anthoxanthum) colonized African mountains along two fronts in the Late Pliocene, followed by secondary contact, polyploidization and local extinction in the Pleistocene[END_REF]. Further endemic mountain C3 grasses in Sartidia (Aristidoideae), Pentameris and Merxmuellera (both Danthonioideae) appear to have their origin in Southern Africa, which is consistent with previous hypotheses [START_REF] Besnard | From museums to genomics: old herbarium specimens shed light on a C3 to C4 transition[END_REF], for Sartidia, Linder et al. 2014, for Danthonioideae). Older endemic C3 lineages in Madagascar include Styppeiochloa (Arundinoideae), with further species awaiting description in addition to S. hitchcockii (J. Teisher, pers. comm.). The two accessions from Madagascar included here are highly divergent (~5-15 Ma), and the genus diverged in the Miocene to possibly Late Eocene. The lineage may have been more widespread in sunexposed habitats before C4 grasses overtook dominance. It now only persists on higher plateaus, where alternative adaptations to dry habitats such as strong desiccation tolerance may explain its frequent co-occurrence with C4 grasses (G. Besnard, pers. obs.). Lecomtella madagascariensis (Panicoideae) is another possible relict of uncertain phylogenetic postion (Besnard et al. 2013). We estimated its divergence from Andropogoneae-Arundinelleae and the Asian Jansenella griffithiana at least to the Early Miocene. A recent phylogenomic study (Burke et al. 2016b) placed it at the base of the core Panicoideae, suggesting it may be even older. Lecomtella is very likely the oldest endemic grass lineage in Madagascar. It was possibly more widespread at lower altitudes during the cooler Oligocene and now persists only on the summit of the Andringitra massif (Besnard et al. 2013).

C4 grasses: Miocene to Pliocene origins and two possible relicts

We show here that C4 grasses count nearly twice as many lineage origins in Madagascar compared to C3 grasses (44 versus 25 recovered) although they have less endemic species (100 versus 120). This suggests that while in situ radiations produced larger endemic clades in C3 grasses, there were more independent colonisations of C4 grasses. Median stem ages of most endemic C4 lineages, and crown ages of endemic clades in the Aristidoideae (Aristida rufescens-similis), Chloridoideae and Panicoideae, are younger than 8 Ma (some only marginally so under phytolith calibration) and thus compatible with the onset of the global Miocene grassland expansion (Edwards et al. 2010). Many colonisations appear to have occurred only in the Quaternary. In contrast, some lineages (including the Aristida rufescenssimilis complex, a major component of present central plateau grasslands) may have been present before 8 Ma. Divergences of the isolated Aristida ambongensis and Eragrostis chabouisii were tentatively estimated to the Early to Mid Miocene. These potentially oldest endemic C4 lineages in Madagascar are only known from the dry west and sub-arid southwest, respectively, and may be remnants from a once more widespread dry bush vegetation [START_REF] Wells | Some hypotheses on the Mesozoic and Cenozoic paleoenvironmental history of Madagascar. The natural history of Madagascar[END_REF].

Taking crown ages of endemic C4 clades under external calibration as a minimum estimate, our results suggests that open-canopy habitats suitable for diversification of C4 taxa existed in Madagascar at least by the Pliocene. They thus support the view that grasslands in Madagascar form part of the global expansion of C4 grassy biomes (Bond et al. 2008). They could even be older if one considers the uncertainty about the age of Poaceae (see below). We stress, however, that this gives no indication of the area these may once have occupied. Primitive C4 grassy biomes in Madagascar may have occurred in small patches, in a mosaic with other vegetation (Burney 1987[START_REF] Lowry | The classification of natural and anthropogenic vegetation in Madagascar. Natural change and human impact in Madagascar[END_REF][START_REF] Godfrey | Madagascar's ephemeral palaeo-grazer guild: who ate the ancient C4 grasses[END_REF], or may have occupied more extensive areas. Moreover, their extent probably fluctuated with Quaternary climatic variations [START_REF] Burney | A chronology for late prehistoric Madagascar[END_REF]). Some may have resembled today's tapia (Uapaca bojeri) woodlands, where C3 and C4 grasses are frequently found in close proximity. As shown here, a number of endemic C4 grasses colonised Madagascar only in the Quaternary, underlining the fact that species assemblages in open biomes continued evolving until very recently. C4 photosynthesis, although generally an adaptation to open and warm habitats, covers a large ecological spectrum (Christin & Osborne 2014), and C4 grassland communities in South Africa have been shown to cluster phylogenetically depending on humidity, fire regime, and grazer disturbance [START_REF] Visser | Environmental factors determining the phylogenetic structure of C4 grass communities[END_REF]. In Madagascar, Andropogoneae and Chloridoideae also tend to dominate in more mesic versus more dry habitats, respectively (Bond et al. 2008). The assembly histories of such different grassland types may not have been the same. The challenge therefore lies in characterising the different types of old-growth grasslands and savannahs in Madagascar and distinguishing them from secondary vegetation. More research on the distribution, regional endemism, community structure, and possibly phylogeographic patterning of grasses (e.

Madagascar's extant grass flora: Neogene diversification and frequent dispersals

In this study, we aimed to understand the assembly of the grass flora in the Madagascar region, and to compare the diversification of C3 and C4 grasses. Studies like ours are subject to some limitations, in particular due to taxon sampling and the age calibration used.

We attempted to include as many taxa as possible, for Madagascar as well as other areas. The overall proportion of species sampled per clade ranged between roughly 10% (Andropogoneae-Arundinelleae) and 65% (Brachypodieae), while we have a better sampling of the Madagascan grass flora and its endemics (73% and 65%, respectively). We thus assume to have a good minimum estimate of the endemic lineages and lineage origins in Madagascar, although the true numbers may be higher. Ancestral range estimates are more likely to be affected by species sampling. They are consistent overall with current-day distribution patterns, with the notable exceptions of India and the Neotropics. It is possible that we underestimated India's historical links with Madagascar, given also the known affinities of the Indian and Madagascan floras in general [START_REF] Schatz | Malagasy/Indo-Australo-Malesian phytogeographic connections[END_REF], Buerki et al. 2013). In turn, the Neotropical grass flora is relatively well studied, which may have biased upwards our estimates for its historical contribution. Finally, the lineage-through-time curves (Fig. II.3) inferred for the Madagascar region are valid within the limits of our species sampling and give only minimum estimates of past diversity.

The age of Poaceae is subject of an ongoing debate, owing in particular to the uncertain value of phytolith fossils (Christin et al. 2014). The recent inclusion of an old macrofossil, presumably a grass spikelet [START_REF] Poinar | One hundred million year old ergot: psychotropic compounds in the Cretaceous?[END_REF], added to the discussion and led to conspicuously old Poaceae age estimates (Burke et al. 2016a). Here, rather than subjectively choosing one set of fossils, we opted to use the two alternative hypotheses produced by Christin et al. (2014) as secondary calibrations, and test their implications for the Madagascan grass flora. We show that ages under both calibrations support the notion of a largely Neogene origin of Madagascan grasses. They approach each other for recent divergences, probably because they are effectively constrained where lineage sampling is denser. Much of the uncertainty in Poaceae concerns deeper divergences, which do not directly concern Madagascan lineages. However, we acknowledge that if the taxonomic placement of phytoliths and ancient macrofossils are confirmed and compatible with external angiosperm constraints, ages of grasses in Madagascar may lie nearer the upper end of our estimated confidence intervals. We expect that the precise branching order of the PACMAD subfamilies (see [START_REF] Cotton | Resolving deep relationships of PACMAD grasses: a phylogenomic approach[END_REF] has little effect on our age estimates, as the branches between them are very short [START_REF] Cotton | Resolving deep relationships of PACMAD grasses: a phylogenomic approach[END_REF][START_REF] Gpwg Ii | New grass phylogeny resolves deep evolutionary relationships and discovers C4 origins[END_REF].

The 69 lineages estimated here to have their origin in the Madagascar region suggest recurrent dispersals to Madagascar and its outlying islands. Dispersal appears to be constrained by distance, demonstrated by the very strong support for range evolution models incorporating a negative distance scaling parameter x in 9 of 11 phylogenies analysed. Linder et al. (2013) and [START_REF] Minaya | Contrasting dispersal histories of broad-and fineleaved temperate Loliinae grasses: range expansion, founder events, and the roles of distance and barriers[END_REF] also found a negative correlation between dispersal rate and distance in the Danthonioideae and Loliinae (subfamily Pooideae) lineages of grasses, respectively. It appears that, despite often large ranges, dispersal limitation has shaped the distribution of the grass family. Few studies have so far included the x parameter, and we expect that it will provide a good fit for many plant phylogenies. The inference of Tropical and Southern Africa as areas with strongest historical and modern links with Madagascar is in line with patterns of taxonomic similarity in many plants groups (Buerki et al. 2013).

A final remark we would like to make concerns the role of extinction. This parameter is not easily tractable in historical biogeography, and our inferences are valid only for the lineage diversity we sampled, i.e. the branches leading to extant species. The island of Madagascar underwent significant environmental change since its split from Gondwana [START_REF] Wells | Some hypotheses on the Mesozoic and Cenozoic paleoenvironmental history of Madagascar. The natural history of Madagascar[END_REF]. Species on long branches such as Eragrostis chabousii, only found in the south-western spiny bush, and Lecomtella madagascariensis from the high Andringitra, may be the only remnants from lineages that once were more diverse. We cannot exclude the possibility that an older, quite different assemblage of grasses was present on Madagascar before the extant grass flora emerged. If there was expansion of open habitats in Madagascar during the global Miocene grassland expansion, it is indeed likely that this was accompanied by significant lineage turnover.

To conclude, we infer that the extant grass flora of that Madagascan region diversified from the Miocene onwards, but there remains some possibility that lineages are older than we estimated. A few phylogenetically isolated lineages may be remnants from ancient biomes that retracted with environmental change, and extinction is likely to have occurred. Biogeographical links are strongest with Tropical and Southern Africa. C3 grasses include two likely in situ radiations of bamboos and forest Paniceae that account largely for their higher proportion of endemics. There were twice as many immigration events in C4 grasses than in C3 grasses. C4 grasses have been present and diversified in Madagascar since at least the Pliocene, supporting the idea that there are old-growth C4 grassy biomes on the island.

4 Chapter III: Phylogenomics and biogeography of the core Panicoideae 1

Abstract

Within the grass family (Poaceae), the subfamily Panicoideae includes diverse clades that dominate tropical C 4 grasslands, such as Andropogoneae, but also some C3 species with uncertain positions. These species, notably in the two genera Chandrasekharania and Jansenella, are potentially important for our understanding of C3-C4 transitions and the origins of C4 grasslands. We attempted to establish their positions in the grass phylogeny using phylogenomic methods. We assembled full chloroplast genomes, the nuclear genes phyB, the nuclear nadpme and ppc gene families and as the ITS region from shotgun sequencing data. Phylogenies were reconstructed and divergence times estimated from chloroplast genomes. We analysed specific C4-related aminoacid sites in the ppc and rbcL genes. Distribution patterns were compared for the major core Panicoideae lineages. Results confirm Gynerium as sister to the remaining core Panicoideae, while the branching order of Lecomtella and Paniceae remains unclear. A polyploid origin was inferred for Gynerium and Jansenella neglecta, and potentially Lecomtella. The three species of Chandrasekharania and Jansenella are sister to the large C4 clade Andropogoneae-Arundinelleae and have ppc and rbcL features typical of C3 plants. The lineage, as Andropogoneae-Arundinelleae, has its centre of diversity and endemism in India. The position of the C3 clade Jansenella-Chandrasekharania sister to Andropogoneae-Arundinelleae suggests that the transition to C4 photosynthesis occurred on the Indian subcontinent, in the Early Miocene. The Jansenella-Chandrasekharania clade will be useful for comparative studies on the evolution of C4 photosynthesis.

Introduction

Within the cosmopolitan grass familiy (Poaceae), Panicoideae is one of the largest subfamilies, with roughly 3,300 species (Soreng et al. 2015, Kellogg 2015). This lineage is mainly distributed in the tropics, where its members are among the dominant plants in open biomes [START_REF] Osborne | Atmosphere, ecology and evolution: what drove the Miocene expansion of C4 grasslands?[END_REF]. Tropical grassy biomes cover around 20% of the global land surface and have received increasing attention due to their importance for biodiversity and the global carbon cycle, particularly in a context of global change (Parr et al. 2014, Bond 2016, Lehmann & Parr 2016). The ecology of these biomes is tightly linked to the evolution of C4 photosynthesis, which is an adaptation to the high photorespiration costs in warm and open habitats and plays a role in the productivity that fuels the regular fires [START_REF] Osborne | Atmosphere, ecology and evolution: what drove the Miocene expansion of C4 grasslands?[END_REF]). In the Miocene, between 3 and 10 million years ago (Ma), C4 grasslands expanded globally, but timing and pace were not the same between different regions and continents (Edwards et al. 2010, Strömberg 2011). Multiple clades of grasses independently evolved the C4 pathway, of which most are concentrated in subfamily Panicoideae, which alone counts 22-24 C4 origins (Kellogg 2015).

1 The results of this chapter have not been published elsewhere when this dissertation was completed. Molecular phylogenetic analyses of the Panicoideae have identified a "core" clade, including notably the large tribes Paniceae, Paspaleae, Andropogoneae, and Arundinelleae (GPWG II 2012, Burke et al. 2016). The latter two (also classified as a single tribe Andropogoneae, Kellogg 2015) are sister to each other and composed of C4 species only, suggesting a single common C4 origin. Paniceae and Paspaleae, on the contrary, each include several origins of C4 photosynthesis (GPWG II 2012). These C3-to-C4 transitions led to some large radiations, albeit with different geographic distributions: Paniceae is largely pantropical, while most genera of Paspaleae are neotropical, and Andropogoneae-Arundinelleae are dominated by Asian members [START_REF] Soreng | A worldwide phylogenetic classification of the Poaceae (Gramineae) II: An update and a comparison of two 2015 classifications[END_REF]. Andropogoneae, in particular, are the dominant grasses in all Asian savannah types (Ratnam et al. 2016). Resolving the origins and diversification of these C4 groups, in their respective temporal and geographical settings, is necessary to understand both the common features and the particularities of modern tropical grassy biomes.

The C4 species in Panicoideae have been intensively studied, particularly those of economic interest such as maize and sorghum, whose genomes have been sequenced. However, to understand the origin of C4 clades, it is necessary to take into account their C3 relatives, too (Christin et al. 2009a). Several of these are species-poor lineages and have often been overlooked in phylogenetic analyses. The monotypic genus Gynerium from tropical America is believed to be sister to the rest of the core panicoids based on analysis of the rbcL, ndhF, and matK plastid genes [START_REF] Barker | Polyphyly of Arundinoideae (Poaceae): Evidence from rbcL sequence data[END_REF][START_REF] Gpwg Ii | New grass phylogeny resolves deep evolutionary relationships and discovers C4 origins[END_REF]. Another monotypic C3 genus, Lecomtella from the Andringitra range in Madagascar, has been ambiguously placed so far. Besnard et al. (2013) showed that it is a distinct lineage in the core Panicoideae but with unclear relationship to the other tribes, depending on whether selected plastid markers, whole plastomes, or nuclear data were used. A recent whole-plastome analysis placed it as sister to a clade of Paniceae, Paspaleae and Andropogoneae-Arundinelleae (Burke et al. 2016).

The panicoid genera Jansenella and Chandrasekharania, both assumed to be C3 (Osborne et al. 2014[START_REF] Watson | Grass genera of the world. Available at: deltaintkey[END_REF], have been enigmatic in terms of phylogenetic affinities. They have been included in Arundinelleae [START_REF] Bor | Notes on Asiatic grasses: XXIII. Jansenella Bor, a new genus of Indian grasses[END_REF][START_REF] Sánchez-Ken | Phylogeny and a new tribal classification of the Panicoideae s.l. (Poaceae) based on plastid and nuclear sequence data and structural data[END_REF], referred tentatively to the otherwise C4 tribe Tristachyideae (Kellogg 2015), considered incertae sedis in Panicoideae (Soreng et al. 2015), and again included in Arundinelleae [START_REF] Soreng | A worldwide phylogenetic classification of the Poaceae (Gramineae) II: An update and a comparison of two 2015 classifications[END_REF]. Of the three known species, Jansenella griffithiana was described over 170 years ago [START_REF] Müller | Manipulus Graminearum novarum[END_REF]) and has the widest known distribution range, from Sri Lanka over India to Thailand [START_REF] Bor | Notes on Asiatic grasses: XXIII. Jansenella Bor, a new genus of Indian grasses[END_REF][START_REF] Teerawatnanon | Jansenella griffithiana (Müll. Hal.) Bor (Gramineae/Poaceae): a new record for Thailand, and notes on its typification[END_REF]. Jansenella neglecta and the single species Chandrasekharania keralensis were described more recently and are both known only from southern India [START_REF] Nair | Chandrasekharania: A new genus of Poaceae from Kerala, India[END_REF][START_REF] Yadav | On the identity of Jansenella griffithiana (Poaceae) with a new species from Western Ghats, India[END_REF]. Jansenella griffithiana is the only species so far included in a molecular phylogenetic study, which placed it sister to Andropogoneae-Arundinellae based on ndhF, matK and rbcL (see chapter II). This position is interesting for two reasons. First, a C3 sister lineage of Andropogoneae-Arundinelleae would allow direct comparisons for studies on the origin of the photosynthetic pathway in one of the largest known C4 clades [START_REF] Besnard | Evolutionary genomics of C4 photosynthesis in grasses requires a large species sampling[END_REF]. Second, the high diversity of this C4 clade in south and south-east Asia [START_REF] Hartley | Studies on the origin, evolution and distribution of the Gramineae. I. The tribe Andropogoneae[END_REF], combined with the known distribution of Chandrasekharania and Jansenella, would suggest an origin of Andropogoneae-Arundinelleae on the Indian subcontinent.

Here, we assembled complete chloroplast genomes (hereafter plastomes) and nuclear genes for all three species known in Jansenella and Chandrasekharania. We placed them within a phylogeny of the Panicoideae to test their sister relationship with Andropogoneae-Arundinelleae and checked whether two phyotosynthesis-related genes had a C4 signature. Further, we re-investigate the positions of the two isolated, monotypic tropical C3 genera Lecomtella and Gynerium. Finally, we estimate divergence times and discuss the biogeographical implications of the position of these tropical C3 taxa.

Materials and Methods

Species sampling

We analysed one herbarium specimen for each of the three known species in Chandrasekharania and Jansenella, including isotypes of Ch. keralensis and J. neglecta. We also sequenced further specimens from major tribes of Panicoideae: Andropogoneae (Glyphochloa forficulata and Lasiurus scindicus), Arundinelleae (Arundinella nepalensis), Gynerieae (Gynerium sagittatum), Paspaleae (Reynaudia filiformis, presumably the earliestdiverging member of the tribe; GPWG II 2012), Tristachyideae (Danthoniopsis stocksii) and Paniceae (Digitaria glauca, Melinis minutiflora). Further sequences were obtained from GenBank: we generated a dataset of full chloroplast genomes (hereafter plastomes) focused on the core Panicoideae for which a good amount of sequences has been produced recently (Burke et al. 2016[START_REF] Arthan | Phylogenomics of Andropogoneae (Panicoideae: Poaceae) of mainland Southeast Asia[END_REF], Piot et al. 2017), with one further representative plastome added for each of the other panicoid tribes (except Cyperochloeae and Steyermarkochloeae, both unavailable) and Poaceae subfamilies. Nuclear sequences were also assembled from shotgun data (see below), and we supplemented these with homologous Poaceae sequences which were retrieved directly and through BLAST searches from GenBank. All plastome sequences used are listed with voucher names and GenBank accessions in Table A

-III.1 in annex A-III.
DNA extraction, sequencing, and sequence assembly DNA was extracted from very small amounts of herbarium material, mostly leaves, or one single seed in the case of Ch. keralensis, using the BioSprint 15 DNA Plant Kit (Qiagen Inc.). DNA was then sequenced on a HiSeq 3000 machine at Genotoul, Castanet-Tolosan, France, or on a HiSeq 2000 machine at Genoscope, Evry, France, applying a low-coverage, genomeskimming strategy.

The 100 or 150 bp paired-end reads obtained were first used to assemble full plastomes. We used the Org.Asm organelle assembler v. 1.0 (http://pythonhosted.org/ORG.asm) with coding sequences of Axonopus fissifolius (KU291491.1, Paspaleae) as seeds for initiating contig assembly. Final assemblies were checked by mapping reads on the obtained circular sequence in Geneious v. 9.0.5 (Biomatters Ltd., Auckland). Low-copy nuclear genes were assembled manually for A. nepalensis, Ch. keralensis, Gl. forficulata, Gy. sagittatum, J. griffithiana, J. neglecta, La. scindicus, Le. madagascariensis and R. filiformis, following the method described by [START_REF] Besnard | From museums to genomics: old herbarium specimens shed light on a C3 to C4 transition[END_REF]. We focused on genes frequently employed in grass phylogenetics and with a large species sampling available: phyB (phytochrome B) and the gene families nadpme (coding for NADP-malic enzyme) and ppc (coding for phosphoenolpyruvate carboxylase). The latter two include genes that are implicated in the C4 photosynthetic pathway. While for some accessions assembly was straightforward, only incomplete sequences could be assembled for others. Some accessions were polymorphic at the studied loci (see Results). We were able to separate the different copies in some cases by phasing the reads, but in other cases we could only separate short stretches (in general exons) and were not able to match fragments of each copy throughout the sequence. The complete nuclear ribosomal cluster, including the internal transcribed spacer (ITS) region, was also assembled for Ch. keralensis, J. grifftihiana, and J. neglecta.

Phylogenetics and divergence time estimation

The 88 full plastomes were aligned with MAFFT v. 7.2 (Katoh & Standley 2013) with default parameters, after removing one of the inverted repeat regions. A visual check of coding sequence (CDS) translations revealed no obvious alignment errors. We then estimated phylogenies on (i) the whole alignment, (ii) only alignment columns without any gaps (as done by Burke et al. 2016), and (iii) only CDS regions. RAxML v. 8.2.4 (Stamatakis 2014) was used for Maximum Likelihood (ML) estimation, applying a GTR substitution model and the CAT model of site heterogeneity with 25 rate categories and specifying Anomochloa marantoidea as outgroup. One thousand rapid bootstrap searches were run to assess node support, followed by a thorough ML search (-f a option of RAxML). Sequences of phyB (91, part of exon 1), ITS (210) and the nadpme and ppc families (116 and 145, exons 2-17 and 2-9, respectively) were each aligned using MAFFT, using the E-INS-i algorithm for the indelrich ITS. RAxML was then used to estimate ML phylogenies, with parameters as stated above but using a Gamma model of rate heterogeneity.

Divergence time estimation using BEAST2 was performed on the CDS-only plastome dataset. We specified a normal prior with a mean of 54.9 Ma and a standard deviation of 5.8 Ma for the BOP-PACMAD split, based on a previous Poaceae-wide study using external angiosperm calibration (Christin et al. 2014). We applied a GTR substitution model with four rate categories, a Yule tree prior and a log-normal relaxed clock. Two Markov Chain Monte Carlo runs with 20 million generations were performed, sampling parameter estimates and trees every 10,000 generations. The log files were examined in Tracer v. 1.6 (http://tree.bio.ed.ac.uk/software/tracer/) to ensure adequate mixing and Effective Sample Sizes of >200 for all parameters (except rate variation among branches which is difficult to estimate, P.-A. Christin, pers. comm.). A Maximum Clade Credibility Tree was computed from the combined chains, discarding a 10% burn-in each, using TreeAnnotator from the BEAST2 package. Both RAxML and BEAST2 analyses were performed on the computing cluster of the Évolution & Diversité Biologique laboratory, Toulouse.

Codon changes in ppc-B2 and rbcL

We compared amino-acid sequences of the nuclear gene ppc-B2 (coding for phosphoenolpyruvate carboxylase) and the chloroplast gene rbcL (coding for the large subunit of Rubisco) between accessions in our alignments. Both genes have been found to be under C4-related positive selection in grasses, with 12 particular codons found in both genes that underwent convergent adaptive changes [START_REF] Salamin | C4 photosynthesis evolved in grasses via parallel adaptive genetic changes[END_REF], Piot et al. 2017). We were interested in the amino-acid residues of Chandrasekharania and Jansenella at these sites, particularly with respect to their putative C4 sister clade Andropogoneae-Arundinelleae.

Distribution and endemism or core Panicoideae lineages

We generated maps of global distribution and endemism for the lineages of the core Panicoideae. Species-level distribution data for TDWG level-3 botanical regions, which broadly correspond to countries or states, were obtained from the World Catalogue of Selected Plant Families (Clayton et al. 2016). Grass genera were assigned to tribes according to the most recent classification [START_REF] Soreng | A worldwide phylogenetic classification of the Poaceae (Gramineae) II: An update and a comparison of two 2015 classifications[END_REF]. We retrieved the total number of species and the number of endemics per TDWG level 3 botanical region for the large tribes Andropogoneae, Arundinelleae, Paniceae, and Paspaleae. Location records marked as doubtful were not considered. Note that the regions have different area, but correcting for this is not simple because very small regions would distort the figures. Botanical region shapefiles were obtained from the Royal Botanic Gardens, Kew (https://www.kew.org/ gis/tdwg/index.html, accessed on 10 August 2017). The R package rgdal [START_REF] Bivand | rgdal: Bindings for the Geospatial Data Abstraction Library[END_REF]) was used to read shapefiles and plot distribution and endemism data. For Gy. sagittatum and J. griffithiana, we reported the level-3 regions they occur in. For the range-restricted Ch. keralensis, J. neglecta and Le. madagascariensis, we referred to the relevant literature [START_REF] Bor | Notes on Asiatic grasses: XXIII. Jansenella Bor, a new genus of Indian grasses[END_REF][START_REF] Nair | Chandrasekharania: A new genus of Poaceae from Kerala, India[END_REF][START_REF] Teerawatnanon | Jansenella griffithiana (Müll. Hal.) Bor (Gramineae/Poaceae): a new record for Thailand, and notes on its typification[END_REF][START_REF] Yadav | On the identity of Jansenella griffithiana (Poaceae) with a new species from Western Ghats, India[END_REF], Besnard et al. 2013[START_REF] Ramachandran | On the occurrence of Jansenella neglecta Yadhav et al., and Polypogon nilgiricus Kabeeer & V.J.Nair (Poaceae) from the Nilgiris, Tamil Nadu[END_REF].

Results

Sequence assembly

We generated new complete plastome sequences for 11 species, including Chandrasekharania keralensis and the two known species of Jansenella, using genomeskimming data from herbarium material. We also assembled low-copy nuclear genes, phyB and the nadpme and ppc gene families, for nine of these taxa, with varying success, and complete nuclear ribosomal clusters for Ch. keralensis, J. griffithiana and J. neglecta. Jansenella griffithiana and Ch. keralensis appeared to be homozygous at all sites, and sequences complete with introns were assembled for all genes. Mostly complete sequences were also obtained for Lasurus scindicus, Lecomtella madagascariensis and Reynaudia filiformis. Assembly was more challenging in other cases due to low read coverage and/or polymorphic sites. The accessions of Jansenella neglecta and Gynerium sagittatum consistently revealed two copies of each gene. In J. neglecta, one copy was always very similar to J. griffithiana, which allowed to consistently separate them. In contrast, while copies could be separated by phasing the reads for each exon in Gy. sagittatum, it was impossible to track them through introns. In Le. madagascariensis, we found two copies for nadpme-II and ppc-aL1a but not for the other genes. The ppc-B1 gene appeared to be pseudogenized in Le. madagascariensis and Gy. sagittatum, with long deletions and/or frameshift mutations. In R. filiformis, ppc-B2 was potentially duplicated, with two variants of equal proportion in the first portion of the gene, and we assembled a consensus sequence. The ppc-aL1b gene could not be detected in J. griffithiana, despite good sequence coverage. Finally, three copies of nadpme-IV were detected in A. nepalensis. We estimated phylogenetic relationships through ML on three different subsets of a complete plastome alignment. Relationships were mostly congruent between the three topologies, which all had high bootstrap support for most nodes (i.e. >90; summarised in Fig. PACMAD subfamilies also depends on subset choice, with either Aristidoideae or Panicoideae placed as sister to the others, with varying support.

Plastome phylogeny and divergence times

The relationships found with Bayesian divergence time estimation on the CDS subset were congruent with the ML analysis (Fig. III.1). Table III.1 lists age estimates for selected nodes with 95% high posterior density (HPD) intervals for the two calibrations, and Fig. 1 shows median ages and HPD intervals for all nodes.

Nuclear gene phylogenies

The topologies estimated with nuclear sequences are partially congruent with those estimated with plastomes. The phyB tree confirmed Chandrasekharania-Jansenella as sister clade of Andropogoneae-Arundinelleae (Fig. The topologies found for the nadpme and ppc gene families (Figs III.3, A-III.4-5) confirmed the relationships among genes found in previous studies [START_REF] Salamin | C4 photosynthesis evolved in grasses via parallel adaptive genetic changes[END_REF], Christin et al. 2009b). Within the clade of almost every individual gene, Jansenella-Chandrasekharania was supported as sister group of Andropogoneae-Arundinelleae. Sequences of ppc-B2 placed the two genera in a paraphyletic grade of C3 species (plus Stipagrostis, which recruited ppc-aL1b instead for the C4 function, Christin & Besnard 2009) basal to a C4 cluster. In the clade of ppc-B1, absent from Andropogoneae-Arundinelleae, they were sister to a poorly supported clade of Paniceae, Paspaleae, and Gy. sagittatum. The nadpme and ppc copies of Lecomtella were mostly poorly supported as diverging before or after Paniceae, or as sister to either Paniceae or Paspaleae. The two copies of ppc-aL1a in Lecomtella were paraphyletic at the base of the core Panicoideae (Gy. sagittatum not being included). For Gy. sagittatum, only nadpme-IV could be included of the nadpme sequences, the others yielding only short exons. The two nadpme-IV copies were paraphyletic at the base of the core Panicoideae, one clustering with Orthoclada laxa (tribe Zeugiteae). Sequences of ppc-aL1b, ppc-B1 and ppc-aR placed Gy. sagittatum sister to Paniceae, with poor support, while ppc-aL2 supported it as sister to the rest of core Panicoideae.

Codon changes in ppc-B2 and rbcL

Amino-acid translations at sites previously shown to be under C4-related selection in ppc-B2 and rbcL are more similar to C3 grasses in Chandrasekharania and Jansenella (Table III.2). Most importantly, site 780 of ppc-B2 which is a serine (S) in most C4 plants is an alanine (A) in all three species, as in all C3 grasses and Stipagrostis. The same site also translates to alanine in all other ppc paralogs for the three species (not shown). Residues at other selected sites of ppc-B2 also place them with C3 groups and distinguish them from Andropogoneae-Arundinelleae. In rbcL, Chandrasekharania and Jansenella are likewise more similar to C3 than to C4 groups, with the exception of a lysine (K) at site 471, which is also the most frequent amino acid at this site in Andropogoneae but an alanine (A) in Arundinelleae. Note that in La. scindicus, rbcL encodes a protein with six additional amino acids at the C-terminal part, which were absent in all other Andropogoneae.

Distribution and endemism

Maps of distribution and endemism show quite different biogeographic patterns for the lineages of the core Panicoideae, all most diverse in tropical areas (Fig. III.4). While G. sagittatum is widespread in the Neotropics, Le. madagascariensis is confined to a single mountain range in southern Madagascar. The largest tribe, Paniceae, is pantropical but has its centres of diversity and endemism in tropical Africa and especially Madagascar. This pattern remains when the polyphyletic Panicum -accounting for almost one third of Paniceae, with some probably belonging to Paspaleae (Kellog 2015) -is excluded (not shown). Paspaleae is largely neotropical, with diversity and endemism peaking in west-central Brazil. In Jansenella-Chandrasekharania, J. griffithiana is known from India, Sri Lanka, Myanmar and Thailand, while the other two species are restricted to the Western Ghats of southwest India, with only one record known of Ch. keralensis. Andropogoneae and Arundinelleae are both widespread but have their centres of diversity and endemism in India.

Table III.2. Amino acid residues at sites in the chloroplast gene rbcL and the nuclear gene ppc-B2 previously shown to be under C4-related positive selection [START_REF] Salamin | C4 photosynthesis evolved in grasses via parallel adaptive genetic changes[END_REF], Piot et al. 2017). Shown are the dominant residues for selected grass clades (Jansenella-Chandrasekharania highlighted), with minor residues in brackets. Asterisks indicate that values could be determined for only one of the two ppc-B2 copies in Jansenella neglecta. Note that C3 and C4 clades in Paniceae and Paspaleae were each grouped together. Codon positions refer to NC_001666.2 for rbcL and CAA33317.1 for ppc-B2 (both Zea mays).

V P A S H M S D K A M L (I) (V/S) (I) (Q/E/V) (T) (Q/V) (I/V) Arundinelleae (C4) V P A/S A/S H I/M A/S D/E A P V I Jansenella- V P S A H M A E K P V I Chandrasekharania (C3) Paspaleae (C3) V P S A H M A E A P V I Paspaleae (C4) I (T) P S (S) S H I S (D) D (K) D/K P V I Paniceae (C3) (V) V P/T S A H (M) M A (E) E (E) A P V I Paniceae (C4) I P A/S A H M S D E P V I (V) (V/I/T) (S) (Y) (I) (A) (E) (A/K/Q) (A) (M) (V/L) Lecomtella (C3) V P S A H M A E A P V I Gynerium (C3) V P S A H M A E A P V I ppc-B2
P P S E A L A S V K (R) Arundinelleae I A P R S E A F A S F K Jansenella- Chandrasekharania L T* A R* A A V M S* A* F* R* Paspaleae (C3) V T A R A A V M S A F R Paspaleae (C4) I A P P A E V M S S F K Paniceae (C3) L T A R A A V M S A F R Paniceae (C4) I C P P S E A M A S V (F) K Lecomtella (C3) L T A R A A V M ? A ? R Chasmanthieae (C3) I T A R A A V M S A F R Chloridoideae (C4) V C P P S E A F A S V K Arundinoideae (C3) L T A R A A V M S A F R Aristidoideae: Aristida (C4) I T P P S E Q F S S I K Aristidoideae: Stipagrostis (C4) L T A R A A V M S A F R Pooideae (C3) L T A R A A V M S A F R

Discussion

Phylogeny of the core Panicoideae and the roles of polyploidy and duplication

We here report a phylogenomic analysis of the core Panicoideae including for the first time full plastomes of the phylogenetically isolated Gynerium sagittatum, the enigmatic genera Chandrasekharania and Jansenella (see next section), the earliest-branching Paspaleae species Reynaudia filiformis, and Lasiurus scindicus which we found be the earliestbranching Andropogoneae species. We supplemented the plastome analysis with data from nuclear genes. Overall, the results confirm previously found relationships in the core Panicoideae (GPWG II 2012, Burke et al. 2016) but still leave some uncertainty on the branching order or Lecomtella and Paniceae and the monophyly of Arundinelleae.

Gynerium sagittatum is confirmed as earliest-branching core panicoid by the plastome analysis, diverging in the Early Oligocene (Fig. III.1). Sequence assembly from shotgun data consistently revealed two divergent nuclear gene copies. While we could not include sufficiently long sequences of all nadpme and ppc paralogs in our phylogenies, the topologies of phyB (Fig. III.2) and nadpme-IV (Fig. III.3) revealed paraphyly of the two copies at the base of the core Panicoideae, suggesting allopolyploidy, though poorly supported in the case of phyB. Indeed, 44 chromosomes were determined for this species [START_REF] Pohl | Chromosome numbers of Costa Rican grasses[END_REF] and interpreted as a basic number of x = 11 [START_REF] Hilu | Phylogenetics and chromosomal evolution in the Poaceae (grasses)[END_REF]). Gynerium sagittatum is widespread in the Neotropics (Fig. III.4), but it is unknown whether all populations are polyploid. One of the two variants of nadpme-IV in Gy. sagittatum was placed with Orthoclada laxa (tribe Zeugiteae). That species is equally widespread in the Neotropics (Clayton et al. 2016), so a horizontal transfer of that gene could have occurred in an ancestor of the two species.

Lecomtella madagascariensis was previously placed in various positions in the core Panicoideae depending on the data analysed (Besnard et al. 2013, Burke et al. 2016). Here, we were still not able to fully resolve its position, showing that it depends on the choice of characters in the plastome alignment and the inclusion of Gy. sagittatum (Fig. A-III.1). Its divergence occurred either before or after Paniceae. The branches between these two lineages are extremely short, which explains the difficulties of resolving them. In any case, the stem of Le. madagascariensis would fall in the Early Oligocene (Fig. III.1, Table III.1), confirming it as the likely oldest endemic grass lineage in Madagascar (see chapter II). We also observed two paraphyletic copies of ppc-aL1a in Le. madagascariensis (Fig. III.3), suggesting an ancient duplication event or an allopolyploid origin of the lineage which has since been obscured by chromosomal rearrangements and homogenisation. The chromosome number of this species is unknown (Besnard et al. 2013).

Jansenella-Chandrasekharania, a C3 sister group of Andropogoneae-Arundinelleae

Full plastomes and nuclear sequences show that Chandrasekharania and Jansenella are distinct from all other accepted tribes in Panicoideae and form a well-supported sister group of the large C4 clade Andropogoneae-Arundinelleae. Jansenella had first been placed in Arundinelleae (which then also included what is now tribe Tristachyideae), but differed from most of its members by a combination of morphological characters: a punctiform hilum, membranaceous ligule, lemma of the upper floret with two tufts of hairs at the base of the two lobes, and especially the two-keeled, two-toothed palea of the upper floret with unusual onecelled hairs. These characters were observed in J. griffithiana and led to its segregation from Danthoniopsis by [START_REF] Bor | Notes on Asiatic grasses: XXIII. Jansenella Bor, a new genus of Indian grasses[END_REF]. The later described J. neglecta is very similar and was presumably confounded with J. griffithiana before [START_REF] Yadav | On the identity of Jansenella griffithiana (Poaceae) with a new species from Western Ghats, India[END_REF]. Chandrasekharania was not assigned to any known group at its description but shared the morphology of the upper floret's lemma and the punctiform hilum [START_REF] Nair | Chandrasekharania: A new genus of Poaceae from Kerala, India[END_REF].

Basic chromosome numbers are synapomorphic for many grass clades (Kellogg 2015), and in the core Panicoideae, Paspaleae was separated from the x = 9 Paniceae based on phylogeny and its basic chromosome number of x = 10 ( [START_REF] Morrone | Phylogeny of the Paniceae (Poaceae: Panicoideae): integrating plastid DNA sequences and morphology into a new classification[END_REF]. This ancestral number indeed appeared to be a synapomorphy for the Paspaleae-Andropogoneae-Arundinelleae clade, classified as supertribe Andropogonodae by [START_REF] Soreng | A worldwide phylogenetic classification of the Poaceae (Gramineae) II: An update and a comparison of two 2015 classifications[END_REF]. In Jansenella-Chandrasekharania, chromosome numbers have only been determined for J. griffithiana to our knowledge: [START_REF] Christopher | Studies on the cytology and phylogeny of South Indian grasses. I. Subfamilies Bambusoideae, Oryzoideae, Arundinoideae and Festucoideae[END_REF] found a diploid number of 20, and [START_REF] Phipps | Studies in the Arundinelleae (Gramineae): IX. Chromosome numbers of 21 species[END_REF] 2n = 40, suggesting two ploidy levels. While data for the other two species would be desirable, this tentatively suggests an ancestral number of x = 10 for the Jansenella-Chandrasekharania clade and is in agreement with its position sister to Andropogoneae-Arundinelleae. We observed two copies of all nuclear genes studied in J. neglecta, of which one was always closer to J. griffithiana (Figs III.2 and III.3). The divergence of the two species' plastomes was estimated to the Quaternary (Fig. III.1). This strongly suggests that J. neglecta is an allopolyploid, with J. griffthiana or a recent ancestor as one of the parent species. It is possible that the 2n = 40 specimen of [START_REF] Phipps | Studies in the Arundinelleae (Gramineae): IX. Chromosome numbers of 21 species[END_REF] was in fact J. neglecta. Its source locality, Mahabaleshwar, falls into the known range of that species in the Western Ghats, but both species appear to be widely sympatric [START_REF] Yadav | On the identity of Jansenella griffithiana (Poaceae) with a new species from Western Ghats, India[END_REF].

Chandrasekharania and Jansenella were thought to have a C3 photosynthetic pathway based on leaf anatomy: in an early investigation in Arundinelleae s.l. (including Tristachyideae), [START_REF] Conert | Beiträge zur Monographie der Arundinelleae[END_REF] observed a radiate, Kranz-like chlorenchyma and single bundle sheaths, as in other members of the tribe, for J. griffithiana, and this was cited without further analyses by [START_REF] Metcalfe | Anatomy of the monocotyledons. I. Gramineae[END_REF]. [START_REF] Türpe | Sobre la anatomía foliar de Jansenella griffithiana[END_REF] performed a detailed leaf anatomical study in J. griffithiana. She observed double bundle sheaths, with few chloroplasts, but did not discuss photosynthetic pathway. Türpe's drawings were cited as evidence for a C3 pathway by [START_REF] Clayton | Genera graminum. Grasses of the World[END_REF], who also reported that the leaf anatomy of Ch. keralensis was "almost identical" to J. griffithiana. [START_REF] Renvoize | A survey of leaf-blade anatomy in grasses II. Arundinelleae[END_REF] confirmed the (partially) radiate chlorenchyma for J. griffithiana but identified it as C3 because of an adaxial palisade chlorenchyma and more than four cells between vascular bundles. [START_REF] Watson | Grass genera of the world. Available at: deltaintkey[END_REF] reported Jansenella as "supposedly C3" based on the drawings of [START_REF] Türpe | Sobre la anatomía foliar de Jansenella griffithiana[END_REF] but added that further study was needed.

Here, we found that the ppc-B2 gene recruited for primary carbon fixation in most C4 species shows a C3 signature in Ch. keralensis and the two species of Jansenella. This also explains the position of their ppc-B2 sequences in a basal grade of C3 grasses in the ppc-B2 phylogeny, distinct from the C4 cluster (Fig. III.3;[START_REF] Salamin | C4 photosynthesis evolved in grasses via parallel adaptive genetic changes[END_REF]. Most importantly, no serine, typically present in C4 grasses [START_REF] Salamin | C4 photosynthesis evolved in grasses via parallel adaptive genetic changes[END_REF], was found at position 780 in either ppc-B2 or any of the other ppc paralogs. Sites in the chloroplast gene rbcL under selection in C4 grasses [START_REF] Piot | One third of the plastid genes evolved under positive selection in PACMAD grasses[END_REF]) also showed a signature closer to C3 species. This genetic evidence thus supports both genera as C3 grasses, but further data such as carbon isotope ratios would be useful. Some of the presumably intermediate anatomic traits could be explained by inheritance from the common ancestor with Andropogoneae-Arundinelleae that may have already featured some C4 predispositions. Such "anatomical enablers", present in C4 taxa and their close relatives, are common in the PACMAD clade [START_REF] Osborne | Anatomical enablers and the evolution of C4 photosynthesis in grasses[END_REF].

Taken together, the phylogenetic position of Chandrasekharania and Jansenella sister to Andropogoneae-Arundinelleae, in combination with their morphology, karyology and photosynthetic pathway would justify recognising them as separate tribe within Panicoideae. This newly discovered sister group will be of interest for comparative studies on the genetic basis of C4 photosynthesis in Andropogoneae-Arundinelleae [START_REF] Besnard | Evolutionary genomics of C4 photosynthesis in grasses requires a large species sampling[END_REF]. Given the rarity especially of Ch. keralensis, the phylogenetic uniqueness of this clade also underlines its conservation value and calls for better data on its distribution.

Biogeography of Andropogoneae-Arundinelleae and the origin of Indian grasslands

The C4 sister tribes Andropogoneae and Arundinelleae both have their highest diversity and endemism on the Indian subcontinent (Fig. III.4). Their sister group Jansenella-Chandrasekharania has two species endemic to India, and one found from India to South-east Asia. These patterns, although not in themselves sufficient evidence, suggest that the divergence of these clades, and the transition to C4 photosynthesis in Andropogoneae-Arundinelleae, occurred on the subcontinent. [START_REF] Hartley | Studies on the origin, evolution and distribution of the Gramineae. I. The tribe Andropogoneae[END_REF] already noted the high diversity of Andropogoneae in India. Further evidence supports an Indian origin: the species Lasiurus scindicus, here supported as the earliest-diverging Andropogoneae, has two cytotypes, of which the 2n = 18 one is found in India and Pakistan and the 2n = 56 one in North Africa [START_REF] Faruqi | Studies in Libyan grasses X: Chromosome number and some interesting features[END_REF], suggesting westward dispersal from Asia. A South Asian origin was inferred for both the core Andropogoneae genus Themeda and the species Th. triandra, one of the dominant savannah grasses from Africa through Australasia (Dunning et al. submitted).

India has been connected to the rest of Eurasia since around 40-50 Ma (Ali & Aitchison 2008[START_REF] Bouilhol | Dating the India-Eurasia collision through arc magmatic records[END_REF] but is isolated through the Himalayas to the north, which restrict dispersal of tropical taxa and favoured radiations on the subcontinent [START_REF] Karanth | An island called India: phylogenetic patterns across multiple taxonomic groups reveal endemic radiations[END_REF]. The monsoon climate which affects most of the Indian Ocean region originated in the Late Eocene, creating seasonally alternating high rainfall and aridity [START_REF] Licht | Asian monsoons in a late Eocene greenhouse world[END_REF]. This seasonality increased with intensified Himalayan orogeny in the Mid-Miocene, around 15 Ma [START_REF] Ganjoo | Middle Miocene pedological record of monsoonal climate from NW Himalaya (Jammu & Kashmir State), India[END_REF]. The first stable-isotope evidence for C4 plants in the Siwaliks of India and Pakistan date to 9-6 Ma [START_REF] Quade | Expansion of C4 grasses in the Late Miocene of Northern Pakistan: evidence from stable isotopes in paleosols[END_REF][START_REF] Nelson | Isotopic reconstructions of habitat change surrounding the extinction of Sivapithecus, a Miocene hominoid, in the Siwalik Group of Pakistan[END_REF][START_REF] Sanyal | Intensification of monsoon, microclimate and asynchronous C4 appearance: Isotopic evidence from the Indian Siwalik sediments[END_REF][START_REF] Singh | Late Miocene record of palaeovegetation from Siwalik palaeosols of the Ramnagar subbasin, India[END_REF]) and are concordant with the global rise of C4 grasslands in the Late Miocene (Edwards et al. 2010). We here estimated the divergence of Jansenella-Chandrasekharania from Andropogoneae-Arundinelleae to the Early Miocene, around 22.6 Ma (Fig. III.1, Table III.1). The split of the two C4 tribes occurred roughly 3 Myr later, with a median of 19.5 Ma and a lower 95% HPD bound of 13.8 Ma. The transition to C4 photosynthesis would thus have occurred several million years before the Late Miocene grassland spread and the first isotopic C4 evidence on the subcontinent, but at a time of increased seasonality. The later C4 diversification would however have been concomitant with grassland expansion. [START_REF] Estep | Allopolyploidy, diversification, and the Miocene grassland expansion[END_REF] estimated that many Andropogoneae lineages had an allopolyploid origin, most of them in the Late Miocene or after. Evidence from other taxa for Indian grasslands dating to A monsoon climate is thought to have been favourable to the evolution of C4 photosynthesis [START_REF] Sage | Photorespiration and the evolution of C4 photosynthesis[END_REF] and was in place when Andropogoneae-Arundinelleae diverged. Andropogoneae in particular are mostly species of mesic habitats, adapted to fast accumulation of biomass during the wet season which then promotes fire in the dry season [START_REF] Osborne | Atmosphere, ecology and evolution: what drove the Miocene expansion of C4 grasslands?[END_REF]. Within India, the Western Ghats mountain range captures much of the monsoon precipitation and features old-growth and diverse grasslands [START_REF] Vasanthy | Pollen analysis of late quaternary sediments: Evolution of upland savanna in Sandynallah (Nilgiris, South India)[END_REF][START_REF] Sukumar | Climate change and its impact on tropical montane ecosystems in Southern India[END_REF][START_REF] Sankaran | Diversity patterns in savanna grassland communities: implications for conservation strategies in a biodiversity hotspot[END_REF]. We could not further resolve patterns of diversity within India here because most of the country constitutes one single TDGW level-3 region (Fig. III.4). However, much of the diversity of Andropogoneae also appears to be concentrated in the west of the country [START_REF] Hartley | Studies on the origin, evolution and distribution of the Gramineae. I. The tribe Andropogoneae[END_REF]. The Western Ghats, a global hotspot of biodiversity, seem to have been the centre of radiations in Andropogoneae, e.g. in the genus Glyphochloa [START_REF] Gosavi | Molecular phylogeny of Glyphochloa (Poaceae, Panicoideae), an endemic grass genus from the Western Ghats, India[END_REF]. Three presumably endemic Arundinella species were also recently described from the region [START_REF] Sunil | A new species of Arundinella (Poaceae: Panicoideae: Arundinelleae) from Kerala, India[END_REF], Sunil et al. 2014, 2017).

In the newly found C3 sister group, J. neglecta and Ch. keralensis are both restricted to the Western Ghats [START_REF] Nair | Chandrasekharania: A new genus of Poaceae from Kerala, India[END_REF][START_REF] Yadav | On the identity of Jansenella griffithiana (Poaceae) with a new species from Western Ghats, India[END_REF]). Only J. griffithiana has a wider distribution, but always occurs at higher altitudes, and is widespread also in the Western Ghats [START_REF] Yadav | On the identity of Jansenella griffithiana (Poaceae) with a new species from Western Ghats, India[END_REF]. All three are annual, open-habitat species. In the Khasi hills of northern India (Megalaya), J. griffithiana was recorded in diverse grasslands, where it appeared to be slightly negatively affected by fire and grazing [START_REF] Shilla | Impact of fire and grazing on plant diversity of a grassland ecosystem of Cherrapunjee[END_REF]. The Jansenella-Chandrasekharania lineage may have emerged in the first open grasslands before they became dominated by C4 grasses. Possibly, the transition from C3 to C4 photosynthesis in Andropogoneae-Arundinelleae may have occurred in montane, seasonally humid grasslands resembling those found today in the Western Ghats. The C4 clade would then have diversified into lower areas during the Late Miocene. Alternatively, the C3 clade may have been present at lower altitudes but retreated to montane habitats after being outcompeted by the now more diverse C4 grasses.

To conclude, the sister relationship of Jansenella-Chandrasekharania and Andropogoneae-Arundinelleae suggests that the transition to C4 and the initial diversification of the large C4 clade occurred in India, potentially in the seasonally humid environment of the Western Ghats. From there, it would have spread into and dominated savannahs in Asia and other continents. Phylogenies with a sufficient species sampling for this large clade would allow to formally test this hypothesis. 5 Chapter IV: A metabarcoding method for the analysis of grass endophyte communities in Madagascar 1

Abstract

Fungal endophytes, living in plant tissues without causing disease, are widespread. In grasses, there are welldescribed examples of positive effects of leaf endophytes on the host plant that can even impact community and food web composition. Diversity of grass endophytes is much higher than the well known model species, particularly in the tropics, but community composition and structuring factors are unknown in most natural settings. Here, we developed a metabarcoding approach to study grass leaf endophyte communities in three regions of highland Madagascar. A total of 768 samples were collected from 58 grass species in three habitat types: open grassland, tapia woodland and forest. We amplified and sequenced the ITS2 region to describe fungal communities. Results show preferential amplification of grass DNA and recovered only few fungal OTUs. Grass ITS2 sequences recovered allowed testing the original species identification and highlighted some possible errors. Grass communities both based on original identification and ITS2 clustering clearly distinguished forest from grassland and tapia woodland. Among the few fungal OTUs recovered are species of Epichloë associating with temperate Pooideae grasses and recorded for the first time in Madagascar. While analysis of fungal communities was limited, the results suggest that our preservation method yielded sufficient DNA for metabarcoding, that the structure of mock communities was repeatable across PCRs, and that technical biases such as tag switching were manageable. Our dataset has rich associated ecological data and would benefit from re-analysis with more specific primers.

Introduction

Plants, like all higher organisms, associate with microbes (Zilber-Rosenberg & Rosenberg 2008). Symbioses with bacteria or fungi play a central role in the interaction of plants with their environment, through beneficial functions like improved biotic or abiotic resistance, or as pathogens [START_REF] Saikkonen | Fungal endophytes: a continuum of interactions with host plants[END_REF][START_REF] Reinhold-Hurek | Living inside plants: bacterial endophytes[END_REF]. Microbes growing within living tissues of plants without causing apparent symptoms, termed endophytes, are believed to cover a wide array of functions (Wilson 1995). Fungal endophytes in particular include well-characterised cases of mutualistic relationships, for example protection against stress through heat (Redman et al. 2002), salinity [START_REF] Rodriguez | Stress tolerance in plants via habitat-adapted symbiosis[END_REF], pathogens [START_REF] Arnold | Fungal endophytes limit pathogen damage in a tropical tree[END_REF], or herbivory [START_REF] Clay | Fungal endophytes of grasses and their effects on an insect herbivore[END_REF]. However, mutualism may shift to antagonism under certain environmental conditions [START_REF] Saikkonen | Fungal endophytes: a continuum of interactions with host plants[END_REF], and many fungal endophytes are believed to be latent pathogens (Wilson 1995). Whatever their precise function, bioactive compounds produced by endophytes are seen as a promising reservoir for natural product research [START_REF] Strobel | Endophytes as sources of bioactive products[END_REF][START_REF] Guo | Bioactive natural products from endophytes: a review[END_REF].

1 Results of this chapter have not been published elsewhere when this dissertation was completed. The study was devised by G. Fungal leaf endophytes associated with grasses (Poaceae), with the well-studied case of the ascomycete genus Epichloë (syn. Neotyphodium), have been a focus of research [START_REF] Saikkonen | Evolution of endophyte-plant symbioses[END_REF]). Several species of Epichloë have demonstrated positive effects on their host, increasing its fitness under various forms of abiotic stress and protecting it against herbivores and pathogens through alkaloid production (Clay & Schardl 2002). The symbiosis is characterised by co-evolution with vertical transmission through seeds, partial co-divergence of lineages and loss of sexual reproduction in the fungi [START_REF] Schardl | Coevolution by common descent of fungal symbionts (Epichloë spp.) and grass hosts[END_REF], Clay & Schardl 2002). Moreover, effects of the endophytes beyond the host level have been demonstrated in experiments: their presence was shown to impact the composition of plant communities [START_REF] Clay | Effects of insect herbivory and fungal endophyte infection on competitive interactions among grasses[END_REF], Clay & Holah 1999) and food webs (Omacini et al. 2001). They have also been of considerable interest to agronomists [START_REF] Malinowski | Ecological importance of Neotyphodium spp. grass endophytes in agroecosystems[END_REF]. However, most of this research was restricted to one model system, E. coenophiala associating with Lolium species, and its application to most natural systems remains to be tested [START_REF] Saikkonen | Model systems in ecology: dissecting the endophyte-grass literature[END_REF]. Epichloë species are restricted to the temperate grass subfamily Pooideae (Clay & Schardl 2002), but grasses are believed to associate with a much larger array of fungi over their cosmopolitan distribution [START_REF] Márquez | Non-systemic fungal endophytes of grasses[END_REF]. A genus close to Epichloë, Parepichloë, was described from tropical grass species in Africa and Asia, but its function in the host is unknown (White & Reddy 1998).

Endophytes in the tropics are still poorly investigated but thought to much more diverse than at temperate latitudes [START_REF] Arnold | Are tropical fungal endophytes hyperdiverse?[END_REF]. Time-intensive culturing techniques have mostly limited research to the isolation and description of particular species, mostly from trees (e.g. [START_REF] Arnold | Fungal endophytes limit pathogen damage in a tropical tree[END_REF][START_REF] Costa | Diversity of leaf endophytic fungi in mangrove plants of Northeast Brazil[END_REF]). Among the few examples of community-wide studies in the tropics, work in Panama based on isolation and culturing showed that leaf endophyte communities associated with forest understorey grasses were dominated by host generalists and structured by spatial distance (Higgins et al. 2011[START_REF] Higgins | Communities of fungal endophytes in tropical forest grasses: highly diverse host-and habitat generalists characterized by strong spatial structure[END_REF]. The rise of environmental metabarcoding has allowed to study communities at a larger scale and depth. For example, Zimmerman & Vitousek (2012) found that fungal communities of a single tree species varied strongly with environmental gradients in Hawaii. However, while advances have been made on the global biogeography and community ecology of soil fungi [START_REF] Tedersoo | Global diversity and geography of soil fungi[END_REF] or bacteria [START_REF] Martiny | Microbial biogeography: putting microorganisms on the map[END_REF], the factors structuring endophyte communities at different scales remain largely unknown in most natural habitats and especially so in the tropics [START_REF] Rodriguez | Fungal endophytes: diversity and functional roles[END_REF].

Grasses cover a large part of the terrestrial surface, with tropical grasslands alone accounting for roughly 20% (Parr et al. 2014). Tropical grasslands are of global importance, sequestering carbon, feeding large stocks of herbivores, and sustaining human livelihoods. Progress has been made on their definition, ecology and biogeography, underlining the importance of herbivory and fire (Ratnam et al. 2011, Lehmann & Parr 2016). Microbial symbionts of grasses have not been integrated in frameworks of tropical grassland ecology. Yet, they may potentially impact productivity, species composition, and herbivore-plant interactions, whether as mutualistic or pathogenic symbionts. Basic information on fungal endophytes in the tropics and in tropical grasslands in particular is lacking, including on taxonomic composition, host selectivity, and the importance of environmental versus spatial determinants of community assembly.

Here, we attempted to develop a metabarcoding method to study foliar fungal endophytes communities in grasses of highland Madagascar. Grasslands, in a mosaic with forest and woodland, dominate plateau landscapes of Madagascar, and are only beginning to receive more attention from ecologists and biogeographers (see Vorontsova et al. 2016 and chapter II). We sampled a large and phylogenetically diverse set of grasses from open grassland, woodland, and closed forest. Our goal was to establish whether the fungal communities present in the leaves could be analysed with a metabarcoding approach. This could then allow to study the importance of various structuring factors, such as host identity, host evolutionary history, habitat type, and distance. We collected leaves of grass species in 92 plots distributed over three regions of central Madagascar (Fig. IV.1) in April and May 2016. The highlands of central Madagascar are dominated by grasslands, in a mosaic with bushland, woodlands, and some remaining forests which are typically gallery forests along streams. One particular type of open woodland is tapia woodland, dominated by Uapaca bojeri (tapia) and other tree species, all endemic (Moat & Smith 2007). Forests and tapia woodland are primary vegetation, rich in diversity and endemics, while the status of the open grasslands is controversial (see chapter II). The three protected areas we collected in are: (i) Ankafobe (34 plots), a small reserve covering a remnant gallery forest and surrounding grassland next to a national road; (ii) Ibity (12 plots), a mountain massif featuring abundant tapia woodland; (iii) Itremo (46 plots), a large and relatively isolated quartzite plateau featuring grassland, tapia woodland, and larger remnants of humid gallery forest. All sampling sites ranged from approximately 1300 to 1650 m elevation a.s.l. Necessary permits for collection and sample export were obtained before fieldwork.

Materials and Methods

Field sampling

Plots were established during random walks in each region, ensuring at least 100 m distance between them. They were placed in three types of vegetation: (i) open grassland, (ii) tapia woodland and (iii) forest. Plots at the edge of forests, often disturbed, were also classified as forest. In every plot, we collected eight grass specimens within a 5-m radius. We collected 1-4 specimens for 3-8 species per plot, depending on local diversity, with at least 1 m distance between specimens. We collected healthy-looking individuals, if possible with inflorescences, and stored them in individual plastic bags. Location, elevation, slope, estimated ground and canopy cover, the total number of grass species, and, if present, signs of disturbance and recent fires, were recorded for each plot.

Grass specimens were treated in the field camp maximum five hours after collection. For some, we kept voucher material (herbarium M. S. Vorontsova, K/TAN). We selected 3-5 intact leaves from each specimen. These were surface-sterilised by sequential washes of roughly 30 s each in 70% ethanol, 2% sodium hypochlorite and 90% ethanol, and finally rinsed with sterile water (following U'Ren et al. 2014 but with shorter immersion times). A segment of 2-5 mm was then cut from the middle of each leaf. Tweezers and scissors were sterilised by flaming over an alcohol lamp between specimens. Leaf segments were pooled per specimen and preserved in 2× CTAB buffer solution in a 200-µl well of a 96-well plate. Sample plates were stored in a styrofoam box buffered against heat with bottles of cold water. They were transferred to a refrigerator at ~8 °C upon the return from each field trip; the maximum time before refrigeration was 11 days. During air transit to France, samples were again kept in a styrofoam box and then stored at 4 °C.

DNA extraction, amplification and sequencing

DNA was extracted using the Wizard® Genomic DNA Purification Kit (Promega, Fitchburg, WI). For each sample, leaf segments were transferred with flame-sterilised tweezers to a tube with 300 µl of Nuclear Lysis Solution (NLS) and a 3-mm sterilised steel grinding ball. Samples were ground in a Tissue Lyser (Quiagen, Hilden) for 2×2 min, flipping them halftime through, at a speed of 30 s -1 . After 20 min waiting time at room temperature to reduce foam, the grinding balls were removed and another 200 µl NLS added. Tubes were then incubated at 65 °C for 30 min. After cooling down for 5 min, 50 µl of Protein Precipitation Solution were added, tubes were vortexed and then centrifuged for 15 min at 13,000 rpm. One hundred µl of the supernatant was transferred to a new tube with 600 µl isopropanol, avoiding foam from the top of the liquid. Tubes were inversed ten times and then centrifuged for 15 min at 13,000 rpm to precipitate DNA. The supernatant was discarded and 100 µl ethanol (95%) added to the pellet before centrifuging again for 10 min at 13,000 rpm. After discarding the supernatant, tubes were left open to dry for 3 h and DNA was then suspended in 100 µl nuclease-free water. Samples were handled under a laminar flow hood using filter-tip pipettes.

DNA was quantified with a Qubit fluorometer (Thermo Fisher Scientific, Waltham, MA) and samples were brought to equal concentration prior to amplification. Polymerase chain reaction (PCR) was performed using the primers ITS3 and ITS4 [START_REF] White | Analysis of phylogenetic relationships by amplification and direct sequencing of ribosomal RNA genes. PCR protocols: A guide to methods and applications[END_REF]) which target the nuclear ribosomal internal transcribed spacer 2 region (ITS2) and have been employed in fungal metabarcoding (e.g. [START_REF] Blaalid | ITS1 versus ITS2 as DNA metabarcodes for fungi[END_REF][START_REF] Tedersoo | Shotgun metagenomes and multiple primer pair-barcode combinations of amplicons reveal biases in metabarcoding analyses of fungi[END_REF]. Primers were tagged to allow for multiplexing, using different 8-bp tags for the forward and the reverse primer. The PCR mix per sample (total volume 15 µl) contained 7.5×10 -3 µmol of each of the primers, 150 µg bovine serum albumin, 7.5 µl AmpliTaq Gold® 360 Master Mix (Thermo Fisher Scientific, Waltham, MA) containing a hot-start polymerase, and 0.25 ng template DNA. We prepared nine 96-well PCR plates containing randomly shuffled samples as well as one positive and one negative control. The positive control was a mock community prepared with DNA extracted from pure cultures of eight fungal species unlikely to be found in plant leaves (Annex 1). A diagonal of eight wells was left empty, thus not using eight possible tag combinations per plate, which would allow estimating the frequency of tag switches. The PCR program included 10 min of initial denaturation and polymerase activation at 95 °C, followed by 30 cycles of 30 s denaturation at 95°C, 30 s annealing at 51.5 °C, 1 min elongation at 72 °C, and 7 min final elongation at 72 °C. PCR success was checked with gel electrophoresis.

The sequencing library was prepared and the sequencing run performed by the GeT-PlaGe core facilities of Genotoul (Toulouse, France). High-throughput parallel sequencing was done in a single, paired-end 2×250 bp run on an MiSeq machine (Illumina, San Diego, CA).

Sequence data processing

Reads obtained from the sequencing run were analysed using the obitools suite [START_REF] Boyer | obitools: a unix-inspired software package for DNA metabarcoding[END_REF]. Forward and reverse reads were first quality-checked by calculating mean phred scores for the entire reads and for the first and last 10 nucleotides. Paired reads were merged and then matched to samples by their tag combinations, accepting two mismatches for primers and removing primer and tag sequences in the same step. In a subsequent quality filtering step, reads shorter than 150 bp, containing any ambiguities or with a paired-read alignment score <50 were discarded. Reads were dereplicated and any singletons removed. Reads were then clustered into Operational Taxonomic Units (OTUs) with sumaclust [START_REF] Mercier | SUMATRA and SUMACLUST: fast and exact comparison and clustering of sequences[END_REF], applying a threshold of 97% pairwise identity commonly used in fungal metabarcoding (Lindahl et al. 2013). To identify fungal reads and match them to known taxa, we used the curated UNITE collection (Kõljalg et al. 2013), in version 7.2 of the general release with 49,407 fungal ITS sequences, as reference database. The ecotag program of the obitools was used to assign taxonomic ranks and names to the most abundant sequence of each cluster, applying a minimum identity of 95%.

Grass barcoding and community structure

In some cases, the original identification of grass species in the field was doubtful, particularly in the genera Oplismenus, Hyparrhenia and Digitaria, and in some specimens collected without inflorescence. In Hyparrhenia in particular, we were unsure about the distinction between H. rufa and H. schimperi. Thus, we amplified a short, ~660 bp barcode segment of the matK chloroplast gene for 52 samples, using previously described primers and protocols (GPWG II 2012). The barcode sequences were checked via alignments against available sequences of the species in question (see chapter II), using single-nucleotide polymorphisms and in some cases indels to differentiate groups.

Grass community structure was visualised with non-metric multidimensional scaling (NMDS), using the metaMDS function of the R package vegan [START_REF] Oksanen | vegan: community ecology package version 2[END_REF] with Bray-Curtis distances based on presence-absence data. We also looked at phylogenetic community structure, based on a phylogeny extracted from the grass supertree of chapter II. Three species not included in that phylogeny were replaced by others: Andropogon trichozygus was represented by A. eucomus ssp. huillensis which was identical on the markers analysed (see chapter II); Arundinaria itremoensis was the only bamboo in our samples and represented by the closely related A. humbertii; Hyparrhenia variabilis was represented by H. cymbaria to which it was most similar based on matK. Using the R package picante [START_REF] Kembel | Picante: R tools for integrating phylogenies and ecology[END_REF], we calculated phylogenetic diversity (PD, Faith 1992) and two measures of phylogenetic structure (clustering vs. overdispersion, [START_REF] Webb | Exploring the phylogenetic structure of ecological communities: an example for rain forest trees[END_REF], the net relatedness index (NRI) and the nearest taxon index (NTI), both inferred by comparisons against 999 randomisations of the community matrix where species richness per plot was maintained. We visualised community structure by habitat to see if grassland, forest, and tapia woodland could be distinguished.

As the DNA primers unintentionally amplified plant rather than fungal DNA (see Results), we made use of these data by checking the congruence of ITS2 genetic clusters with grass identifications by morphology and matK sequences. For this, we first extracted the most common read per sample. The extracted reads were then clustered with sumaclust as described above, but using a threshold of 98% identity. This matched the original species identification quite well while over-splitting species slightly. The most abundant read per cluster was checked via BLAST searches [START_REF] Altschul | Basic local alignment search tool[END_REF]) against GenBank as implemented in Geneious v. 9.0.5 (Biomatters, Auckland). The clusters were then used to repeat NMDS of community structure as described above.

Fungal diversity

The original goal of analysing fungal endophyte community structure was compromised by the preferential amplification of plant DNA (see Results). We thus focused our analysis on the sequenced mock community and the taxonomic identity of the few fungal OTUs recovered. First, we checked the abundance of the mock community OTUs over the nine PCR plates to see whether community structure and abundance were repeatable. Second, we quantified the occurrence of mock OTUs in other samples, which would indicate either tag switches or cross-contaminations. Finally, we excluded all controls and removed OTUs with a count of <25 reads per sample, based on the estimations of tag switches and mock OTUs occurring in other samples. Of the remaining OTUs, we submitted the most abundant read for those occurring in more than one sample to BLAST searches against GenBank to check the taxonomic assignment by ecotag. We did not further analyse fungal community structure because of the low number of OTUs; test NMDS runs did not converge, suggesting insufficient information in the data.

Finally, we extracted the most abundant reads for two OTUs identified as Epichloë. We aligned them, using the E-ins-i option of MAFFT (Katoh & Standley 2013), with complete ITS sequences from GenBank, including all identified Epichloë species available, the respective closest BLAST matches, and four Balansia species as outgroup. A Maximum Likelihood phylogeny was inferred with RAxML (Stamatakis 2014), applying a GTR+G substitution model and performing 1000 bootstrap pseudoreplicates.

Results

Data quantity and quality

From 92 plots, we collected a total of 768 samples belonging to 58 grass species; 512 were from grassland, 104 from tapia woodland and 152 from forest. Sequencing yielded a total of 12,444,774 raw paired-end reads. Mean phred quality was >25 in the large majority of the samples, but reverse reads overall had lower quality, especially at the 3' ends (Fig.

Grass identification and community structure

The 58 grass species sampled were phylogenetically diverse, but the majority belongs to subfamily Panicoideae (Fig. IV.3). The use of matK barcodes confirmed the distinction of three Digitaria species but suggested that Hyparrhenia rufa and H. schimperi were very close and could not be reliably distinguished; these were thus considered as one species, H. cf. rufa. Two C4 species dominating grassland and tapia woodland plots, Loudetia simplex and Schizachyrium sanguineum, account for roughly one third of the samples. In forest plots, a clade of closely related C3 species with many endemics accounts for most samples (Fig. IV.3). Plots from all three habitats types had a mean species richness of six, but grassland and tapia had a higher mean phylogenetic diversity ( Plant ITS2 sequences were the dominant reads in all but 11 samples. Clustering of ITS2 sequences overall confirmed species identifications and matK barcoding. However, 23 samples were assigned to clearly aberrant clusters, which were mostly from the same habitats. Schizachyrium sanguineum split in two ITS2 clusters of 45 samples each, while the marker

q:, • • • • ' • 0 0 0 0 0 1 : 0 •• • • Forest • • •'• o Grassland o Tapia woodl.
--,---,-

1 1 1 1 J 1 1 J 0 0 0 -----î- Il 0 1 J B 1 1 0 1 J 0 •c3 z t•
O. compositus. These discrepancies did not affect the distinction of forest grass communities from tapia woodland and grassland through NMDS (Fig

o !ô • • Oo N N • • • •• Cf) 0 Cf) 0 d <Sb • 0 0 0 g •• • • • • 0 • ' 0 ' 1 -1 0 1 2 3 -1 0 1 2 3 MDS1 MDS1 Figure IV.5.
Differentiation of grass communities by habitat, visualised through non-metric multidimensional scaling (NMDS). NMDS was performed based on both original identification supported through matK barcodes as well as 98% identity ITS2 clusters, based on Bray-Curtis distances of presence-absence data.

0 0 --,- 1 TDB e --,- 1 □ j_ 1 1 J B --,- 1 1 --,- 1 1 1 1 0 --,- 1 1

Endophyte diversity

The 104,563 quality-filtered reads identified as fungi clustered in 398 OTUs. In the mock communities, six out of eight species were always recovered, while two, Paxillus adelphus (Basidiomycota) and Glonium stellatum (Ascomycota), were not found and apparently failed to amplify. Read numbers and abundance ranks of mock OTUs were repeatable, with an outlying lower yield only in plate 4 (Fig. IV.6a). Yield overall increased with the amount of mock OTU template DNA but revealed strong taxon-specific variability (Fig. IV.6b). Among the six amplified mock OTUs, no general bias towards ascomycetes or basidiomycetes was observed. Reads of the most abundant mock OTUs were also found in other samples, but with a maximum number of 23. Excluding mock OTUs and all occurrences with less than 25 reads, only 38 OTUs were left of which 22 were only found in one sample (Table A-IV.1 in annex A-IV). Most were only assigned to the fungal kingdom by ecotag but several could be assigned to genera or higher-level ranks by BLAST searches against GenBank. The most frequent OTU, found in 12 samples, had 100% identity with several Phoma and Epicoccum species, including the sorghum grain mold fungus Epicoccum sorghinum. It was associated with various genera, including Aristida, Hyparrhenia, and Schizachyrium. Two OTUs were identified as Clavicipitaceae by ecotag and could be assigned to Epichloë through BLAST searches. One was found in the single sample of Festuca camusiana, collected in the shade in a tapia woodland plot, the other in the three samples of Brachypodium madagascariense, all from forest plots. This means that all four Pooideae samples contained Epichloë. An ITS phylogeny of the genus was overall not well resolved but placed the F.-camusiana-associated OTU with two other Loliinae-associated species (E. occultans and E. uncinata) while the OTU associated with B. madagascariense was distinct but without supported close relatives (Fig. IV.7). One OTU from the F. camusiana sample classified as fungal by ecotag was identified as Festuca through BLAST searches (Table A-IV.1).

Discussion

The analysis we present here is preliminary and was hampered by the unintended amplification of plant DNA. Nevertheless, some conclusions can be drawn that will help direct future re-analysis of the dataset. First, we found that grassland and forest had not only distinct grass species communities but also differed in phylogenetic structure. Forest communities are phylogenetically clustered, which can be explained by the dominance of one particular panicoid clade, the "Madagascar shade clade" (see chapter II). Grass communities in tapia woodland are more similar to grassland but also feature some particular species (Fig. 3). This is in line with results from a larger sample of grass communities in central Madagascar (C. Solofondranohatra et al. submitted). In any case, this means that host grass phylogeny should be included as variable in a future analysis of endophyte community structure, given its interaction with habitat.

Primers for amplifying the ITS2 region were chosen because there is thought to be a potential sequencing bias in ITS1 against ascomycetes due to an upstream SSU intron (Lindahl et al. 2013), and ascomycetes are the dominant group among endophytes [START_REF] Rodriguez | Fungal endophytes: diversity and functional roles[END_REF]). The primers ITS3 and ITS4 have been employed since more than 25 years in fungal ITS sequencing [START_REF] White | Analysis of phylogenetic relationships by amplification and direct sequencing of ribosomal RNA genes. PCR protocols: A guide to methods and applications[END_REF]) and were also used in metabarcoding studies of soil and root-associated fungi (e.g. [START_REF] Blaalid | ITS1 versus ITS2 as DNA metabarcodes for fungi[END_REF][START_REF] Tedersoo | Shotgun metagenomes and multiple primer pair-barcode combinations of amplicons reveal biases in metabarcoding analyses of fungi[END_REF]. A comparison of different primer sets found ITS3/ITS4 to have fungal coverage comparable to other ITS2 primers and at least one mismatch in each primer to embryophytes [START_REF] Toju | High-coverage ITS primers for the DNA-based identification of ascomycetes and basidiomycetes in environmental samples[END_REF]. It is possible that for analysis of the leaf microbiome where plant DNA is dominant, stronger discrimination is necessary. Also, preferential amplification specific to Poaceae cannot be excluded. Metabarcoding studies of leaf endophytes that did use the ITS1 region recovered a majority of ascomycetes (e.g. Cordier et al. 2012[START_REF] Bálint | Relocation, high-latitude warming and host genetic identity shape the foliar fungal microbiome of poplars[END_REF], suggesting the potential bias is weak. Sequencing the whole ITS region (500-600 bp), the accepted fungal barcode [START_REF] Schoch | Nuclear ribosomal internal transcribed spacer (ITS) region as a universal DNA barcode marker for Fungi[END_REF], would be desirable but is not feasible with current Illumina technologies which have a maximum sequencing length of 300 bp per direction. A future re-analysis of this dataset should explore the use of the ITS1 region but specifically test the primers against grasses first using in silico PCR [START_REF] Ficetola | An In silico approach for the evaluation of DNA barcodes[END_REF].

The preferential recovery of plant ITS2 sequences, while unintended, allowed to highlight some potential cases of confusion or misidentification of grass species. These are possible since especially the open grass communities are very dense and individuals can be easily confused. Exclusion of samples with conflicting identification would probably be most conservative with regard to downstream analyses and would affect less than 5% of the samples. Close species that were sometimes confused, such as Oplismenus species, or Panicum ambositrense and P. perrieri, should probably be lumped together. This would increase sample size for each species and mask processes such as hybridisation that may take place between close species but are not of interest at the scale of this study. Unrelated to the objective of endophyte community analysis, the plant ITS2 sequences generated may also allow to look at the genetic structure of grass populations from three distinct regions, which is relevant to the history of grasslands in Madagascar (see chapter II). Considering possible intragenomic ITS variability and polyploidy, a strategy to extract variants per individual and distinguish them from errors would have to be found.

Overall, the ITS2 analysis suggests that metabarcoding is a suitable tool to study endophyte communities even in remote locations. In the absence of better options for preservation and cooling in the field, storage in CTAB buffer appears to yield sufficient quantity and quality of DNA. U'Ren et al. ( 2014) also suggested that CTAB preservation is preferable over silica drying when direct freezing is not feasible. Our analysis also suggests that while tag switches do occur [START_REF] Carlsen | Don't make a mista(g)ke: is tag switching an overlooked source of error in amplicon pyrosequencing studies?[END_REF], they do so at very low levels relative to the total number of reads. They can thus be controlled for by removing reads below an estimated abundance threshold. In our study, this removed most of the presumed fungal OTUs, some of which may be true occurrences. However, this is rather a problem of very low coverage relative to reads of plant origin, which should be resolved with more appropriate primers (see above). The use of a mock community demonstrated that PCR, while showing bias among taxa, yields repeatable community composition as long as there is sufficient sequencing depth [START_REF] Smith | Sequence depth, not PCR replication, improves ecological inference from next generation DNA sequencing[END_REF]. The assignment of OTUs to fungal taxa could be improved; here, our first goal was to recover those OTUs that are fungal so we chose a rather conservative limit of 95% identity. This means that the most common ancestor of all reference sequences similar to an OTU, including many unidentified environmental samples, could not be resolved further than to the kingdom Fungi by ecotag. The use of all fungal sequences available on GenBank, whose identification is less certain but which provide a higher number of references, should be explored. The assignment of a Festuca sequence as fungal by ecotag moreover highlights potential errors, even in expert-curated databases such as UNITE (Kõljalg et al. 2013).

The few fungal OTUs recovered support the idea that many endophytes are latent pathogens (Wilson 1995): an OTU identified as Epicoccum and close to the common pathogen E. sorghinum was the most widespread. That species was recently recovered through metabarcoding from sorghum seeds in Burkina Faso [START_REF] Stokholm | DNA barcoding and isolation of vertically transmitted ascomycetes in sorghum from Burkina Faso: Epicoccum sorghinum is dominant in seedlings and appears as a common root pathogen[END_REF], suggesting vertical transmission and making an endophytic life stage plausible. However, the complete identity of the OTU's ITS2 sequence with several Epicoccum accessions on GenBank suggests that ITS may not be sufficient to distinguish species in this group, a conclusion reached by [START_REF] Gazis | Species delimitation in fungal endophyte diversity studies and its implications in ecological and biogeographic inferences[END_REF] for other groups of endophytes. A significant result of our study is the confirmation of Epichloë endophytes in all four Pooideae samples analysed. This is, to our knowledge, the first record of Epichloë in Madagascar. The ITS phylogeny (Fig. IV.7) tentatively suggests that the two OTUs are distinct species and do not have a common origin. Epichloë species have been found in various temperate regions of the world, always associated with Pooideae, and have a demonstrated co-divergence history of some subgroups with the grass subfamily [START_REF] Schardl | Coevolution by common descent of fungal symbionts (Epichloë spp.) and grass hosts[END_REF], Clay & Schardl 2002). It is likely that they co-dispersed to Madagascar with the ancestors of the endemic B. madagascariense and F. camusiana, potentially with seeds given the possibility of vertical transmission.

The original objective of our study was an analysis of fungal endophyte community structure across several habitats, regions, and grass species. The goal was notably to distinguish habitat and host filters from neutral factors such as dispersal limitation by distance. Our dataset includes a large number of samples and covers a wide range of potential ecological factors, with 58 grass species from contrasting habitats, a spatially explicit sampling, and a full phylogeny of the host grasses. Re-analysis with more appropriate primers would give valuable insights into endophyte community structure in a region completely unknown in terms of fungal endophytes.

Conclusion and perspectives

Lineage dispersal in grasses

In this dissertation, I studied the dispersal history of a globally distributed plant family, the grasses. Chapter I explicitly looked at factors underlying dispersal in one temperate grass lineage. Chapter II analyses the origins and timing of arrival of the various lineages that constitute the extant grass flora of Madagascar. Chapter III placed a small C 3 lineage in the grass phylogeny, confirming a position that suggests its sister lineage, of the largest known C 4 clades, originated in and dispersed out of India. Chapter IV, despite technical limitations, demonstrated the presence of vertically transmitted endophytes in Madagascar, suggesting potential co-dispersal with their host grass lineages.

Lineage dispersal has only become accessible to statistical inference with the arrival of molecular phylogenetics and especially divergence time estimation (see Introduction). Rather than rare and elusive, it appears to be a central process in the biogeography of at least plants [START_REF] Renner | Plant dispersal across the tropical Atlantic by wind and sea currents[END_REF][START_REF] Sanmartín | Southern hemisphere biogeography inferred by event-based models: plant versus animal patterns[END_REF]. Higher plants, with their embryos well protected in seed coats, have an excellent vehicle allowing transport even over large distances and under rough conditions. Large seeds with hard shells such as the sea-travelling coconuts are the best examples for global dispersal, but it appears that long-distance dispersal is common even in rather small-seeded groups such as grasses (chapters I and II, Blattner 2006, Inda et al. 2008, Linder et al. 2013). Grass seeds have a well developed, starchy endosperm that provides a nutrient reservoir, while the double wall structure of the caryopsis, where the fruit wall is fused with the seed coat, additionally protects the seed (Kellogg 2015). Dispersal units sometimes not only include the caryopsis, but whole spikelets or clusters of spikelets, which may have hooks or barbs that facilitate dispersal (Kellogg 2015). Many bird species feed on grass seeds (e.g. Columbidae, [START_REF] Frith | Food of eight species of Columbidae, in the genera Geopelia, Phaps, Geophaps and Petrophassa[END_REF]) and represent a likely dispersal vector. Testing whether reconstructed dispersal routes are statistically associated with dominant migration routes of birds (Gillespie et al. 2012) would be worthwhile; range evolution analysis combined with stochastic mapping as employed in chapter I could be used for this. Large phylogenies such as now increasingly available for the grasses (Spriggs et al. 2014, for example, compiled a phylogeny for 3,595 species, i.e. 30% of the family) would provide the necessary sample size and statistical power.

A factor naturally expected to affect dispersal success is distance. Studies at the margin between ecology and biogeography have demonstrated "dispersal kernels" where dispersal probability drops off with distance (Nathan et al. 2003). Here, I inferred through statistical model comparison that distance is an important factor in one specific plant lineage, the Loliinae (chapter I), and in several lineages that contributed to the assembly of Madagascar's grass flora (chapter II). Surprisingly few studies have explicitly tested the role of distance in range evolution (e.g. Linder et al. 2013, Van Dam & Matzke 2016). Models such as DEC+x including this factor would certainly provide good fit to many phylogenies and probably improve ancestral area inference. It will be interesting to see, too, how the strength of dispersal limitation as measured by x differs between lineages, and how it is related to other factors such as dispersal vectors, barriers etc. However, it is not quite clear whether x can be directly compared when inferred on separate phylogenies where sample size, area definition, and distance measures differ; this will have to be tested using simulations. The parameter x alone also does not allow to estimate the shape of the dispersal kernel, which requires stochastic mapping. Unlike a study on danthonioid grasses (Linder et al. 2013), I could not confirm a "fat-tailed" dispersal kernel for the Loliinae (chapter I) where dispersal probability would essentially be independent from distance at very large distances (Nathan et al. 2003). This may be partly due to methodological choices, such whether "zero" dispersals between areas are counted as I did for the Loliinae example. Also, the shape of the dispersal kernel may not be the same for ecological dispersal and the "effective dispersal" (including establishment) usually inferred in biogeography. Again, the increasing number and size of phylogenies will allow to properly test hypotheses for different taxonomic groups.

Beyond factors that act on the dispersal process itself, successful establishment will determine dispersal rates and probabilities inferred from phylogenies. Plants are advantaged over most animals in that often a single individual may suffice to found a new population, as observed for example in an orchid [START_REF] Willems | Establishment and development of a population of Orchis simia Lamk. in the Netherlands, 1972 to 1981[END_REF]. Asexual reproduction, through vegetative growth or apomixis, is common in plants, including grasses [START_REF] Brown | Apomixis in the Gramineae: Panicoideae[END_REF][START_REF] Calzada | Apomixis: the asexual revolution[END_REF], Kellogg 2015). Moreover, the high frequency of polyploidisation, including between distinct species (Kellogg 2015), may improve local persistence and facilitate the recruitment of genes adaptive in a new environment. The invasive grass Spartina anglica, an anthropogenic polyploid hybrid, is a good example for this [START_REF] Gray | A century of evolution in Spartina anglica[END_REF]). In the grass subfamily Danthonioideae, long-distance dispersal events were found to be more likely in polyploid lineages [START_REF] Linder | Does polyploidy facilitate long-distance dispersal?[END_REF]) and several lineages resulted from new combinations of chloroplast and nuclear lineages through hybridisation (Pirie et al. 2009). Other mechanisms of horizontal transfer probably underlie the recruitment of C 4 genes from co-occurring but phylogenetically distant lineages observed in the model grass Alloteropsis semialata [START_REF] Edwards | Adaptive evolution of C4 photosynthesis through recurrent lateral gene transfer[END_REF]. Increasingly available data from various genomes (nuclear, mitochondrial, and chloroplastic) will probably reveal that such events of adaptation through recombination or horizontal transfers are more frequent than currently known [START_REF] Soucy | Horizontal gene transfer: building the web of life[END_REF]. Other traits conserved phylogenetically and already present at the time of dispersal may facilitate establishment. In chapter I, I inferred only weak support for dispersal rates differing between two clades with contrasting phenotypic syndromes (roughly, competitive vs. vagile). It may be useful to decompose such syndromes into individual traits and test if there are any key traits that affect dispersal and establishment. Rhizome strength, lateral spread, overall growth rate, seed production, and ploidy level (all southern hemisphere Loliinae appear to be polyploid, [START_REF] Catalán | Phylogeny and evolution of Festuca L. and related genera of subtribe Loliinae (Poeae, Poaceae)[END_REF], are candidate traits. Another factor affecting local establishment is that of microbial symbionts: frequently, plants will have to adapt to locally occurring microbial communities, but conservatism and co-dispersal of adapted symbionts is another possibility (see last section, below).

The assembly of tropical grasslands

The importance of tropical grasslands has been increasingly acknowledged over the last years (Parr et al. 2014, Bond 2016, Lehmann & Parr 2016). That grasslands expanded globally since the Miocene is supported by several lines of evidence (Edwards et al. 2010, Strömberg 2011). However, the status of many grasslands as natural or anthropogenic is debated (see e.g. Bond et al. 2008 for Madagascar, andRatnam et al. 2016 for Asian grasslands). Phylogenetic analyses of grass diversity (e.g. Vorontsova et al. 2016) represent one way to test whether grasslands are natural and to estimate their age. Here, I analysed grass diversification in Madagascar and found endemic C 4 clades diverging in the Miocene to Pleistocene, which supports the existence of C 4 habitats before human colonisation (chapter II). I also recovered a small lineage of Indian C 3 grasses that are found in grasslands and phylogenetically sister to one of the major tropical C 4 clades, supporting the ancient nature of Indian grasslands (chapter III). Such phylogenetic analyses are important to complement studies looking at the macroecological determinants of grasslands (e.g. [START_REF] Sankaran | Determinants of woody cover in African savannas[END_REF], Lehmann et al. 2011, Ratnam et al. 2011): they reveal patterns that may be specific and contingent on the regional context. For example, while both Madagascar and India were presumably affected by the Miocene grassland expansion, Madagascar saw repeated immigration of C 4 grasses, mainly from Africa (chapter I), while India was potentially the cradle of a major in situ C 4 clade diversification (chapter III). With more data available, future studies could compare the phylogenetic structure of grasslands in various regions of the world, identify bursts of diversification and evaluate the importance of local lineage recruitment versus immigration over larger distances (Donoghue 2008). The next step would be to couple phylogenetics with trait evolution and estimate how key traits related to fast growth, resprouting after fire, herbivore resistance, and drought resilience, accumulated over time, how trait diversification relates to niche space [START_REF] Walker | Equilibrium models of evolutionary species diversity and the number of empty niches[END_REF][START_REF] Freckleton | Detecting non-Brownian trait evolution in adaptive radiations[END_REF], and whether trait composition and phylogenetic diversity of grasses differ between types of grassland (e.g. herbivore-vs. fire-controlled, or mesic versus xeric) or between different regional contexts.

Phylogenetic analyses can only be large in scale and are hampered by the uncertainties of divergence time calibration (see general introduction and discussion in chapter II). Even if they may support the existence of C 4 grassy biomes before widespread human intervention, they provide no clues on how important and expansive these ancient grasslands were. Stable isotope analyses looking at the stability of forest-savannah boundaries through time (e.g. [START_REF] Desjardins | Changes of the forest-savanna boundary in Brazilian Amazonia during the Holocene revealed by stable isotope ratios of soil organic carbon[END_REF][START_REF] Wiedemeier | Stable forest-savanna mosaic in north-western Tanzania: local-scale evidence from δ 13 C signatures and 14 C ages of soil fractions[END_REF] as well as additional stratigraphic records of pollen, charcoal, and dung fungi (e.g. Burney 1987, Gasse & Van Campo 1998, Burney et al. 2003) could increase spatial and temporal resolution of grassland dynamics. Population genetic analyses may provide further evidence through the inference of past population contractions and expansions. Grasses, as the keystone species of grassy biomes, would be a natural subject for population genetics (such as done by McAllister & Miller 2016 for a North American grassland species); however, their often large populations mean that signatures of geographical structure may be difficult to detect. More sparsely distributed savannah plants with presumably short (ecological) dispersal distance, such as the "underground trees" (geoxylic suffrutices, Maurin et al. 2014) of Africa, or tapia (Uapaca bojeri) in Madagascar may be better suited to such analyses. Also, precisely those species not adapted to open habitats may give clues on the past extent of grasslands: in Madagascar, there is high local endemism in forest-dwelling species such as lemurs, and allopatric speciation through past fragmentation has been proposed as a mode of diversification on the island (Wilmé et al. 2006, Vences et al. 2009). The striking in situ diversification of forest grasses and bamboos (chapter II) may represent an equivalent pattern in plants. If forests were indeed fragmented and separated by the expansion of grassland, this could have restricted gene flow and favoured speciation. Thus, population genetics of open-habitat species would ideally be complemented with analyses of forest specialists in the same region.

Fungal endophytes of grasses

Looking beyond the grass phylogeny, the original objective of the last chapter (IV) was to study the community structure of symbionts associated with grasses. Whereas the first three chapters used phylogenies inferred from DNA to look back in time, here molecular methods were used to study diversity in space. The unintended amplification of plant rather than fungal DNA underlined the methodological challenges of such barcoding studies [START_REF] Taberlet | Towards next-generation biodiversity assessment using DNA metabarcoding[END_REF]. Nevertheless, some results suggest perspectives for future research.

First, grass communities from forest and open habitats (grassland and tapia woodland) had contrasting phylogenetic structure. This suggests that host phylogeny should be integrated in endophyte community analysis since it may, at least partly, explain potential differences between habitats. It may also allow to detect any host specificity that operates at a higher level than that of species. I expect however that forest and open habitats, independently from host phylogeny, harbour different fungal communities, as they represent environments with very different conditions for growth and dispersal. First, plant leaves in open grasslands are subject to high irradiation, a factor which is thought to require specific adaptations of the leaf microbiome and thus represent a strong selective force [START_REF] Vorholt | Microbial life in the phyllosphere[END_REF]. Second, higher airflow in open habitats may facilitate the contagious spread of fungal spores and homogenise communities over larger distances; this would create weaker spatial structure in grassland than in forest communities. Furthermore, the frequent fires which characterise tropical grasslands regularly consume most of the grass biomass [START_REF] Bond | Fire as a global "herbivore": the ecology and evolution of flammable ecosystems[END_REF]. I thus expect that latent saprotrophs have less abundant resources and may be under-represented among grassland endophytes compared to forest grasses. The most frequent OTU recovered in chapter IV, an Epicoccum species, is likely a latent pathogen, but this is only anecdotal evidence for any dominant lifestyle. Finally, grasslands in Madagascar -and elsewhere -have a grazing megafauna; these are mainly zebu cattle in modern Malagasy grasslands (including the ones sampled in chapter IV), but there was presumably a much more diverse grazing fauna less than a few thousand years ago [START_REF] Burney | Madagascar's prehistoric ecosystems. The natural history of Madagascar[END_REF]. Selective pressure through grazers may favour mutualistic fungi protecting their host through toxins, as do Epichloë in temperate Pooideae grasses. Less studied relatives of Epichloë found in tropical grasses, such as Balansia [START_REF] Reddy | An examination of molecular phylogeny and morphology of the grass endophyte Balansia claviceps and similar species[END_REF] and Parepichloë (White & Reddy 1998), may have similar functions, given the widespread occurrence of diverse alkaloids in the family Clavicipitaceae [START_REF] Schardl | Plant-symbiotic fungi as chemical engineers: multi-genome analysis of the Clavicipitaceae reveals dynamics of alkaloid loci[END_REF].

The discovery of Pooideae-specific Epichloë endophytes in Madagascar demonstrates the conservatism of this symbiosis even at tropical latitudes. Co-divergence of mutualistic Epichloë with their host plant lineages has been demonstrated (Clay & Schardl 2002), but no study has yet investigated the combined biogeography of symbionts and host plants to my knowledge. The low probability of randomly dispersed spores to find a host plant in the tropics, where Pooideae only occur in "mountain islands", and the frequent vertical transmission with seeds suggest that both dispersed together. If this is the case, phylogenies of Epichloë should show a north-to-south dispersal pattern as in the Loliinae (chapter I) and the Pooideae in general (Bouchenak-Khelladi et al. 2010). The frequent hybrid origin of mutualistic Epichloë species (Clay & Schardl 2002) complicates phylogenetic analyses, but it also suggests some interesting hypotheses on the relationship between hybridisation and dispersal. On one hand, hybrid taxa may be advantaged in new environments (see first section above) and thus more frequently associated with grass lineages derived from long-distance dispersal. Then again, the disjunct distribution of Pooideae in the Tropics may provide less opportunities for hybridisation. Such hypotheses could be tested with well-sampled phylogenies of Epichloë. Unfortunately, molecular data is mainly available from species that were isolated from readily accessible live plants, with a bias towards the northern hemisphere (e.g. [START_REF] Craven | Multigene phylogeny of Epichloë species, fungal symbionts of grasses[END_REF][START_REF] Li | A new species of Epichloë symbiotic with Chinese grasses[END_REF][START_REF] Charlton | Epichloë canadensis, a new interspecific epichloid hybrid symbiotic with Canada wildrye (Elymus canadensis)[END_REF], but see [START_REF] Moon | The evolutionary origins of three new Neotyphodium endophyte species from grasses indigenous to the southern hemisphere[END_REF][START_REF] Gentile | Origin, divergence, and phylogeny of Epichloë endophytes of native Argentine grasses[END_REF]. Modern sequencing technologies have allowed to recover not only highly represented chloroplast DNA, but also low-coverage nuclear loci from herbarium specimens (see e.g. chapter III). It may thus be possible to sequence the symbiont along with the plant, especially if the nuclear ribosomal complex, present in repeated copies and commonly used for fungal phylogenetics and barcoding, is targeted. Epichloë infections are typically systemic, i.e. the hyphae are present in most aboveground plant tissues (Clay & Schardl 2002). This is supported by the fact that all four Pooideae samples from Madagascar yielded Epichloë DNA despite the overall bias towards plant DNA (chapter IV). If fungal DNA could be recovered from herbarium material or silica-dried samples, this would open exciting perspectives for building well-sampled phylogenies, estimating dispersal histories, and confronting them with the evolutionary history of the host plants.

Annex 7.1 A-I (chapter I: Factors underlying the global dispersal of temperate Loliinae grasses)

A-II (chapter II: Grass diversification in Madagascar)

Taxon sampling and datasets

We aimed to analyse a representative set of molecular data for the grass flora of Madagascar and the wider Madagascar region, focusing especially on endemic species. To this end, we sampled specimens collected in the field since 2011 as well as herbarium specimens. We also included additional species putatively close to Malagasy taxa, especially for groups particularly diverse in Madagascar such as the Hickeliinae (Bambusoideae) and the Boivinellinae (Panicoideae). For some species with complex species-level taxonomy or a large distribution range, we included two or more specimens. Altogether, we produced new data for 238 specimens from Madagascar or nearby islands and 133 specimens from other areas. Including sequence data from GenBank (see below), an estimated 396 species occurring in Madagascar are represented in the phylogenies (73% of the known species diversity, including some putative new taxa; 77% of the known C3 species and 71% of the C4 species). Of these, 144 are endemic (65% of known endemics, 71% of the endemic C3 species and 59% of the endemic C4 species), and another four are endemic to Réunion, Glorioso or Europa Island.

Molecular data were organised in 11 datasets corresponding to major grass clades recovered in previous work, mostly subfamilies or large tribes (GPWG II 2012, Kellogg, 2015, Soreng et al. 2015), following the classification of Soreng et al. (2015): Oryzoideae, Bambusoideae, Brachypodieae, Poeae, Aristidoideae, Panicoideae (focusing on the "outlying Panicoideae" and Lecomtella, representing the large Andropogoneae-Arundinelleae, Paniceae and Paspaleae clades with two taxa each), Paniceae, Andropogoneae-Arundinelleae, Arundinoideae-Micrairoideae, Chloridoideae, and Danthonioideae. Total species sampling in these clades ranged from roughly 10% (Andropogoneae-Arundinelleae) to 65% (Brachypodieae). The clades Paspaleae and Pharoideae, present with two and one native species in Madagascar, respectively (Vorontsova et al. 2016), have no endemics and were not analysed here. Bromus was not analysed either as we were unable to collect the two endemic species.

DNA extraction, PCR, and sequencing

We selected three chloroplast genes, ndhF, rbcL, and trnK-matK, as molecular markers. This combination has provided good phylogenetic resolution at both shallow and deep levels in previous work on grasses [START_REF] Gpwg Ii | New grass phylogeny resolves deep evolutionary relationships and discovers C4 origins[END_REF]. DNA was extracted from ground herbarium or silica-dried material using the BioSprint 15 DNA Plant Kit (Qiagen Inc.). Markers were PCRamplified, using primers and procedures as described before [START_REF] Gpwg Ii | New grass phylogeny resolves deep evolutionary relationships and discovers C4 origins[END_REF], Taylor et al. 2012), and sequenced with Sanger technology. For some samples, extracted DNA was instead processed with a genome-skimming sequencing procedure on a HiSeq platform that has also been described previously (Besnard et al. 2013). Bases from Sanger-derived chromatographs were assigned in Geneious 8 (Biomatters Ltd., Auckland, New Zealand) and checked manually. Genome-skimming sequence reads were assembled into full chloroplast genomes or contigs containing the three marker genes, depending on sequence quality; see Besnard et al. (2013) for the method followed. All newly produced sequences, listed in Appendix S1, are accessible through GenBank.

Sequence mining from GenBank and alignment

To represent as much of the phylogenetic grass diversity as possible, we retrieved all ndhF, trnK-matK and rbcL sequences available on GenBank (as of August 2015) for each clade and selected the longest sequence with fewest ambiguities for each marker per species or subspecies recognised in the NCBI taxonomy. In the Bambusoideae, where low rates of molecular evolution produced insufficient phylogenetic information, we added sequences for the rps16 and rpl16 introns from GenBank. The thus assembled data were combined with the newly produced sequences, and outgroup sequences were added to each dataset.

Using MAFFT v.7 (http://mafft.cbrc.jp/alignment/server/; Katoh & Standley 2013) with default settings, we first roughly aligned each marker per dataset. Rough Maximum Likelihood (ML) trees produced with RAXML V.8 (Stamatakis 2014) were used to inspect each alignment for sequences in strong conflict between marker sets, or on very long branches, suggesting errors; these were removed or replaced. We only kept accessions represented by at least ndhF or trnK-matK, whichever was more common in each dataset. Thus, all accessions in an alignment had at least one marker in common. We removed several GenBank accessions in the large genera Chusquea, Muhlenbergia, Poa, and Rytidosperma that showed little or no divergence and were mostly represented by a single marker.

Sequences for some specimens collected in Madagascar were removed because they showed no genetic divergence from others on the markers studied although they were sometimes identified as different species morphologically. They are nevertheless available on GenBank. In three cases, potential endemics (Andropogon trichozygus, Hickelia madagascariensis MSV986 and Perotis arenacea) were excluded in favour of a non-endemic relative. This was done to conservatively give less weight to dubious endemics in the analysis of range evolution.

The datasets were then re-aligned, trimmed and manually adjusted. Some ambiguously aligned regions were removed from the trnK-matK alignments (see Table A-II.1). For nomenclature we followed the World Checklist of Selected Plant Families (WCSP, Clayton et al. 2016); in cases where WCSP suggested synonymy but taxa appeared divergent or nonmonophyletic in the tree, we retained the NCBI nomenclature. Final datasets contained between 18 (Brachypodieae) and 516 (Paniceae) accessions, for a total of 1928.

Phylogenetics and dating

We first estimated ML phylogenies for each concatenated dataset per clade in RAXML on the CIPRES web platform (Miller et al. 2012), applying a GTR substitution model and accounting for rate heterogeneity with 25 Gamma rate categories per marker. Clade support was assessed with 1000 bootstrap pseudoreplicates. Joint Bayesian tree and divergence time estimation was then performed in BEAST2 (Bouckaert et al. 2014), using the ML phylogeny as starting tree.

Partitions and substitution models were as described for RAXML but using only four Gamma rate categories; the diversification process was approximated with a Yule model; molecular rate heterogeneity was modelled with a lognormal relaxed clock (Drummond et al., 2006). The choice of the parameter-rich GTR+G substitution model was validated a posteriori by ensuring that substitution rates were well estimated and distinct. First tests estimating also the proportion of invariable sites (+I) led to poor estimates for that additional parameter and thus we did not include it.

Dating priors for a first estimation in BEAST2 were taken from a previous study that had used external angiosperm calibration to estimate divergence times in the Poaceae (Christin et al. 2014). Widely used macrofossils are younger than estimates of Christin et al. (2014) for the respective nodes and thus not very informative as minimum constraints, e.g. Cleistochloa and Distichlis with ca. 14 Ma [START_REF] Dugas | Middle Miocene fossil grasses from Fort Ternan, Kenya[END_REF] or the oldest known grass spikelet from the Paleocene/Eocene boundary [START_REF] Crepet | The earliest remains of grasses in the fossil record[END_REF]. Phytolith fossils suggest older ages but are controversial, see below. Median ages for clades recovered by Christin et al. (2014) were used as mean (µ) for normal age priors on nodes, and the 95% high posterior density (HPD) intervals were used as normal standard deviation (SD) by dividing the difference between upper and lower bound by 4 (see Table A-II.2). For Andropogoneae-Arundinelleae, not represented as a clade in Christin et al. (2014), we used the estimates for the crown of Andropogoneae s.str. and the split from Paspaleae.

We ran three to five MCMC chains with 10 to 50 million iterations, depending on the dataset. In Tracer v.1.6 (Rambaut et al. 2014), we checked that chains had converged and ESS values for all relevant parameters were >200, and we combined independent runs, discarding a 10% burn-in each, in LogCombiner. Age estimates and posterior clade probabilities from the combined estimates were summarised on the Maximum Clade Credibility (MCC) tree for each dataset in TreeAnnotator. Christin et al. (2014) found that calibrating divergences in the Poaceae with controversial phytolith fossils yielded significantly older estimates that appear to contradict some of the assumed major events in grass evolution; they concluded that external and phytolith calibration are best treated as alternative hypotheses until more conclusive evidence becomes available. Consequently, we used phytolith-derived ages from that study as calibration priors in a second BEAST2 analysis, using the MCC trees estimated under the first calibration as starting trees with fixed topology. As estimates of the age of the Madagascan grass flora, we obtained the median ages and 95% HPD intervals for stem and crown of endemic lineages recovered in the MCC trees under both age calibrations. C4 clades were identified based on known C4 genera or the photosynthetic pathway of close species in the case of the polyphyletic genera Brachiaria and Panicum (Osborne et al. 2014). Some taxa have not been analysed for their photosynthetic pathway, but their position within known C3 or C4 clades was well supported. Analysis of range evolution ML analysis of range evolution, implemented in the R package BioGeoBEARS (Matzke 2013), was used to estimate the history of lineage dispersal to and from Madagascar. The large possible state space resulting from the wide distribution ranges of many grasses limited the analyses to eight areas, defined as follows: the Madagascar region, Tropical Africa, Southern Africa, Eurasia plus North Africa, the Indian subcontinent, Southeast Asia plus Australasia, North America, and the Neotropics (see also map inset in Fig. II.5). We chose to combine Madagascar with the smaller West Indian Ocean islands as only four of the taxa included were native to one of the islands but not Madagascar. Presence in each area (ignoring introductions) was scored according to WCSP as of April 2016, and occurrences in Madagascar were cross-checked against the list of Vorontsova et al. (2016). We calculated Vincenty ellipsoid distances between approximate area centres with the R package geosphere (Hijmans 2016) and rescaled them by the smallest distance (see Table S2.5). For each dataset, we used the MCC tree obtained under the external calibration without phytoliths, outgroups removed, to compare four range evolution models: (i) the dispersalextinction-cladogenesis (DEC) model (Ree & Smith, 2008); (ii) a DEC model expanded with j, a relative weight for founder-event speciation (DEC+j; Matzke 2014); (iii) an expanded DEC model scaling dispersal probabilities by distance between areas to power x (DEC+x; Van Dam & Matzke 2016); (iv) a model integrating both j and x (DEC+j+x). As maximum range size, we set the present-day maximum in each lineage (from 3 in Bambusoideae to 8 in several clades; see Table A-II.6). Likelihood optimisation was performed for each model, and convergence was verified with the output of the optimx function from the package of the same name [START_REF] Nash | On best practice optimization methods in R[END_REF]. Model performance was assessed using the Akaike Information Criterion corrected for sample size (AICc), penalising parameter-rich models more strongly for smaller trees.

Panicoideae

A-IV (chapter IV: A metabarcoding method for the analysis of grass endophyte communities in Madagascar)

Figure 2 (

 2 Figure 2 (previous page). Diversity of grasses and their habitats. The examples shown are related to this dissertation.A -Festuca orthophylla occurs in the high Andes of South America. It belongs to the "American II" clade of fine-leaved Loliinae (subfamily Pooideae) that presumably immigrated via dispersal from Eurasia (chapter I). Loliinae are cool-adapted C3 grasses mainly found in the northern hemisphere and are restricted to mountains at tropical latitudes. B -Plateau grassland in the western part of Itremo protected area, Madagascar, dominated by C 4 grasses in Aristidoideae and Panicoideae: Aristida tenuissima (endemic), Loudetia simplex and Schizachyrium sanguineum (red patches). C4 grasses immigrated repeatedly to Madagascar, presumably with the expansion of open habitats beginning in the Late Miocene (chapter II). C -Spiny thicket in arid southwest Madagascar, assumed to be the most ancient biome on the island. It is rich in endemics such as baobabs but also grasses, one of which may be the oldest endemic C 4 grass lineage on the island (Eragrostis chabouisii, Chloridoideae, chapter II). D -Plateau landscape at West Itremo, Madagascar, with open grassland in the foreground, dense gallery forest in the ravine, and open tapia woodland on the hills in the background. Grassland and tapia woodland have similar herbaceous plant communities dominated by C4 grasses, while the forest understorey harbours almost exclusively C3 grasses (chapters II and IV). E -Panicum vohitrense, member of a C3 "Madagascar shade clade" in subfamily Panicoideae that is mainly found in the forest understorey and diversified in Madagascar and nearby West Indian Ocean islands (chapter II). F -Nastus borbonicus, an endemic bamboo (Bambusoideae) from Réunion Island. It belongs to the Hickeliinae, a woody bamboo clade that radiated in the wider Madagascar region and dispersed only once to the African mainland (chapter II). G -Chandrasekharania keralensis (Panicoideae), type specimen at Royal Botanic Gardens, Kew. This monotypic genus and Jansenella form a species-poor tropical C3 lineage mainly found in the Western Ghats of India (chapter III). H -Mountain grassland in Eravikulum National Park, Western Ghats, India. The presence of endemic grazers such as the Nilgiri tahr (pictured) testifies to the old-growth nature of these grasslands. The Western Ghats may have been the origin of a very diverse pantropical C4 grass lineage, Andropogoneae-Arundinelleae (chapter III). I -Brachypodium madagascariense (Pooideae), an endemic C3 grass from the forest understorey in highland Madagascar. It harbours symbiotic fungal endophytes of the genus Epichloë that presumably co-dispersed with their host plant (chapter IV). Image sources: A -Yastay/Wikimedia Commons (CC BY-SA 4.0); F -B.navez/Wikimedia Commons (CC BY-SA 3.0); G -Bord of Trustees, Royal Botanic Gardens, Kew; H -Navaneeth Kishor/Wikimedia Commons (CC BY-SA 3.0); B, C, E and I -Maria S. Vorontsova (with permission); D -author.

Figure 3 .

 3 Figure 3. Relationships in the grass family (Poaceae). Species numbers are given for each subfamily. Subfamilies in which C4 photosynthesis evolved are in black, with the number of independent origins given in square brackets. The scale is in millions of years (under external angiosperm calibration). Agecalibrated phylogeny taken from Christin et al. (2014), all other information fromKellogg (2015). Nomenclature followsSoreng et al. (2015[START_REF] Soreng | A worldwide phylogenetic classification of the Poaceae (Gramineae) II: An update and a comparison of two 2015 classifications[END_REF].

Figure 4 .

 4 Figure 4. Hyphae of Epichloë coenophiala growing as endophyte between cells in leaf tissue of tall fescue, Lolium arundinaceum. Source: Nick Hill/USDA/ Wikimedia Commons (public domain).

  Fig. I.3; Table A-I.2). The estimated slope was more negative (log-scale factors -5.3×10 -4 ± SE 8×10 -5 vs. -3.3×10 -4 SE 4.1×10 -5 ) for range expansion (Fig. I.3b) versus founder-event (Fig. I.3c) dispersal rates under DEC+j+x, indicating a stronger drop-off by distance.

Figure I. 2 .

 2 Figure I.2. Histograms of dispersal counts and rates for broad-leaved (BL, with and without Intermediate) and fine-leaved (FL) Loliinae, inferred through stochastic mapping. The DEC model, not including a distance effect, and a DEC+j+x model scaling dispersal rates by shortest distance were both used for 1000 simulations on tree inferred by Minaya (2015). (a) Global dispersal counts under DEC and DEC+j+x; (b) range expansion rates under DEC and DEC+j+x; and (c) founder-event and total dispersal rates under DEC+j+x.

  Figure I.3.Mean per-route dispersal rates in Loliinae, inferred with biogeographical stochastic mapping, plotted against the shortest distance between respective OAs. The DEC model, not including a distance effect, and a DEC+j+x model, scaling dispersal rates by shortest distance, were both used for 1000 simulations on the phylogenetic tree inferred byMinaya (2015). Dispersal rates were calculated per route, for each direction, for BL (including Intermediate; black) and FL (grey) Loliinae lineages, yielding 264 data points. Quasi-Poisson regression of dispersal rates on shortest distance showed a significant negative relationship for each range evolution model and type of dispersal (regression curve in blue, slope value is log-scale). X-axis shows geographical distance in km. Phenotypic syndrome (broad-vs. fine-leaved) and disjunction type (oceanic vs. terrestrial) had no significant effect on dispersal rates when distance was accounted for. (a) Range expansion rates (DEC); (b) range expansion rates (DEC+j+x); (c) founder-event dispersal rates (DEC+j+x); and (d) total dispersal rates (DEC+j+x). Regression on centre distances showed similar results (Fig. A-I.1, annex).

  ). About half of the Madagascar origin lineages fall in subfamily Panicoideae. The 11 time-calibrated phylogenies are summarised in Fig. II.1 1 .

  II.2). Stem divergence times of most strictly endemic lineages estimation based on external calibration were placed in the Neogene, with the exception of Lecomtella which may already have diverged in the Oligocene (median stem age 22.3 Ma, HPD interval 14.8-30.3 Ma; Fig. II.2). Under phytolith calibration, Lecomtella may have diverged in the Eocene (upper bound 38.4 Ma), and upper bounds for the isolated C4 species Aristida ambongensis and Eragrostis chabouisii marginally fall into the Oligocene (26.6 and 26.3 Ma, respectively). Roughly half of the single endemic species diverged from their non-endemic sister taxon only in the Quaternary according to median stem ages. Median stem ages of the majority of endemic C4 lineages are estimated after the start of the global Miocene grassland expansion, around 8 Ma, under both calibrations (Fig. II.2). Estimated median crown ages of five well-supported endemic C4 clades fall in the Late Miocene to Pliocene (lineages 21, 61, 62, 91, and 93 in Fig. II.2). Among endemic C3 clades, the oldest estimated crown ages fall well in the Miocene and belong to the "Forest Shade Clade" (Panicoideae: Paniceae: Boivinellinae; lineages 41 and 43). Further endemic C3 clades have crown ages in the Late Miocene to Quaternary.

  ). In all but two clades (Brachypodieae and Danthonioideae), models incorporating distance (DEC+j+x and DEC+x) together aggregated >0.99 of AICc weight. The curve of lineage accumulation in the Madagascar region (Fig. II.3) suggests that grass diversity has increased exponentially, largely since around 20 Ma under external calibration. In many of the individual clades, most of the increase occurred very recently, i.e. in the last 5 to 10 Ma. Lineage accumulation curves were almost identical under the baseline DEC model (not shown). Sums of marginal area probabilities for the ancestors of clades from the Madagascar region are highest for Tropical Africa, followed by Southern Africa, and lowest for India (Fig. II.4). They are not correlated with distance to Madagascar, whether tested on the estimates from

Figure II. 1 .

 1 Figure II.1. Summary phylogenetic tree of the Poaceae, showing the 11 clades studied. Maximum Clade Credibility trees from BEAST2 analyses, with median node heights under an external calibration without phytoliths, were grafted on a Poaceae backbone from Christin et al. (2014) for presentation. Lineages native to the Madagascar region in bluish green, endemic lineages in dark orange. The 69 lineages with an estimated origin in the Madagascar region are labelled with dark orange dots. Grey outer circle segments denote C3, black segments C4 taxa (Alloteropsis and Paspaleae are simplified as C4 clades). Two large C3 clades that diversified in the Madagascar region, the Hickeliinae and the "Madagascar shade clade", are labelled.

Figure II. 2 :

 2 Figure II.2: Ages of 96 lineages strictly endemic to the Madagascar region, as inferred through divergence time estimation in BEAST2. C3 lineages (N = 45) in grey, C4 lineages (N = 51) in black. Note that these lineages cluster in 25 C3 and 44 C4 lineages when accounting for estimated origins in the Madagascar region (see text). Dots and thick lines are median ages and 95% High Posterior Density (HPD) intervals under external calibration; triangles and thinner lines are median ages and HPD intervals under calibration with phytolith ages. Dotted lines mark geological epoch boundaries; the dashed line at 8 Ma marks the approximate beginning of the global Miocene grassland expansion (MGE; Edwards et al., 2010). (a) Stem ages. Lineages are numbered left to age bars (see Table A-II.3 in Annex A-II). (b) Crown ages of lineages with more than one species.

Figure II. 3 .

 3 Figure II.3. Grass lineage accumulation in the Madagascar region, for all studied clades combined, as inferred through range evolution analysis. Lineages were counted per 1 Ma time bin (based on external calibration without phytoliths) and weighted by their marginal probability to occur in the Madagascar region.

Figure II. 4 .

 4 Figure II.4. Affinities of the Madagascan grass flora with other biogeographic regions. The map shows the areas defined for analysis of range evolution, including the Madagascar region (circle inset in orange). Bars show the sums of ancestral area probabilities for ancestors of Madagascar lineages inferred with the best-scoring range evolution model for each phylogeny (left bar for each area) and current-day occurrence counts of non-endemic Madagascan species (right bar), with grey and black segments denoting the proportion of C3 and C4 lineages or species, respectively. Both bars are scaled to the relative maximum value. Note that current-day occurrences and estimated historical distribution correlate well except for India and the Neotropics.

  g. McAllister & Miller 2016) as well as other plants endemic to open grassy biomes of Madagascar is needed to this end.

Figure II. 5 (

 5 Figure II.5 (previous page). Time-calibrated phylogeny of the Forest shade clade (Panicoideae: Paniceae: Boivinellinae), with estimated Madagascan origin for a large C3 "Madagascar shade clade". Current distribution (dots left to species labels) and ancestral areas inferred under a DEC+j+x model for selected nodes are shown; the map inset shows the areas defined. The tree was extracted from the Maximum Clade Credibility tree inferred with BEAST2 for Paniceae, with median node heights under external calibration. Solid grey bars are 95% High Posterior Density (HPD) intervals; dotted bars are HPD intervals under a calibration with phytolith ages. Diamonds on branches denote C4 clades (Alloteropsis is simplified as such), asterisks on nodes show a Bayesian posterior support ≥0.95. Strictly endemic lineages are numbered (see Table A-II.3 in Annex A-II).

  The study was devised by G.Besnard and myself. G.B. assembled nuclear data and part of the plastome data. Alexandre Meunier assembled part of the plastome data and performed a first phylogenetic analysis as part of his Master thesis. P.-A. Christin and M. Bianconi shared valuable thoughts on divergence time estimation, on an earlier version of this manuscript, and intermediate results from a nuclear genome analysis (M.B., in preparation). My contribution was the assembly of part of the plastome data and the final analysis.

  Figure III.1. Time-calibrated phylogeny of the core Panicoideae, based on complete plastome coding sequences. Shown is the maximum clade credibility tree from a BEAST2 analysis. Node heights are common ancestor ages; grey bars represent 95% high posterior density intervals. Values at nodes are Bayesian posterior probabilities smaller than 1. Nodes that received weak support with other alignment subsets are indicated. Focal species of this study are highlighted in bold.

-

  a .. n .. i . c .. e .. ae• "':....::........

Figure III. 2 :

 2 Figure III.2: Maximum Likelihood phylogeny of Poaceae phyB sequences. Values at nodes are bootstrap values smaller than 70 from 1000 replicates in RAxML. Larger clades are collapsed, with number of tips indicated. Focal species of this study are highlighted in bold.

Figure III. 3 :

 3 Figure III.3: Maximum Likelihood phylogenies of the nadpme (A) and ppc (B) gene families in Poaceae. Values at nodes are bootstrap values smaller than 70 from 1000 replicates in RAxML. Larger clades are collapsed, with number of tips indicated. Focal species of this study are highlighted in bold.

Fig. III. 4 :

 4 Fig. III.4: Distribution and endemism of major lineages in the core Panicoideae. Shown are species numbers and numbers of endemics per TDWG level 3 botanical region, extracted from the World Catalogue of Selected Plant Families (Clayton et al. 2016). Value ranges are given in numbers of species. The phylogeny as suggested by plastome sequences is shown to the left, with question marks indicating unclear branching order. Species number per lineage is given in brackets.

  Agarwal I. & Ramakrishnan U. (2017): A phylogeny of open-habitat lizards (Squamata: Lacertidae: Ophisops) supports the antiquity of Indian grassy biomes. Journal of Biogeography, 44: 2021-2032. Ali J.R. & Aitchison J.C. (2008): Gondwana to Asia: Plate tectonics, paleogeography and the biological connectivity of the Indian sub-continent from the Middle Jurassic through latest Eocene (166-35 Ma). Earth-Science Reviews, 88: 145-166.

Fig. IV. 1 :

 1 Fig. IV.1: The three sampling regions in central Madagascar. The scale is in kilometres.

  IV.2a). After tag matching, quality filtering and removal of singletons (87.5% of unique reads), 7,347,559 (59%) of the reads, corresponding to 302,150 unique reads, remained (Fig. IV.2b). Only 1.4% of these were identified as fungal OTUs through ecotag (Fig. IV.2b). Per sample, there was a mean of 9,441 reads (without controls), while positive controls (i.e. mock communities) had a mean of 11,751 reads, and the number of reads in negative controls and with unused tag combinations was always below 20 and 35, respectively (Fig. IV.2c).

Figure IV. 2 .

 2 Figure IV.2. Quality and quantity of reads obtained through MiSeq sequencing. (a) refers to the original reads, (b) shows read loss through the filtering steps, and (c) shows the distribution of quality-filtered reads among samples. In (c), AC stands for all samples without controls, MC means mock community, NC negative controls, and UC unused tag combinations.

  Fig. IV.4a-b). Forest grass communities had clearly positive values of NRI and NTI, indicating phylogenetic clustering (Fig. IV.4c-d). NRI values indicate random assembly or slight phylogenetic overdispersion and NTI values random assembly to slight phylogenetic clustering for tapia woodland and grassland communities. NMDS clearly distinguished forest grass communities from grassland and tapia woodland based on original species identification coupled with matK barcodes (Fig. IV.5a).

Figure IV. 3 .

 3 Figure IV.3. Distribution of the 768 samples over grass species and habitats (bars) and regions (circles). Plotted left to the species labels is the phylogeny inferred from chloroplast markers (see chapter II), with branch lengths relative to time. lumped Panicum ambositrense and P. perreri together. Oplismenus split in three clusters which suggested that several samples of O. burmanni and O. flavicomus were misidentified as

  Figure IV.4. Grass species richness and phylogenetic diversity per plot, compared between habitats.

  Figure IV.7. Maximum Likelihood ITS phylogeny of Epichloë, including ITS2 sequences of two OTUs recovered in our dataset (in bold). Values at nodes are bootstrap support values. The scale is in substitutions per site.

Figure IV. 6 .

 6 Figure IV.6. Read number for fungal mock community OTUs. Note that the y axis in (a) and both axes in (b) have a logarithmic scale. Vertical lines in (b) are standard deviations.

Figure A-I. 1 .

 1 Figure A-I.1. Mean per-route dispersal rates in Loliinae, inferred with biogeographical stochastic mapping, plotted against the centre distance between respective OAs. Compare with Fig. I.4, which shows the regression on shortest distances.

Fig

  Fig. A-II.1. Grass lineage accumulation in the Madagascar region per clade, as inferred through ancestral range estimation. Lineages were counted per 1 Myr time bin (based on external calibration without phytoliths) and weighted by their marginal probability to occur in the Madagascar region. Total counts are only shown when the clade has both C3 and C4 lineages and their relative probabilities to occur in the region are non-negligible (i.e., >0.1 over the whole time span). Note that as relative probability weights of lineages vary through time, the accumulation curve is not necessarily monotonous.

Fig

  Fig A-III.1 (continued on next page). Whole plastome Maximum Likelihood phylogenies inferred with RAxML from different alignment subsets. The respective scale is in substitutions per site; values at nodes are bootstrap support values <100. A-C, all taxa; D-F (next page), without Gynerium sagittatum.

FigFig

  Fig A-III.2. phyB Maximum Likelihood phylogeny inferred with RAxML. The scale is in substitutions per site; values at nodes are bootstrap support values <100.

Fig

  Fig A-III.4. nadpme Maximum Likelihood phylogeny inferred with RAxML. The scale is in substitutions per site; values at nodes are bootstrap support values <100.

Fig A-III. 5 (

 5 Fig A-III.5 (continued on next page). ppc Maximum Likelihood phylogeny inferred with RAxML. The scale is in substitutions per site; values at nodes are bootstrap support values <100.

Fig

  Fig A-III.5 (continued).

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Table I .1. Performance

 I of six models of range evolution tested on the Loliinae phylogeny inferred byMinaya (2015), for 12 operational areas and a maximum range size of two.

									Estimated parameters: d, range expansion
	rate; e, extinction rate; j, relative weight for founder-event dispersal at node; x, distance-scaling parameter. P.,
	number of parameters, logL, log(likelihood); AIC, Akaike Information Criterion; wAIC, Akaike weight; BIC,
	Bayesian Information Criterion; wBIC, Schwarz weight.
	Range
	evolution
	model	d	e	j	x	P.	logL	AIC	ΔAIC	wAIC	BIC	ΔBIC	wBIC
	DEC+j+x
	(shortest
	distances) 0.004 <0.001 0.037 -0.227	4 -366.24	740	0	>0.99	753	0	>0.99
	DEC+j+x
	(centre
	distances) 0.009 <0.001 0.067 -0.896	4	-380	768	28	<0.001	780	28 <0.001
	DEC+j	0.003	<0.001	0.024	0	3	-392.73	792	51	<0.001	801	48	<0.001
	DEC+x
	(shortest
	distances)	0.013	0.015	0	-0.212	3	-421.09	848	108	<0.001	858	105	<0.001
	DEC+x
	(centre
	distances) 0.035	0.014	0 -1.176	3	-430.7	867	127	<0.001	877	124 <0.001
	DEC	0.01	0.012	0	0	2 -442.57	889	149	<0.001	895	142 <0.001

Figure I.1 (previous page). Estimated

  ancestral ranges of Loliinae, obtained under the best-performing DEC+j+x model of range evolution for shortest distances between areas computed with BioGeoBEARS, mapped on the time-calibrated phylogenetic tree inferred byMinaya (2015). Posterior probability values are indicated at nodes. Pie charts at nodes represent Maximum Likelihood relative marginal probabilities of ancestral ranges, with their colour legend given at the insert chart (only single areas are coloured; white corresponds to two-area ranges). Letters at basal nodes indicate two-area ranges with the highest marginal probabilities. The upper time scale bar represents million years ago (

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Table II .

 II 1. Summary of Poaceae lineages of the Madagascar region recovered in this study. Strictly endemic lineages contain only taxa endemic to the region. Madagascar origin lineages are those with an origin in the region estimated through range evolution analysis. These contain one or more strictly endemic lineages and can also include non-endemic and non-Madagascan taxa. Tables A-II.3 and A-II.6 in Annex A-II give details about individual strictly endemic and Madagascar origin lineages, respectively.

			Photosynthetic pathway	Subfamily
		Total					Single accessions
			C3	C4	Panicoideae	others
	Strictly endemic	96	45	51	50	46	62
	Madagascar origin	69	25	44	31	38	40

Table III .

 III 1. Estimated ages, in Ma, of major nodes in Panicoideae, based on a Bayesian analysis of plastome coding sequences in BEAST2. Given are the estimated median ages and the 95% high posterior density (HPD) interval.

			95% HPD interval
	Node	median	lower	upper
	Jansenella-Chandrasekharania split	13.65	7.19	20.75
	Jansenella-Chandrasekharania stem	22.55	16.18	29.25
	Arundinelleae crown	17.63	11.86	24.24
	Andropogoneae crown	13.48	9.6	17.86
	Andropogoneae-Arundinelleae split	19.46	13.79	26.04
	Paspaleae crown	24.2	17.5	31.02
	Paniceae crown	23.74	17.07	31.22
	Lecomtella stem	30.23	22.61	38.27
	Gynerium stem	33.19	24.81	41.8
	Panicoideae crown	36.74	27.54	45.99

neglecta sav201 Jansenella gr,1fithiana cG209 Chandrasekharania keralensis vsR54064

  Lasiurus scindicus was always found to be sister to the rest. Arundinelleae was always sister to Andropogoneae but its monophyly was weakly to moderately supported. Chandrasekharania and Jansenella always formed a well supported clade sister to Andropogoneae-Arundinelleae. Reynaudia filiformis was confirmed as sister to the remaining Paspaleae, and Gynerium as sister to the remaining core Panicoideae. The position of Lecomtella varied among the alignment subsets: when only CDS were used, Lecomtella diverged just after Gynerium, with high support, but when the full alignment or an alignment without gaps were used, its divergence was placed after that of Paniceae, with weak support. When Gynerium was excluded, as inBurke et al. (2016),

	Capillipedium venustum
	Bothriochloa a/ta
	lseilema macratherum
	Themeda triandra
	Hyparrhenia subplumosa
	Diheteropogon amplectens
	Sorghastrum nutans
	Eulalia aurea
	Sorghum timorense
	Sorghum bicofor
	Saccharum sp. hybrid
	Miscanthus smensis
	Pogonatherum paniceum fmperata cyfindria
	Kerriochfoa siamensis
	Caix facryma-jobi
	lschaemum afrum
	Eriochrysis faxa
	Andropogon burmanicus
	Pofytoca digitata
	Zea nicaraguensis Zea mays
	Arthraxon prionodes
	Arthraxon microphyllus
	Lasiurus scindicus AN-DJl/78-36
	;: o/t dica
	Arundinella nepafensis Msvaoa
	Arundinella deppeana
	Jansenella Steinchisma fa xa
	Otachyrium versicolor
	Pfagiantha tenella
	Streptostachys ramosa
	Coleataenia prionitis
	Homofepis aturensis
	Paspafum fimbriatum
	Paspafum difatatum
	Paspafum gfaziovii . .
	Streptostachys aspenfo/1a
	Axonopus fissifolius
	lchnanthus pallens
	Reynaudia fi/iformis E1 22oa
	Urochfoa reptans
	Eriochfo a meyeriana
	Megathyrsus maximus
	Mefinis minutiffora Msvaog Setaria itafica
	Paspafidium geminatum Cenchrus americanus
	Whiteochfoa capillipes
	Panicum capillare
	Panicum virgatum
	Thyridofe pis xerophifa
	Dichanthefium acuminatum
	Oplismenus hirtel/us Lasiacis nigra Echinochfoa stagnina
	Amphicarpum muhfenbergianum
	Digitaria gfauca MSV950
	D1gitaria exifis
	Lecomte

III.1, full trees can be found in Fig. A-III.1). In Andropogoneae, several nodes separated by very short branches had weak (i.e. <70) bootstrap support, but Lecomtella was always sister to the rest of the core Panicoideae, but with weak support except for the CDS-only subset (Fig. A-III.1, D-F). Note that the branching order among the g gt G Ch ly r p y h sop h o l g o o a n fo s r e f r ic ruf f at t u a s HFPB96 % i1 t7?c°iJirJ t;; : ':fs

/la madagascariensis Gynerium sagittalum P6-301b

	Tristachya humbertii
	Loudetiopsis kerstingii
	Danthoniopsis dinteri
	Danthoniopsis stocksii RHR54967
	Thysanofaena fatifofia
	Centotheca fappacea Zeugites pittien
	Chasmanthium taxum
	Phragmites austrafis
	Eriacnne stipacea
	Neyraudia reynaudiana
	Danthonia cafifornica Aristida purpurea
	Poa palus/ris
	Bambusa multiplex
	Oryza glaberrima
	Puelia olyriformis
	Pharus fatifolius
	Anomochloa marantoidea

  III.2a,. One copy of the J. neglecta phyB gene was more closely related to the J. griffithiana phyB sequence than to the other copy from the same genome. Lecomtella madagascariensis diverged after Paniceae but with weak bootstrap support. The two phyB copies of Gy. sagittatum successively branched at the base of the core Panicoideae, one clustering with a Gynerium phyB sequence from GenBank (EU272433.1). Panicoideae was not monophyletic, and relationships within Panicoideae tribes and among PACMAD subfamilies differed strongly from the plastome topology. The ITS tree recovered the main lineages of the Panicoideae, but placed Gy.

sagittatum with outlying Panicoideae and Le. madagascariensis with Paniceae and Paspaleae (Figs III.2b, A-III.3). Chandrasekharania and Jansenella form a strongly supported clade with Andropogoneae, Arundinella and Garnotia but are paraphyletic at its base, with weak support. Arundinella and Garnotia successively diverge next.

  Besnard and myself. M. S. Vorontsova and H. Ralimanana helped with the selection of sample sites and the identification of grass species (M.S.V.). H. Andrianirina and J. Razanatsoa helped with sampling in the field. G.B. collected samples in the field and amplified and sequenced matK grass barcodes.

S. Manzi prepared libraries for sequencing. My contribution was field sampling, DNA extraction, PCR with fungal primers and data analysis. Grass community data from nine plots sampled here have been included in a study entitled "Grass traits and species composition differentiate tapia woodlands from forest in Madagascar", authored by C.L. Solofondranohatra, M.S. Vorontsova, J. Hackel, G. Besnard, S. Cable, V. Jeannoda and C.E.R. Lehmann and submitted to Frontiers in Ecology and Evolution in October 2017.

Table A -

 A I.1. Distances used for DEC+x and DEC+j+x models in BioGeoBEARS. They were calculated by locating approximately the centre points of or shortest-distance points between Operational Areas on a world map and then calculating Vincenty ellipsoid distances from them. Distances are here given in km but were normalised to the respective smallest value for the analysis to avoid parameter scaling problems in BioGeoBEARS optimisation. Note that for shortest distance, the distance between contiguous regions was set to a very small value (0.01 of the smallest distance) as the distance scaling parameter x requires non-zero values.

	Shortest distances
		A	B	C	D	E	F	G	H	I	J	K	L
	A	0
	B	1177
	C	1515		0
	D	6314		1927	0
	E	6108		1083	0	0
	F	8118		3392	0	0	0
	G	10404		10406	13251	6038	3367	0
	H	10677		9563	3458	6779	94	10227	0
	I	7620		7868	6858	10046	6974	10582	0	0
	J	6389		6857	7222	9669	9442	8634	3494	0	0
	K	6139		3626	109	3691	1959	17581	1950	5128	5506	0
	L	18692		16933	12613	13254	11394	6060	4191	8434	10717	11247	0
	Centre distances
		A	B	C	D	E	F	G	H	I	J	K	L
	A	0
	B	2514
	C	3134		0
	D	7633		4621	0
	E	7840		5186	4356	0
	F	10939		8165	5600	3100	0
	G	11836		13703	16282	11929	11142	0
	H	14787		12974	8801	11632	9507	13245	0
	I	10390		11071	10155	14509	14473	13608	5891	0
	J	8206		9883	10951	14732	16391	12489	8696	2808	0
	K	7835		5810	3209	7550	8488	19444	7230	6961	7920	0
	L	19262		17603	13111	12763	9673	7625	5682	9572	11536	12776	0

Table A -

 A I.2. Statistics of quasi-Poisson regression of per-route dispersal rates, estimated through stochastic mapping under two range evolution models (DEC and DEC+j+x with shortest distances), on distance, disjunction type, and phenotypic syndrome, and their interactions. Regression models 1-4 use shortest distances between Operational Areas (OAs) as predictor, models 5-8 instead use distances between approximate centres of OAs. Disjunction type is terrestrial (T) or oceanic, Phenotypic syndrome is fine-leaved (FL) or broad-leaved (including intermediate). Significant variables (p < 0.05) are highlighted in bold. Coefficient estimates are logscale.

	Coefficient	Estimate	SE	t	p value
	1: Range expansion rate -null deviance 0.13 (263 df), residual deviance 0.08 (256 df), dispersion 0.0004
	Intercept	-7.74227 0.31327 -24.71	<0.001
	Phenotypic syndrome (FL)	0.03174	0.4348	0.07	0.942
	Disjunction type (T)	0.72555	0.3686	1.97	0.05
	Shortest distance	-0.00027 0.00006	-4.48	<0.001
	Phenotypic syndrome (FL) : Disjunction type (T)	-0.63194 0.54152	-1.17	0.244
	Phenotypic syndrome (FL) : Shortest distance	0.00002 0.00008	0.26	0.798
	Disjunction type (T) : Shortest distance	-0.00009 0.00013	-0.69	0.491
	Phenotypic syndrome (FL) : Disjunction type (T) : Shortest distance	0.00006 0.00019	0.31	0.755
	1b: Range expansion rate -null deviance 0.13 (263 df), residual deviance 0.08 (262 df), dispersion 0.00042
	Intercept	-7.43967 0.12953 -57.44	<0.001
	Shortest distance	-0.0003 0.00003	-8.88	<0.001
	2: Range expansion rate -null deviance 0.08 (263 df), residual deviance 0.04 (256 df), dispersion 0.00034
	Intercept	-8.18359 0.45841 -17.85	<0.001
	Phenotypic syndrome (FL)	0.10299 0.60581	0.17	0.865
	Disjunction type (T)	0.57749 0.52245	1.11	0.27
	Shortest distance	-0.00061 0.00018	-3.29	0.001
	Phenotypic syndrome (FL) : Disjunction type (T)	-0.78545 0.74403	-1.06	0.292
	Phenotypic syndrome (FL) : Shortest distance	0.00017 0.00021	0.8	0.425
	Disjunction type (T) : Shortest distance	0.00006 0.00028	0.21	0.834
	Phenotypic syndrome (FL) : Disjunction type (T) : Shortest distance	-0.00015 0.00041	-0.38	0.707
	2b: Range expansion rate -null deviance 0.08 (263 df), residual deviance 0.04 (262 df), dispersion 0.00037
	Intercept	-7.97621	0.1746 -45.68	<0.001
	Shortest distance	-0.00053 0.00008	-6.55	<0.001
	3: Founder-event dispersal rate -null deviance 0.11 (263 df), residual deviance 0.06 (256 df), dispersion 0.00041
	Intercept	-7.80806 0.33987 -22.97	<0.001
	Phenotypic syndrome (FL)	-0.32361 0.50485	-0.64	0.522
	Disjunction type (T)	0.53648 0.40922	1.31	0.191
	Shortest distance	-0.0003 0.00007	-4.32	<0.001
	Phenotypic syndrome (FL) : Disjunction type (T)	0.0656 0.61027	0.11	0.914
	Phenotypic syndrome (FL) : Shortest distance	0.00007	0.0001	0.68	0.497
	Disjunction type (T) : Shortest distance	-0.00015 0.00017	-0.88	0.382
	Phenotypic syndrome (FL) : Disjunction type (T) : Shortest distance	0.00001 0.00024	0.02	0.982
	3b: Founder-event dispersal rate -null deviance 0.11 (263 df), residual deviance 0.07 (262 df), dispersion 0.00043
	Intercept	-7.60978 0.14563 -52.26	<0.001
	Shortest distance	-0.00033 0.00004	-8.03	<0.001
	4: Total dispersal rate -null deviance 0.16 (263 df), residual deviance 0.08 (256 df), dispersion 0.00052
	Intercept	-7.34525 0.31835 -23.07	<0.001
	Phenotypic syndrome (FL)	-0.11645 0.45151	-0.26	0.797
	Disjunction type (T)	0.61262	0.3746	1.64	0.103
	Shortest distance	-0.00036 0.00007	-4.81	<0.001
	Phenotypic syndrome (FL) : Disjunction type (T)	-0.29872 0.54828	-0.54	0.586
	Phenotypic syndrome (FL) : Shortest distance	0.00006	0.0001	0.61	0.541
	Disjunction type (T) : Shortest distance	-0.00013 0.00016	-0.81	0.417
	Phenotypic syndrome (FL) : Disjunction type (T) : Shortest distance	0.00001 0.00024	0.03	0.973

4b: Total dispersal rate -null deviance 0.16 (263 df), residual deviance 0.08 (262 df), dispersion 0.00054

Table A -

 A II.1. Ambiguously aligned regions that were removed from the trnK-matK alignments.

	Clade	Position in alignment	Length (bp)	Type
	Andropogoneae-Arundinelleae	155	32	poly-T
		245	9	poly-A
		426	11	poly-T
	Aristidoideae	76	14	poly-T
	Arundinoideae-Micrairoideae	83	16	poly-T
		298	8	poly-T
	Bambusoideae	409	19	poly-T
	Chloridoideae	320	13	poly-T
		520	22	poly-T
		2600	14	poly-AAAT
		2628	15	poly-A
	Danthonioideae	353	23	poly-T
		530	10	poly-T
	Oryzoideae	348	13	poly-T
		2362	78	longer repeated motif
	Panicoideae	76	19	poly-T
	Paniceae	104	33	poly-T
		320	14	poly-T
		2638	63	ambiguous region

Table A -

 A II.2. Calibrated nodes and age priors (in Ma) used (taken from Christin et al. 2015).

	Node	Calibration 1 (external, without phytoliths)	Calibration 2 (with phytoliths)
		µ	SD	µ	SD
	Andropogoneae crown	11.792	2.9555	14.45	3.383
	Andropogoneae-Paspaleae split	28.502	3.335	34.296	3.7335
	Aristidoideae crown	32.59	6.034	41.532	7.7445
	Arundinoideae-Micrairoideae split	38.518	5.1265	47.506	6.9835
	Bambusoideae crown	28.376	7.0585	34.208	9.0975
	Brachypodieae divergence	34.218	3.33	43.712	4.2565
	Chloridoideae crown	38.532	3.6305	49.116	4.359
	Danthonioideae crown	29.242	4.6135	38.732	6.4875
	Oryzoideae crown	38.548	6.126	67.99	0.941
	Panicoideae crown	38.188	3.8605	48.096	4.9415
	Paniceae crown	25.46	2.767	30.74	2.971
	Poeae crown	26.588	2.8435	32.296	3.636

Table A -

 A II.3. Lineages strictly endemic to the Madagascar region, recovered through phylogenetic analysis. Photosynthetic pathway, median stem age under external calibration (cal. 1) and calibration with phytoliths (cal. 2), tip number, and an estimate of true species richness are given.

		Annex
	No. Clade No. Clade	Tips Tips	Photos. pathway Photos. pathway	Median stem age (Ma) Median stem age (Ma)	No. of tips No. of tips	Estimated species richness Estimated species richness
	No. Clade 30 Paniceae 62 Paniceae 31 Paniceae 63 Andropogoneae-	Sacciolepis viguieri RGD190 Setaria scottii MSV1041, Setaria madecassa Tips Poecilostachys bakeri MSV301, Poecilostachys MSV979, Setaria vatkeana MSV1813 sp. MSV492, Poecilostachys sp. RCH65, Chrysopogon humbertianus MSV1413	Photos. pathway C3 C4 C3 C4	Median stem age (Ma) Cal. 1 Cal. 2 Cal. 1 Cal. 2 3.03 3.76 11.06 13.87 Cal. 1 3.95 4.99 Cal. 2 0.27 0.32	No. of tips 1 3 11 1	Estimated species richness
	Arundinelleae	Poecilostachys gougerotiana RH1639,
	1 Oryzoideae 2 Oryzoideae 3 Oryzoideae 4 Bambusoideae Hickelia madagascariensis Leersia perrieri, Leersia perrieri HPB17323 Maltebrunia leersioides GES3926 Humbertochloa bambusiuscula MSV956 Poecilostachys hildebrandtii RCH04, 64 Andropogoneae-Andropogon andringitrensis MSV1260 Poecilostachys geminata RCH05, Poecilostachys Arundinelleae bromoides, Oplismenus flavicomus RCH25, 65 Andropogoneae-Elionurus tristis MSV589 Poecilostachys festucacea RCH30, Oplismenus flavicomus MSV737, Poecilostachys bakeri Arundinelleae 5 Bambusoideae Hickelia madagascariensis MSV724, Hickelia LRK2035 66 Andropogoneae-Andropogon ibityensis MSV754 32 Paniceae Panicum ambositrense MSV736, Panicum perrieri Arundinelleae madagascariensis MSV731 6 Bambusoideae Arundinaria sp. MSV723, Arundinaria MSV749 67 Andropogoneae-Arthraxon antsirabensis NOP217 33 Paniceae Acroceras ivohibense MSV1222 Arundinelleae marojejyensis MSV487, Arundinaria humbertii MSV1223 7 Bambusoideae Hitchcockella baronii DR and TA 3430, Sokinochloa chapelieri MSV319, Sokinochloa australis LRK780, Sokinochloa brachyclada SD1352, Cephalostachyum chapelieri MSV499, Perrierbambus sp. MSV1321, Perrierbambus madagascariensis TRS2665, Valiha diffusa MSV1487, Sirochloa parvifolia NOP224, 34 Paniceae Brachiaria antsirabensis AJL1038, Brachiaria 68 Andropogoneae-Ischaemum koleostachys MSV1299, Ischaemum Arundinelleae koleostachys dimorpha HH3879 35 Paniceae Panicum lycopodioides GB04-2013, Brachiaria 69 Andropogoneae-Andropogon itremoensis MSV753 Arundinelleae epacridifolia MSV722, Brachiaria dimorpha 70 Andropogoneae-Saccharum hildebrandtii MSV739, Saccharum MSV1234 36 Paniceae Oplismenus sp. MSV1468 Arundinelleae perrieri NOP140 37 Paniceae Panicum subhystrix MSV748 71 Andropogoneae-Saccharum viguieri MSV1248, Saccharum Arundinelleae hildebrandtii LRK2008 Decaryochloa diadelpha SD1116, Nastus borbonicus, Nastus cf. perrieri MSV495, Nastus 38 Paniceae Cyrtococcum deltoideum RCH10, Cyrtococcum 72 Andropogoneae-Dimeria manongarivensis MSV343 bosseri NOP228 Arundinelleae aristatus LG2683, Nastus elongatus MSV309 8 Brachypodieae Brachypodium perrieri MSV1242 39 Paniceae Pseudolasiacis leptolomoides MSV983 73 Arundinoideae-Isachne muscicola MSV597, Isachne humbertiana 9 Brachypodieae Brachypodium madagascariense MSV735, 40 Paniceae Brachiaria tsiafajavonensis MSV697 Micrairoideae MSV496 41 Paniceae Brachiaria fragrans P06769493, Panicum ibitense 74 Arundinoideae-Isachne humicola MSV563 Brachypodium perrieri MSV616, Brachypodium RGD171, Panicum spergulifolium MSV1250, Micrairoideae perrieri LRK2010 10 Poeae Festuca borbonica GB03-2013 cupressifolium MSV1233, Panicum andringitrense Micrairoideae Panicum sp. nov. MSV1218, Panicum 75 Arundinoideae-Styppeiochloa hitchcockii MSV993	C3 C3 C3 C3 C4 C4 C3 C4 C3 C3 C4 C3 C3 C3 C4 C3 C4 C4 C3 C3 C4 C3 C4 C3 C3 C3 C3 C3 C3 C3 C3 C3	1.4 2.82 3.19 0.45 0.34 0.93 1.03 1.43 2.75 2.65 1.1 3.87 6.01 4.58 1.72 4.93 2.27 2.62 5.49 5.77 3.07 6.64 5.1 2.58 7.39 1.13 5.07 6.73 10.7 1.9 0.64 7.21	2.52 5.06 5.94 0.55 0.42 1.16 1.32 1.77 3.44 3.11 1.39 4.46 7.34 5.45 2.09 5.90 2.83 3.28 6.76 7.72 3.86 7.87 6.15 3.22 9.34 1.36 6.06 8.62 13.05 2.29 0.77 8.44	2 1 1 1 1 1 1 2 2 1 3 1 14 2 2 1 3 2 1 2 1 2 1 1 2 1 1 3 7 1 1 1
	11 Poeae 42 Paniceae Micrairoideae 76 Arundinoideae-	Agrostis elliotii LRK2033, Agrostis elliotii Chasechloa madagascariensis HPB103, MSV1037 MSV591, Brachiaria bemarivensis MSV936 Styppeiochloa sp. MSV1306	C3 C3 C3	11.74 1.31 10.48	14.21 1.57 12.40	2 2 1
	12 Poeae 77 Chloridoideae	Poa perrieri MSV1232 Chasechloa egregia LHB s.n. Eragrostis capuronii NOP186	C3 C4	1.44 0.28	1.62 0.34	1 1
	13 Poeae 14 Poeae 43 Paniceae 78 Chloridoideae 79 Chloridoideae 15 Poeae 44 Paniceae 16 Poeae 45 Paniceae 80 Chloridoideae 17 Poeae 46 Paniceae 81 Chloridoideae 18 Aristidoideae 47 Paniceae 82 Chloridoideae 19 Aristidoideae 48 Paniceae 83 Chloridoideae 49 Paniceae 84 Chloridoideae 20 Aristidoideae 50 Paniceae 85 Chloridoideae	Agrostis sp. MSV1846 Festuca camusiana LRK2032, Festuca camusiana Acroceras cf. boivinii LRK2014, Acroceras boivinii Eragrostis lateritica MSV638 MSV985, Acroceras tenuicaule RCH61, Acroceras sp. nov. MSV1379, Acroceras calcicola NOP215 Eragrostis cf. bemarivensis MSV923, Eragrostis MSV617, Festuca perrieri NOP85 Anthoxanthum madagascariense MSV613 Thuarea perrieri MBV and AMT 1534 hildebrandtii MSV590 Agrostis emirnensis MSV600 Eriochloa subulifera MSV351 Lepturus cf. humbertianus MSV1403 Pseudobromus breviligulatus MSV725 Brachiaria pseudodichotoma MSV942 Eragrostis betsileensis MSV1002 Sartidia perrieri HPB10751 Panicum mahafalense GMP14929 Neostapfiella perrieri JB20177 Sartidia isaloensis PM3609, Sartidia isaloensis Brachiaria subrostrata MSV716 Eragrostis boinensis MSV935 Pennisetum pseudotriticoides MSV718 Chloris humbertiana NOP206 MSV1325 Aristida tenuissima MSV1053 Digitaria glauca MSV950 Lepturus anadabolavensis NOP203	C3 C3 C3 C4 C4 C3 C4 C3 C4 C4 C3 C4 C4 C3 C4 C4 C3 C4 C4 C4 C4 C4 C4 C4	2.18 2.96 13.21 0.61 0.97 2.14 0.28 3.77 0.34 1.03 5.44 0.33 1.04 1.73 0.9 1.43 3.29 1.32 2.67 1.77 3.48 1.37 2.24 3.9	2.58 3.58 16.00 0.77 1.35 2.53 0.35 4.40 0.45 1.30 6.73 0.45 1.29 2.32 1.08 1.84 4.04 1.73 3.20 2.47 4.32 1.69 2.74 4.89	1 5 1 3 2 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1
	21 Aristidoideae 51 Paniceae 86 Chloridoideae	Aristida similis P02260258, Aristida similis Setaria bathiei RGD196 Eragrostis humbertii MSV1417	C4 C4 C4	8.41 1.79 4.46	10.54 2.17 5.73	6 1 1
	52 Paniceae 87 Chloridoideae 53 Paniceae 88 Chloridoideae	LRK2006, Aristida rufescens MSV586, Aristida Cenchrus cafer Decaryella madagascariensis TBC31391, Decaryella madagascariensis MSV1398 rufescens MSV337, Aristida rufescens MSV333, Aristida cf. similis MSV346 Digitaria ankaratrensis MSV1044 Dactyloctenium capitatum MSV1393	C4 C4 C4 C4	2.81 3.61 2.98 6.29	3.31 5.20 3.76 7.98	2 1 1 1
	22 Aristidoideae 55 Paniceae 54 Paniceae 89 Chloridoideae	Aristida ambongensis MPG17367, Aristida Stenotaphrum unilaterale MSV1043 MSV1772 ambongensis RNF2144 Brachiaria pseudodichotoma PBP3180 Neostapfiella sp. MSV1486, Neostapfiella sp.	C4 C4 C4 C4	3.71 12.49 1.4 6.51	4.37 17.13 1.14 7.96	1 2 1 2
	23 Panicoideae 56 Paniceae 90 Chloridoideae	Lecomtella madagascariensis Panicum vohitrense MSV1466 Eragrostis stolonifera MSV1046	C3 C4 C4	22.34 4.1 6.86	28.27 5.46 8.24	1 1 1
	24 Panicoideae 57 Paniceae 91 Chloridoideae 25 Paniceae 58 Paniceae 92 Chloridoideae 26 Paniceae 59 Paniceae 93 Chloridoideae 27 Paniceae 60 Paniceae 61 Paniceae 94 Chloridoideae 28 Paniceae 95 Danthonioideae Merxmuellera ambalavaoensis MSV1235, Tristachya humbertii MSV1369, Tristachya Brachiaria humbertiana MSV1378, Brachiaria cf. Acrachne perrieri AJML13867, Acrachne sp. betsileensis MSV1003, Danthoniopsis isalensis humbertiana MSV646 MSV1767 MSV1370 Cyrtococcum tamatavense RCH39 Yvesia madagascariensis MSV957 Viguierella madagascariensis MSV966 Panicum aff. vohitrense MSV1847 Setaria humbertiana MSV1414 Sporobolus perrieri MSV1415, Sporobolus sp. Brachiaria sp. nov. MSV387, Brachiaria sp. nov. Stenotaphrum oostachyum MSV1042 AA156, Sporobolus halophilus MSV585 Panicum cf. voeltzkowii CF, Panicum voeltzkowii Eragrostis chabouisii NOP185 RCH43 Panicum malacotrichum RCH19 MSV1027, Panicum cinctum MSV1038, Panicum Merxmuellera tsaratananensis MSV486 EUR27, Panicum sp. GLO19, Panicum cinctum	C4 C4 C4 C3 C4 C4 C3 C4 C4 C3 C4 C4 C4 C3 C3	5.23 5.7 6.47 0.3 6.41 6.96 0.31 7.3 9.21 0.83 7.16 10.3 16.25 1.21 1.42	6.47 7.46 7.98 0.36 8.36 9.55 0.37 8.45 11.74 1.08 8.04 12.60 20.22 1.55 1.81	3 2 2 1 1 1 1 3 1 1 2 1 8 1 2
	29 Paniceae 96 Danthonioideae Pentameris andringitrensis MSV1229 Cyphochlaena madagascariensis, Cyphochlaena cf. voeltzkowii MSV937, Panicum luridum	C3 C3	3.3 5.64	4.09 7.46	2 1
		madagascariensis MSV954 MSV741, Panicum luridum MSV909

Table A -

 A II.4. Areas defined for range evolution analysis, approximate geographical centres, and Vincenty ellipsoid distances between area centres, scaled by the smallest distance.

		Area	Appr. centre	Vincenty ellipsoid distance to area centre (relative)
	Code	Description	Lat. Long.	E	W	I	S	U	M	O	F
	E	Eurasia and North Africa	49.8	80.5	0
	W	West Indian Ocean (incl.	-18.4	47.1	3.22	0
		Madagascar)
	I	Indian Subcontinent	21.6	78.8	1.23	2.20	0
	S	Southern Africa	-25.5	23.5	3.93	1	3.10	0
	U	Southeast Asia and Australasia	-1.81	126	2.81	3.43	2.25	4.37	0
	M	North America	43.6 -102.1	3.78	6.26	5.00	5.77	5.24	0
	O	Neotropics	-13.4 -61.1	5.74	4.46	6.14	3.46	7.10	2.96	0
	F	Tropical Africa	3.5	24.8	2.86	1.35	2.41	1.26	4.41	4.92	3.78	0

Table A -

 A IV.1. OTUs based on 97% ITS2 identity and with >25 reads per sample, identified as fungal with ecotag and the UNITE database. Only OTUs present in more than one sample (and a conspicuously abundant OTU, no. 17) were additionally submitted to BLAST searches against GenBank.

		No. of		No. of			Best
	OTU	samples	UNITE taxon	reads	GenBank taxon	Potential ecology	match Identity
	1			1379	Phoma/Epicoccum	pathogen/endophyte	KT310093	100
						saprophyte/endophyte
	2		Capnodiales	486	Toxicocladosporium	(tropical)	KF777190	99.7
	3			552	Cladosporium sp. saprophyte/pathogen KU986780	100
	4			476	?		MF569901	97.1
	5			593	?		MF568876	95.3
	6			334	Ramichloridium sp. saprophyte/pathogen KM357331	98.7
	7		Capnodiales	241	Capnodiales		KY228722	97.3
			Hypocreales:
	8		Clavicipitaceae	181	Epichloë sp.	endophyte	KC881085	97.3
	9			361	Septoria sp.	pathogen MF569709	97.6
	10		Capnodiales	143	?		KF435160	98
	11			359	?		KJ869155	96.7
	12			169	Sordariomycetes		EU002898	97.7
	13			229	?		JF951143	93
	14			358	?		MF569334	94
	15			76 Arthrobotrys/Microdochium	pathogen KP689198	100
	16			115	?		KF436353	95.7
	17			4766	Festuca (grass)
			Hypocreales:
	18		Clavicipitaceae	367
	19			836
	20			228
	21			207
	22			182
	23			187
			Pleosporales:
			Paraphaeosphaeria
	24		michotii	162
	25			97
	26			70
	27			205
	28			70
	29			70
	30			60
	31			72
	32			57
	33			85
	34			108
	35			236
	36			29
	37			47
	38

This chapter was accepted for publication in Journal of Biogeography, pending final corrections and in slightly different format, in October

2017, under the title "Grass diversification in Madagascar: in situ radiation of two large C3 shade clades and support for a Miocene to Pliocene origin of C4 grassy biomes", co-authored by J. Hackel, M. S. Vorontsova, O. P. Nanjarisoa, R. C. Hall, J. Razanatsoa, P. Malakasi and G. Besnard. G.B., M.S.V., and myself devised the study. M.S.V., O.P.N., R.C.H. and G.B. collected samples. G.B. and P.M. produced molecular data. My contribution was the phylogenetic and biogeographic analysis and the writing of the manuscript.

Sequence data were submitted to GenBank. The accession numbers of these new sequences, along with voucher information, as well as those of the accessions retrieved from GenBank have not been included in the annex of this dissertation as the table is very large (>1,900 rows). They will be available with the online article as supplementary information.

Acknowledgements

I would like to thank a number of people for accompanying me through these last three years.

contract funded by the French Government and through other public funds, including from two "Labex" (CEBA, ANR-10-LABX-25-01 and TULIP, ANR-10-LABX-0041) and an Idex UNITI student mobility grant for fieldwork in Madagascar (RECAC15EX110). The last two years in Europe and the world reminded me that the freedom of students and academics to move and exchange is far from a given and I am grateful for the opportunity to study and work in France.

We obtained the ages of clades estimated as occurring in the Madagascar region with marginal probability >0.5 under the best-performing model for each phylogeny. As an estimate of the relative historical importance of each defined area as source area for dispersal to Madagascar, we summed the relative likelihoods for nodes that were direct ancestors to a node estimated present in the Madagascar region. This sum thus incorporates both the number of clades for which dispersal is likely, and the likelihood of each area being the ancestral area of those clades. We then tested for correlation of these estimates with distance to Madagascar. To compare estimated historical dispersal with current distribution patterns, we also correlated the occurence counts of species native but not endemic to Madagascar (excluding other West Indian Ocean islands, based on checklist from Vorontsova et al., 2016) in each of the defined areas, as per WCSP, with distance to Madagascar. Finally, we traced the accumulation of C3 and C4 grass lineages in the Madagascar region with a lineage-through-time analysis: using MCC trees with median ages under external age calibration, we counted the number of C3 and C4 lineages in each 1 Myr time bin and weighted them by their marginal probability (under the best range evolution model) to occur in the Madagascar region. Multiple accessions per species were counted as a singe lineage when monophyletic. In the case of multiple accessions that did not form a single clade, we only counted the accession collected in the Madagascar region.