Peter Convey

Frédérique Viard

Patricia Gibert

Joan Van Baaren

David Siaussat

Eric Petit

Mathieu Laparie

Jean-Marc Pallisson

Bertrand Je

Marc Maryvonne

Aude, Cendrine, Françoise, Andreas, Cécile, Pascaline Claudia Christophe

Benoit, Hector… Benj Amin

Denis

Julien Liliane Dennis

Jeremy Stephen

Miguel Un

Marc Et Poplicorne

Christophe Mr Popeleph

Francesco Gilles

Caro Les Renker

Dédé Sarah

Qui

Nico Mcgyver

Prout Eker

Tata Jéj

Gilles

Jean-Pierre Thomas

Laureline, Hélène, Yves Tessa Agnès

Marc Salomé

Quentin Popmoule

Lisa

Flore

Diana

Sarah

Alix Gorenka

Kévin, Bastien Nathan

Chaton

Beubeu Thib'

JB Jenny Pierraf Eu

T Ouisse

M Lebouvier

D Renault

D Bonte

F Hendrickx

M Soledadinus

l'équipe des plonplongeurs du programme

Keywords: Insect distribution, sampling, rearing conditions, and experimental

de t hèse. I warmly t hank bot h of my supervisors, David and Frederik, f or all t heir support and guidance during t hese 3 years, and f or t heir availabilit y despit e t heir f ully booked schedules. I f elt really saf e, bet ween you t wo, t o t ake my f irst st eps int o t his scient if ic career. Merci à

Table of Contents

-Discussion

-Conclusion

Chapter 5 -Effects of elevation on the physiology of the invasive carabid beetle Merizodus soledadinus at the Kerguelen Islands

General Introduction

-Biological invasions and associated concepts

The distributional ranges of many species fluctuates naturally on a time scale of centuries to years, linked with alterations in climate or biological interactions. Human-mediated transportation and introduction of propagules outside of their natural biogeographic range have increased the opportunities for plants and animals to cross geographic boundaries by orders of magnitude [START_REF] Brown | An Essay on Some Topics Concerning Invasive Species[END_REF][START_REF] Lockwood | The role of propagule pressure in explaining species invasions[END_REF]. In particular, since the industrial revolution and the demographic explosion of human population, global trade accelerated this phenomena, by multiplying the vectors of transportation among distant regions. This has resulted in increasing number of examples of newly arrived species becoming dominant in the introduced community (Mack et al., 2000;Bax et al., 2003;Roy et al., 2011), expanding geographic ranges (Simmons & Thomas, 2004;[START_REF] Burton | Trade-offs and the evolution of life-histories during range expansion[END_REF]White et al., 2012), and impacting autochthonous communities (Hejda et al., 2009;Vilà et al., 2011). Biological invasions are now recognized as a major threat to biodiversity alongside with global climate change, habitat fragmentation and modification of land use, and greatly participate to biotic homogenization [START_REF] Lodge | Biological invasions: Lessons for ecology[END_REF]Vitousek et al., 1996;Dukes & Mooney, 1999;McKinney & Lockwood, 1999;Millenium Ecosystem Assessment, 2005;Simberloff et al., 2013).

Biological invasions received a growing interest from biologists over the past decades (at the instigation of the SCOPE program in 1982), and constitute now a research field per se. Different aspects of invasions are currently investigated, with different objectives. Studies for conservation purpose have been intensively developed, to understand how invasive species can be managed, but they also are associated to other research fields because they constitute natural experiments ideal to study ecological and evolutionary processes in real time, like fast-growing populations, shifts among ecological niches, and accelerating expanding ranges (Sax et al., 2007;Davis, 2009).

Literature related to biological invasions extensively reported invasion cases. This overwhelming number of studies greatly varies in scopes and methods, depending on the main research question asked (impacts on native population and ecosystem, comparison among introduced and source populations, population dynamics, reasons underlying invasive success, etc…) and on the taxa studied (plant, or animal, terrestrial or aquatic, sessile or motile, predator or phytophagous). This profusion of studies led to parallel and confusing development of concepts and terminology related to biological invasions (reviewed in Falk-Petersen et al., 2006;Valéry et al., 2008;Catford et al., 2009;Van Kleunen et al., 2010;[START_REF] Blackburn | A proposed unified framework for biological invasions[END_REF]Gurevitch et al., 2011). As a result, most of studies related to biological invasions specify which definition of invasive species they use. This confusion may also partly result from the human perception of non-native, introduced, alien, established, invasive species (Larson, 2005;Tassin & Kull, 2015), often considered as being bad . Yet, during the last decade, several unified frameworks have been proposed to better describe biological invasion processes and further species with quite precision, and to assess transport vectors (Estoup & Guillemaud, 2010;Cristescu, 2015). Associated with historical knowledge (if available), these techniques constitute a powerful tool enabling to better understand invasive populations origins, and allow subsequent comparisons between source and introduced populations to further test eco-evolutionary hypotheses.

Invasive populations are generally thought to be founded by a small number of individuals (Dlugosch & Parker, 2008), representing a more or less reduced fraction of the pool of genetic diversity of the source population (Nei et al., 1975;Barrett et al., 1990), and probably high inbreeding levels in introduced populations (van [START_REF] Van Buskirk | The change in quantitative genetic variation with inbreeding[END_REF]. Genetic diversity is the basis of the adaptive potential of populations to adapt to new environmental conditions (Fisher, 1930). From these two assumptions emerges the Genetic Paradox of Invasions (GPI): how invasive populations manage to adapt to the novel selective pressures encountered in the introduced area despite reduced genetic diversity (Sax & Brown, 2000)? In this context, genetic analyses of invasive populations first focused on comparing levels of genetic diversity between native and introduced populations [START_REF] Lee | Evolutionary genetics of invasive species[END_REF]Cox, 2004;[START_REF] Bossdorf | Phenotypic and genetic differentiation between native and introduced plant populations[END_REF]Novak & Mack, 2005;Wares et al., 2005;Dlugosch & Parker, 2008) and found contrasted outcomes. Many authors showed decreased levels of genetic diversity in the introduced population compared with the native populations, and cases with increased genetic variation in the invasive population were likely due to admixture (multiple introductions) from different source populations (Novak & Mack, 1993;Genton et al., 2005). Genetic bottlenecks, however, do not seem to constrain invasive success (Sax et al., 2007), or even prevent rapid adaptive change (Prentis et al., 2008), as illustrated with the invasion case of Drosophila subobscura in Chile (Huey et al., 2005). Prentis et al. (2008) pointed out that even though genetic bottlenecks could enable rapid adaptive change to occur (through the conversion of epistatic variance to additive variance for example [Whitlock et al., 1995] or a complex interaction between inbreeding depression and a benign introduced environment [Schrieber & Lachmuth, 2016]) under special conditions, the genetic depletion of introduced population would generally impede fast adaptive change to occur.

In the same fashion as in ecological studies, evolutionary investigations of invasive species reported genetic features that could assist invasion success [START_REF] Lee | Evolutionary genetics of invasive species[END_REF]. For instance, inter-and intraspecific hybridisations could counteract genetic depletion of founder events and even create transgressive phenotypes [START_REF] Rieseberg | Major ecological transitions in wild sunflowers facilitated by hybridization[END_REF], or genomic rearrangements, like chromosomic inversions, could occur (Prevosti et al., 1988). A major question requiring deeper investigations concerns the substrate of genetic variation upon which natural selection could act for mounting adaptive genotypes/phenotypes in introduced populations with low additive genetic diversity. So far, hypotheses favour standing genetic variation over new mutations, because of the lower probability of the latest to happen, to be beneficial and to reach fixation [START_REF] Bock | What we still don t know about invasion genetics[END_REF].

An alternative (but not mutually exclusive) hypothesis to explain local adaptation of introduced species encompassing major loss of genetic diversity would be the phenotypic plasticity, with general purpose genotypes ( Dispersal of range expanding specimens more distant from the core population, should have direct fitness advantages. Indeed, recently established specimens should benefit from decreased intra-specific competition pressure (Travis & Dytham, 2002;[START_REF] Burton | Trade-offs and the evolution of life-histories during range expansion[END_REF]. Moreover, these founder individuals at the invasion front, supposedly characterized by a majority of individuals with good dispersal abilities, will share and transmit their genetic background (assortative mating). As this phenomenon repeats as the invasion front moves forward, dispersal traits should be enhanced at the leading edge of the range expansion, generating phenotypic differentiation between front and core individuals. Behind the front wave and in core populations, higher population densities should favour competitive abilities of individuals, rather than biological traits enhancing their dispersal capacities. The promotion of dispersal traits at the invasion front has been highlighted in the cane toad rapidly invading the north-east coast of Australia (Phillips et al., 2006[START_REF] Burton | Trade-offs and the evolution of life-histories during range expansion[END_REF], and this has led to the theory of spatial sorting (Shine et al., 2011).

Consequences of range expansion for population dynamics and potential of invasive species to encompass rapid range expansion and adaptation are now being extensively studied in theoretical and empirical works (Simmons & Thomas, 2004;Hughes et al., 2007;[START_REF] Léotard | Range expansion drives dispersal evolution in an equatorial three-species symbiosis[END_REF]Monty & Mahy, 2010;Sultan et al., 2013;White et al., 2013). Yet, our current understanding of the processes generating pheno-or genotypic variation in dispersal ability along the invasion gradient remains incomplete, especially under non-equilibrium conditions like range expansion and invasion.

Moreover, human-assisted dispersal events and multiple reintroductions impede our understanding of the actual expansion sequence. While theories suggest that spatial sorting may contribute selecting dispersive phenotypes at the front, the magnitude of this process is expected to be impeded by a range of life history trade-offs that may either facilitate or constrain the species' invasion success, with subsequent fitness consequences (i.e. constrained energetic outputs). This area of biological invasion seems very promising, and also challenging; for example, genome scans techniques traditionally allow to discriminate evolutionary forces occurring on the genome (demographic events or genetic drift impact the whole genome, selection acts on particular loci). But in the context of range expansion, drift is expected to be strong in the low density front populations, allowing random alleles (potentially deleterious) to arise from standing variation and reach high frequencies, thus to displaying a positive selection-like signal (Klopfstein et al., 2006). White et al. (2013) showed this problem could be solved by sampling replicated invasion front populations, as surfing produced by drift would result of independent allele selection , when adaptive trait promotion would impact the same loci.

The phenotypic differences generated by spatial sorting could help understand the genetic mechanisms underlying dispersal evolution [START_REF] Lombaert | Inferring the origin of populations introduced from a genetically structured native range by approximate Bayesian computation: case study of the invasive ladybird Harmonia axyridis[END_REF], as well as eco-evolutionary tradeoffs between functional traits such as dispersal, reproduction, growth. Understanding the dynamics and mechanistic of range expanding invasive populations would also be useful in other context, such as populations range shifts in response to climate change or introduction of biological control (White et al., 2013).

Presentation of the studied system: a ground beetle invading the French subantarctic Kerguelen Island

The subantarctic region, geographic context main representatives of Southern hemisphere s terrestrial ecosystems at mid Fig. 3 Differences and similarities of subantarctic islands ca.

much reduced as compared with the last glacial maximum (26.5 and 19 ka;[START_REF] Clark | The Last Glacial Maximum[END_REF], and only South Georgia and Heard Islands remain heavily glaciated, with ice-sheets covering respectively 57% and 80% of their total areas (see Tab. 1 for an overview of the main particularities of these subantarctic archipelagos, based on Chown et al., 1998;Chown & Convey, 2016). The different studies described in the following chapters have been designed in order to try to answer those questions.

An initial, but primordial investigation is presented in the Chapter 1. This work aimed at providing new insights into the biogeography of this species, by comparing population genetics of specimens of M. soledadinus from the Kerguelen Islands with other known representatives of this insect species, and to further compare the obtained genetic information with the historical data available for this insect. At a different scale, population genetics of specimens from the Kerguelen Islands sampled from populations along the invasion gradient are also unravelled as a first step allowing a better understanding of population dynamics and adaptive potential.

The second chapter focuses on the characterisation of the phenotypes of individuals sampled from different populations along the invasion gradient. We were interested in examining if the gradient of increased morphology accompanying expansion range was associated to changes in other life history traits, to investigate hypothesis on expansion-associated phenotypic modifications.

Habitat requirements of adults M. soledadinus are investigated in chapter 3, through experimental exposition of individuals to desiccating conditions. These abiotic conditions could have an effect on individual dispersal and constitute a significant ecological barrier to its geographic expansion.

The fourth chapter highlights new features on the autecology of M. soledadinus, through investigations of seasonal variations in major life history traits, in order to better understand ecological requirements and population dynamics.

Finally, the fifth chapter presents the phenotypic characteristics of individuals sampled along altitudinal gradients. In the context of climate change, we suggest that colonisation of altitudinal habitats should be facilitated, as climatic changes may alter abiotic and biotic environmental conditions, so that altitudinal habitats are progressively becoming suitable for M. soledadinus.

Parts of these studies were conducted in the field at the Kerguelen Islands (two stays of 3 months each during this three-year Ph.D), and under controlled conditions at the research station of

ALIENS and by SYNTHESYS.

Chapter 1

-Introduction

Despite the prominent ecological and socio-economic impacts of non-native species (Pimentel et al., 2005;Vilà et al., 2010), our knowledge of the main determinants associated with invasion success is still incomplete [START_REF] Richardson | Fifty years of invasion ecologythe legacy of Charles Elton[END_REF]Gurevitch et al., 2011). Not all non-native species become invasive following their introduction into new geographical areas (terminology defined in Falk-Petersen et al. [2006]), likely because of the diversity of interconnected biotic and abiotic parameters that drive invasion success (Williamson, 2006). In parallel, several theories, including the evolution of increased competitive ability, the novel weapon hypothesis or the enemy release hypothesis have been formulated over the past decades to try explaining how non-native species successfully overcome novel environmental filters (Callaway & Ridenour, 2004;Colautti et al., 2004;Handley et al., 2008;van Kleunen et al., 2010). Invasiveness has also been suggested as a pivotal determinant of invasion rate (Williamson & Fitter, 1996;Kolar & Lodge, 2001), and the plasticity of traits, such as fecundity, longevity, together with dispersal capability and stress resistance are of tremendous importance for the successful establishment and subsequent expansion of non-native organisms. However, there are often large shortcomings in our understanding of the biology and autecology of non-native species in introduced areas, thus impairing the understanding of invasion process.

At the sub-Antarctic Kerguelen Islands, located in the south Indian Ocean (48°30 -50°S, 68°27 -70°35 E) and subject to cold oceanic climate, multiple insect species have been accidentally introduced to the point that the archipelago now hosts more non-native than native species of arthropods (Frenot et al., 2005;Lebouvier et al., 2011). Among the introduced insects, several have spread significantly despite extremely limited human assistance, if any (Frenot et al., 2005;Lebouvier et al., 2011). The predatory carabid beetle Merizodus soledadinus (Coleoptera: Trechidae) was accidentally introduced from the Falkland Islands in 1913 in a single site of the Kerguelen Islands (Port Couvreux; 49°17 04.9 S, 69°41 41 E, Fig. 1), where the species was first observed in 1939 (Jeannel, 1940). Historic data and longterm monitoring of the expansion of this flightless insect has showed that it colonised localities nearby the introduction site first, then spread along the north coast of the main island, and ultimately invaded several islands of the Golfe du Morbihan (likely human-or bird-assisted introductions, or passive dispersal by flotation; see Renault [2011]). When established, this predator becomes the dominant species in the colonised habitats and generates significant ecological impacts on native fauna, particularly endemic Dipterans (Ottesen, 1990;Ernsting, 1993;Todd, 1996Todd, , 1997;;Chevrier et al., 1997;Lalouette et al., 2012). Renault, 2016) and salinity (Hidalgo et al., 2013). Conversely, adults did not survive longer than two days when relative humidity decreased below 70% of relative humidity (Ouisse et al., 2016), which is consistent with the main habitats where this species thrives [START_REF] Chevrier | Characterization of the habitats colonized by the alien ground beetle Merizodus soledadinus at the Kerguelen islands[END_REF]. Meanwhile, data are still missing regarding several important key elements relative to its biology (e.g. longevity, fecundity or prey preferences). The few studies conducted on this species reported by Chevrier et al. (1997) mentioned a continuous presence of adults throughout the year in the Kerguelen Islands but no published empirical data are available for these observations. In South Georgia, another sub-Antarctic island invaded by this insect (Ernsting, 1993;[START_REF] Brandjes | Spatial dynamics of two introduced species of carabid beetles on the sub-Antarctic island of South Georgia[END_REF], females egg load ranged from three to six eggs in females, and the absence of corpora lutea in females at the onset of summer periods (Ernsting, 1993) suggested a single breeding period.

The aim of this work is to improve our knowledge of the ecology of M. soledadinus at the Kerguelen Islands. To estimate adult longevity, a survival experiment was designed under controlled conditions. Based on female s reproductive status in South Georgia (Ernsting, 1993), we hypothesised an adult life span of 1-2 years. The number of eggs carried by females over the year was also investigated, since high reproductive investment can be a key characteristic in the rapid success and i.e.

-

Material & Methods

Estimation

-Discussion

Our study found a median adult longevity of about eight months. Adults were regularly fed and supplied with water over the duration of the experiment, and benefited from favourable thermal conditions. These experimental conditions may have elevated longevity as compared with the likely life span under natural conditions. On the other hand, at the Kerguelen Islands, M. soledadinus can feed on abundant prey in most localities and only suffers from occasional mice predation in some invaded microhabitats [START_REF] Roux | Diet of the house mouse (Mus musculus) on Guillou Island, Kerguelen archipelago, Subantarctic[END_REF] and cannibalism. Moreover, adults are also able to endure natural thermal conditions cooler than those applied in the present experimental setting (Lalouette et al., 2012;[START_REF] Lombard | Comparative salinity tolerance in native flies from the subantarctic Kerguelen Islands: a metabolomic approach[END_REF], which may even slow down ageing processes and augment longevity.

Rearing trials of M. soledadinus were not successful, preventing us to estimate the exact life span and total life cycle of this species. In the present work, the sampling period maximised the number of teneral individuals caught to allow more realistic estimations, and the calculated adult life span is more likely underestimated than overestimated. No peak of mortality was observed during the very first months of the experiment, and mortality largely increased one year after insect collection (between days 310 and 340, ca. 33% of beetles died). Our measurement is consistent with life span estimations earlier reported by Ernsting (1993) based on egg load and assumptions on the life cycle of M. soledadinus in South Georgia. Data reporting carabid longevity are scarce, and range from one to seven years depending on the species, with estimations based on mandibular or claw wear, reproductive status and number of overwintering periods (Thiele, 1977;[START_REF] Lövei | Adult mortality and minimum lifespan of the ground beetle Harpalus affinis (Coleoptera: Carabidae) in New Zealand[END_REF].

The adult life span of M. soledadinus is similar to native carabid beetles, including Amblystogenium pacificum and A. minimum which belong to the same feeding guild in other sub-Antarctic islands (Davies, 1987). The invasive M. soledadinus seems, however, to display a lower seasonality in its life cycle as well as an increased investment in reproduction (number of eggs in the ovaries) compared with this carabid beetle native from Crozet archipelago.

Our field observations at the Kerguelen Islands (Laparie, Lebouvier, Renault, unpublished data) correspond to Ernsting s (1993) reports from South Georgia, and likely suggest an emergence period ranging from September to April, with the main peak of tenerals around February-March.

Gravid females were found across the whole year, and the number of eggs in the ovaries did not vary significantly over time. This finding suggests that egg-laying can theoretically occur at any time and result in high phenological variance, although higher summer activity may exacerbate reproduction.

This result is in contrast with the semelparity of the ground beetle hypothesised by Ernsting (1993),

i.e. one reproductive season per individual. Females of long-lived carabid species are usually capable of multiple cycles of egg maturation. For instance, Abax parallelus [START_REF] Löser | Brutfürsorge und Brutpflege bei Laufkäfern der Gattung Abax[END_REF], Pterostichus chalcites Kirk, 1975)or A. pacificum (Davies, 1987) exhibit several consecutive egg-laying periods. Associated with a low periodicity of the life cycle, multiple egg-layings may conceal any inter-individual variance

(
Chapter 1 in seasonality of the egg load. In our work, the number of eggs per female was higher than reported in South Georgia by Ernsting (1993), even though we examined fewer individuals. Climatic conditions are harsher in South Georgia than at the Kerguelen Islands (Chown et al., 1998), and may thus be more restrictive and impair investment in reproduction.

The year round trapping of adult M. soledadinus is consistent with previous studies on this species (Kerguelen Islands: Chevrier et al., 1997;South Georgia: Ernsting, 1993), and demonstrated continuous activity of adults. From our 10-year investigation, the peak of trapping occurred during summer, and is likely associated with a peak in the reproductive season of this insect (as demonstrated through similar methodology in Pterostichus madinus in Luff [1973]). Importantly, Jeannel (1940) sampled all life stages of M. soledadinus at once in summer at the Kerguelen Islands, also suggesting the long-lasting developmental period of this species and the aforementioned phenological variance within populations. Lower pitfall catch rates during winter periods together with an average adult life span over one year suggest seasonal changes in adults locomotor activity related to thermal conditions rather than a demographic decrease. This assumption is consistent with the results of Ottesen (1990) who found a positive correlation between daily activity of this insect and ground temperature.

The decreased activity of M. soledadinus during the Austral winter, whether it is caused by, or consequential to, the colder environmental conditions, may contribute sparing body reserves in a period where several native and introduced prey species are inactive or scarcer. Interestingly, amounts of glycogen and protein did not exhibit large variations over the year, whereas starving M. soledadinus were earlier characterised by declining amounts of sugars and lipids [START_REF] Colinet | Exploring the plastic response to cold acclimation through metabolomics: metabolomics of cold acclimation response[END_REF]. Our present data suggest that adults continuously feed during the supposedly less favourable winter season.

Merizodus soledadinus have been described as opportunistic predators fond of Diptera maggots (Chevrier et al., 1997), implying the possibility of diet adjustments towards other available prey in winter periods. For instance, they have been shown to feed on the native beetle Hydromedion sparsutum on South Georgia [START_REF] Convey | Recent range expansions in nonnative predatory beetles on sub-Antarctic South Georgia[END_REF]. This idea is supported by variations of triglycerides whose amounts did not vary much over the seasons. The only remarkable variation was observed at the onset of the summer period, with amounts of these stored lipids being augmented and more variable, likely revealing the return to maximal activity in parallel with increased food availability.

Meanwhile, our samples were composed of whole body extracts and were not controlled for sex ratio.

It is thus hard to determine the relative lipid part reflecting egg maturation, and the relative contribution of each gender to these lipid variations. Finally, resorption of unlaid eggs in females (Rosenheim et al., 2000), or cannibalism on laid eggs by males and females, cannot be excluded during extended periods of food deprivation. This chapter presents the advancement status of the investigations on population genetics of M.

soledadinus.

Highlights

-Comparison of genetic diversity patterns between specimens of M. soledadinus from (i)

Patagonia, South Georgia and Kerguelen and (ii) ten populations distributed along the invasion gradient at the Kerguelen Islands.

-Individuals from the Kerguelen Islands are less genetically diverse than in South Georgia and in Patagonia; investigated populations along the invasion gradient are not genetically structured.

-Supplementary locations need to be added to (i) complete the biogeography of this species and

(ii) further test for human-assisted introductions Introduction

Investigations on population genetics recently became a recurrent feature in invasive species studies.

These studies allow to infer the geographic origin of the sampled specimens, and routes of introduction of alien species (Estoup & Guillemaud, 2010). In fine, these data allow us gaining a posteriori precious information on the history of invasion cases (Dlugosch & Parker, 2008;Hufbauer & Sforza, 2008;[START_REF] Lombaert | Inferring the origin of populations introduced from a genetically structured native range by approximate Bayesian computation: case study of the invasive ladybird Harmonia axyridis[END_REF]Cristescu, 2015). Genetic studies are also cornerstones for understanding the level of selection alien species endured, and their subsequent evolutionary ecology.

Altogether, it allows a better understanding of the invasion and adaptation processes, and on the effects of evolutionary forces on species genomes [START_REF] Lee | Evolutionary genetics of invasive species[END_REF]Sax et al., 2007).

Invasive Extracted DNA was digested by the restriction enzyme SbfI (which targets restriction sites 5

CCTGCAGG 3 ). Individuals barcodes were then ligated to each side of the restriction fragments, which were then randomly sheared (sonication). Through electrophoresis, fragments 300 < length < 700bp were selected and purified. On the 3 and 5 ends of each DNA strand, an adenine was ligated, on which secondary barcodes (specific of the library and containing flowcell annealing sites) ligated.

Finally, 14 to 16 cycles of a test PCR allows to verify the quality of each library created.

The first RAD library was 300bp paired-end sequenced on an Ilumina MiSeq platform (The Gene Pool, Ashworth lab, University of Edinburgh) and the seven other libraries were 100bp pairedend sequenced on an Illumina HiSeq1500 platform ( Biogeography libraries (N=2) were sequenced

The Gene Pool, Ashworth lab, University of Edinburgh; Kerguelen populations genetic libraries (N=5) were sequenced at the Medical Genomics Institute, UZ Antwerp Hospital, Belgium).

c) Sequenced data processing

To process the RADtags, we first assembled the 2x300bp MiSeq reads of a single individual with the highest coverage (Bel01) to generate a set of reference tags. Reads were assembled using

Velvet (Zerbino & Birney, 2008).

Used that way, this software allows to reconstruct the approximate 700bp fragments sequenced on each side of restriction sites, creating two contigs per restriction site. Velvet parametrization required to define the Kmer length (the length of each subunit of a contig, to assemble together), the insert length (the length of the sequenced fragments). We defined the following parameters: Kmer length = 31bp, insert length = 450bp, coverage cutoff = 10 reads per position minimum. We verified the quality of the assembly by plotting the coverage and length of the obtained contigs and retained only those with a read length > 450bp and a coverage between 10 and 110. After filtering we retained 2040 high-quality contigs.

Next, we mapped the reads of each individual against the reference RADtags with BWA (Burrows-Wheeler Aligner software, [START_REF] Li | Fast and accurate long-read alignment with Burrows-Wheeler transform[END_REF]. SNPs were subsequently called with GATK (Genome Analysis ToolKit software, McKenna et al., 2010;DePristo et al., 2011;Van der Auwera et al., 2013), which resulted in a VCF file that was used for appropriate filtering to retain a set of high-quality SNPs. One individual from South Georgia (SGF5) was removed from the dataset, as very few reads mapped against the reference tags. This suggests that the sequenced specimens belongs to a different species (Trechisibus antarcticus) that is morphologically closely related to M. soledadinus.

From this step, data analyses were separated, with one part focusing on the biogeography dataset on one hand (individuals sequenced in the second and third libraries), for which wo obtained 1077 SNPs shared by 90% of the individuals, and on the other hand the individuals sampled in the ten distinct localities of the Kerguelen Islands, for which we obtained 4271 SNPs shared by all sequenced individuals.

Chapter 2

Summary statistics were computed using Geneop 4.4 (Raymond & Rousset, 1995;Rousset, 2008), including Hardy-Weinberg exact tests, inbreeding coefficients (FIS) and differentiation between populations (pairwise FST). The genetic structure of populations was investigated independently for the two main datasets (Biogeographical scales and Kerguelen scale) using Structure 2.3.4 (running settings: admixture ancestry model and correlated allele frequencies; Pritchard et al., 2000) and

StructureHarvester (Earl, 2012) was used to determine K, the number of clusters. Heterozygosity data were extracted from the VCF file using VCFTools. The sampling location (for the Biogeographical analysis) and the effect of residence time of populations (for the Kerguelen population s genetic analysis) on heterozygosity values were statistically tested with linear regressions (R. 3.3.0, R Core

Team, 2016). Isolation by distance was investigated on the populations from Kerguelen Islands by testing the correlation between the genetic distance (FST) matrix and the matrix of Euclidian geographic distances (mantel tests, 999 permutations, package vegan), using R 3.3.0.

-Results

a) Biogeography

A total of 561 SNPs were shared by at least 90% of the individuals sampled in the three studied biogeographic regions (Kerguelen Islands, South Georgia, Patagonia). These three biogeographic between South Georgia and Kerguelen Islands (FST =0.0016).

The inbreeding coefficient FIS is negative for all individuals from the three geographic regions (Kerguelen Islands =-0.029, Patagonia = -0.106, South Georgia = -0.133). These results show increased heterozygosity compared with random mating for the three populations, especially South Georgia.

Heterozygosity values revealed significant differences among insects of the three localities (χ²=7.35, P <0.01). Post-hoc tests outline that individuals from Kerguelen Islands host lower levels of heterozygosity than individuals from Patagonia (t =-3.78, P<0.01), the two other comparisons being non-significant (South Georgia-Patagonia: t =-2.23, P =0.08; Kerguelen Islands-South Georgia: t =-1.54, P =0.28). However, we found that heterozygosity of individuals is correlated with the mean sequencing depth (see Fig. 3), probably skewing the results.

-Discussion

a) Biogeography

The comparison of genetic diversity and population structure among three geographic regions, out of the four occupied by M. soledadinus, revealed that the Kerguelen Islands host a population less diverse than in Patagonia and South Georgia. Specimens from South Georgia show a higher level of genetic diversity compared with their counterparts from the Kerguelen Islands. This is interesting, as M. soledadinus was first observed 53 years ago in South Georgia, whereas it has been observed 103 years ago at the Kerguelen Islands. The higher genetic diversity of insects from South Georgia could be explained by multiple introduction events to this island, located closer to the Falkland Islands, and thus more likely to have experienced more transportations and introductions of M.

soledadinus. It is also important to mention that Falkland Islands represent an important route of transit in order to get access to the subantarctic South Georgia. If multiple introduction events have occurred at South Georgia, this would have increase the chances of admixture among insects of distinct genetic lineages, thus explaining the increased levels of diversity observed in this island. This hypothesis will have to be confirmed by incorporating into our analyses specimens of M. soledadinus from the Falkland Islands.

Coverage values highlighted that sequences of South Georgian and Patagonian individuals were generally of lower quality than the sequences from specimens from the Kerguelen Islands, and would probably require resequencing. This lowered quality could partly explain the lower amount of polymorphic loci detected in these individuals compared with the analysis of population genetics along the invasion gradient at the Kerguelen archipelago. This pattern could also be due to the use of an individual from Kerguelen as reference genome ; this procedure could have increase the degree of divergence among populations, further lowering the proportion of RAD-tags matching.

b) Population genetics of the invasive carabid beetle M. soledadinus at the Kerguelen Islands

As hypothesized, adult M. soledadinus from Port Couvreux are characterized by the highest level of genetic diversity, as compared with the other sequenced specimens, from ten localities of the Kerguelen Islands. Again, this finding supports the hypothesis of a single introduction event in the locality of Port Couvreux, further followed by natural stepping-stone dispersal events. There is no detectable population structure among specimens from the ten sampled populations, which could be explained by a combined effect of reduced genetic diversity and recent history of this introduction. In parallel, the absence of genetic structure at the scale of the Kerguelen Islands could also depict a high

Chapter 2

frequency of migration events among populations, a process that could be reinforced in some localities by human transportations. These two processes would greatly contribute to homogenising the pool of genetic diversity.

Conflicting this absence of genetic structure, heterozygosity values display a strong pattern of reduced genetic diversity along the invasion gradient. This result supports the hypothesis of range expansion from the initial and unique introduction locality of Port Couvreux, with progressive colonisation of uncharted sites by few dispersers. However, no patterns of isolation by distance were detected. Euclidian geographic distances may have constituted imperfect metrics for this species whose range expansion patterns primarily follow coastal habitats. In future investigations, leastresistance path analyses, attributing higher resistance values to altitudinal habitats for example, could be more appropriate to understand the colonisation process of M. soledadinus at the Kerguelen Islands (Wang et al., 2009;Spear et al., 2010). Finally, spatial sorting resulting from the ongoing range expansion of this species may mask population differentiation if it is based on neutral genetic markers only. Indeed, spatial sorting acts as a selection mechanism, and few genes might be involved in phenotypic sorting (Shine et al., 2011). A first exploratory step into this direction would be to search within the dataset for outlier loci, as realised in (Vandepitte et al., 2014).

We suggest that adding genetic sequences of individuals from the research station of Portaux-Français would be valuable and informative. Knowing the genetic diversity of specimens from this locality would allow to estimate the genetic composition of M. soledadinus, these individuals being an important dissemination source for the colonisation of several localities of the Kerguelen Islands, more particularly for islands of the Golfe du Morbihan. Such implementation is indispensable for assessments of human-mediated introductions from the research stations.

The specimens from Estacade have a very low genetic diversity (but from the FIS values, this is the least inbred population of the ten sequenced populations, which is a conflicting result). This population was first observed between 1995 and 2000, and most probably results from the transportation of some few individuals (maybe a single gravid female) by humans to this locality.

Indeed, this locality hosts a hut where research activity took place, and is, in addition, on the main path that as used bytractors for resupplying 4-8 times per year the site of Ratmanoff (the largest studied colony of king penguin at the Kerguelen Islands). The activities at the locality of Estacades et al., 2011;Chown et al., 2015). The number of exotic species invading terrestrial and aquatic habitats has increased strongly, and even if some exotic organisms may have beneficial effects on invaded communities and ecosystems (Simberloff & von Holle, 1999;MacDougall & Turkington, 2005), most of them have been reported to cause serious threats to native biota (see Vilà et al., 2011). Beyond the pure ecological causes and consequences of biological invasions, this phenomenon often represents valuable situations for real-time monitoring of phenotypic and genotypic changes associated to establishment and range expansion of invasive organisms (Sax et al., 2007;Davis, 2009). In this context, species adaptations and spatial sorting of invasive populations along colonisation gradients are fascinating, yet also intriguing, and these processes have become a hot topic in invasion studies (Phillips et al., 2006;Monty & Mahy, 2010;White et al., 2013;Tingley et al., 2014).

Dispersal performance represents a prominent aspect that triggers the distribution of rangeshifting species, and likely coevolves with functional traits driving fecundity and/or growth rates (Hanski et al., 2006). General concepts of population ecology suggest that leptokurtic dispersal distributions represent a common pattern (Kot et al., 1996), with large amounts of individuals residing in a given locality (e.g. the residents ), and decreasing amounts of specimens that effectively disperse (e.g. the dispersers ). However, our current understanding of the evolutionary processes generating such pheno-or genotypic variation in dispersal ability remains incomplete, especially under nonequilibrium conditions like range expansion and invasion (Kinlan & Gaines, 2003;Fitzpatrick et al., 2012). Pioneer studies were conducted on the cane toad, and reported that dispersal performance was increased with an exponential fashion in Australia. Specifically, cane toads sampled at the invasion front are characterised by higher body sizes, locomotor performance, and more straight dispersal paths than their non-dispersing counterparts (Phillips et al., 2006;Alford et al., 2009;[START_REF] Brown | The straight and narrow path: the evolution of straightline dispersal at a cane toad invasion front[END_REF]. The correlation between dispersal ability and body size extends to serval insect species (Juliano, 1983;Gutiérrez & Menéndez, 1997;Zera & Denno, 1997). In addition, in some insect taxa, the expression and allelic diversity of the gene encoding phosphoglucoisomerase (PGI) has been proven a powerful estimator of dispersal capacity of individuals (Mitikka & Hanski, 2010;Niitepõld, 2010).

In most factual cases of invasion phenomena, human-assisted dispersal events can impede our understanding of alien species range expansion (Walther et al., 2009), which has thus often been hung over through modelling (Travis & Dytham, 2002;[START_REF] Burton | Trade-offs and the evolution of life-histories during range expansion[END_REF]Perkins et al., 2012). While theories suggest that spatial sorting may contribute by selecting dispersive phenotypes at the front distribution margins, the magnitude of this process is expected to be impeded by a range of life history trade-offs that may either facilitate or constrain the species' invasion success, with subsequent fitness consequences (i.e. constrained energetic outputs; [START_REF] Burton | Trade-offs and the evolution of life-histories during range expansion[END_REF]. Subantarctic islands are ideal laboratory-system to address this kind of questions. Briefly, these islands are remote from continental

Chapter 3 ecosystems and main commercial routes. Human presence is recent, and when there are research stations, buildings are restricted to a narrow part of these islands.

Despite reduced anthropogenic activity and presence at the subantarctic islands, a number of invasive plants, mammals and insects has been introduced (Frenot et al., 2005), and their subsequent natural range expansion monitored [START_REF] Convey | Recent range expansions in nonnative predatory beetles on sub-Antarctic South Georgia[END_REF]Lebouvier et al., 2011). At the Kerguelen Islands for instance, the carabid beetle Merizodus soledadinus was introduced in 1913 at a single locality, yielding a century of dispersal, without human assistance in a significant number of colonised localities. In this insect species, Laparie et al. ( 2013) investigated morphological differences between individuals whose populations differed in time since establishment (hereafter referred to as residence time). These authors found that adult M. soledadinus sampled from recently established populations were bigger than individuals sampled from formerly established populations. Even if several hypotheses can be mounted for explaining these body size differences, this consistent pattern among different animal taxa of distinct trophic regimes requires further attention.

Spatial sorting is the prominent explanation for explaining changes in body sizes during range expansion. Individuals of bigger sizes often have better abilities to disperse (higher dispersal performance and success) over larger geographic ranges. When established, the assortative mating of these individuals further contribute to maintain higher body sizes, as demonstrated experimentally in the damselfly Coenagrion scitulum (Therry et al., 2015). Generation after generation, front populations thus carry biological traits associated with enhanced dispersal performance and capabilities. For instance, empiric studies reported longer legs, bigger thoracic muscles, increased muscular efficiency, stronger tolerance to starvation or to other abiotic stressors, and higher body stores (Hill et al., 1999;Haag et al., 2005;Phillips et al., 2006;Hughes et al., 2007;Kelehear et al., 2012;[START_REF] Lombaert | Rapid increase in dispersal during range expansion in the invasive ladybird Harmonia axyridis[END_REF].

Conversely, in formerly established populations, the higher population density and the qualitative and quantitative decline of food resources increase intra specific competition. This can supposedly lean towards the production of higher amount of eggs by females (to counteract completion-induced mortality of the juveniles) and faster developmental rates of the juveniles, both processes acting jointly and resulting in adults of smaller body sizes (Amundsen et al., 2012).

In a recent work, Van Petegem et al. ( 2016) ran metabolomics approaches to explore the metabolic phenotypes of the two-spotted spider mite along an invasion gradient. While mites were reared in common garden, these authors reported evident signs of metabolic adjustments, with specimens from the invasion front tending to exhibit metabolic activity oriented towards more intense energetic production. Meanwhile, populations were not replicated, which, together with the unknown residence time of the sampled specimens, hampers the drawing of general conclusions.

In the present study, we aimed at conducting a large-scale phenotyping of specimens of M.

soledadinus sampled from populations with different estimated residence times. As a prerequisite, we

Chapter 3 first wanted to confirm the results obtained by Laparie et al. ( 2013), using different populations. In a second step, we explored the potential effects of residence time on several different phenotypic traits related to, or that should promote dispersal performance, i.e. locomotor performance, propensity to disperse, starvation resistance, enzymatic assays, and GC-MS-TOF metabolic phenotyping. To our knowledge, this is the first study that integrates all of these elements together. We believe that this is a useful way to detect variations among functional traits in invasive populations of alien insects, and delineate the complex eco-evolutionary trade-offs responsible for sex-specific dispersal-related phenotypes. We hypothesise that morphological proxies and dispersal performance correlates (locomotor activity, dispersal propensity) will be higher in specimens of M. soledadinus from the invasion front. Then, as dispersal performance is supposedly increased along the invasion gradient, we should see changes in some of the following aspects: increased amounts of metabolic stores, modulation of enzymatic flux capacities, dispersal-associated shift in the trophic pathways to promote reserve accumulation and dispersal decisions.

-Material and Methods

a) Sampling locations

Adult M. soledadinus were hand-sampled under rocks on the main island of the Kerguelen archipelago (see Fig. 1). Insects were collected from a total of ten localities along the invasion gradient, with a residence time ranging from 103 to 4 years. Insect sampling occurred during the austral summers 2014-2015 and 2015-2016. Due to the constrained field logistics in subpolar regions, slight changes in the visited localities occurred between these two working periods, meaning that not all populations were systematically tested for all the large-scale phenotyping. Meanwhile, this does not affect our experimental design, which focused on the residence time of the specimens rather than the localities per se. Cataractes were numbered at the end of the experiment. In one replicate of Isthme Bas, only four individuals were found at the end of the experiment, and this replicate was discarded.

f) Enzymatic assays

A total of six enzymatic assays were performed on fresh individuals brought back from the Kerguelen Islands to the Metropolitan France: total antioxidant activity, hexokinase (HK) and phosphoglucose For the total antioxidant activity, ten microliters of the supernatant were used for the assay, and activity was quantified from the drawn trolox standard curve (absorbance red at 750nm).

For the PGI assay, three µL of the supernatant were diluted into 47µL of assay buffer, before being used for the quantification of PGI activity. A NADH standard curve was done to estimate the rate of conversion of fructose-6-phosphate to glucose-6-phosphate, with the absorbance red at 450nm, during a 9min reaction (except for two replicates of Isthme Bas, two replicates of Cataractes and one replicate from Val Studer, for which the reaction rate was calculated over a 6 min interval).

For the HK assay kit, 6µL of extraction supernatant, diluted in 44µL of assay buffer were used to quantify Hexokinase activity, using a NADH standard curve to estimate the rate of Glucose to Glucose-6-Phosphate conversion, with the absorbance red at 450nm, during a 9min reaction (except for a 6min reaction for a replicate from Cataractes).

 Mitochondrial extractions and quantification of citrate synthase, fumarase and malate dehydrogenase activities Mitochondrial extractions were performed following the instructions of the Cayman MitoCkeck Mitochondrial isolation kit n°701010. Samples constituted by two alive beetles were grinded into 1.5mL of ice-cold homogenization buffer using a bounce homogenizer. Subsequent homogenate was filtered through a 300µm mesh and transferred into a polycarbonate centrifuge tube before being centrifuge for 10min at 10 000g at 4 °C. Supernatant was then discarded and the pellet was re-dissolved in 300µL of isolation buffer. Mitochondrial enzymatic assays were performed following the instructions of the Sigma assay kits MAK193 (Citrate Synthase), MAK206 (Fumarase) and MAK196 (Malate Chapter 3

DeHydrogenase -MDH). We used 50µL of mitochondrial extract to quantify citrate synthase and fumarase activities, but for the MDH, 15µL of mitochondrial extract were diluted in 35µL of isolation buffer before the assays. The citrate synthase activity was quantified at 412nm (25 °C), whereas MDH and fumarase activities were quantified at 450nm (37 °C). For the three assays, the absorbance was red every minute for 10 minutes. Only the linear part on the kinetics (at least three consecutive values of the obtained curve) for each sample was selected to calculate the rate of the reaction. Then, 1mL of extraction solvent (isopropanol:acetonitrile:water, volume ratio 3:3:2) was added before centrifugation (12 800g, 2min, 4 °C). The supernatant was separated into two equal aliquots and vacuum-dried for 4h (Centrivap cold trap, LabCono, Kansas City, MO). Two microliters of a mixture of internal retention index markers, and 10µL of a 20mg.mL -1 solution of methoxyamine hydrochloride in pyridine were added to the dried extracts which were further vortexed. Then, a volume of 90µL of N-methyl-N-trimethylsilyltrifluoroacetamide with 1% trimethylchlorosilane was added, and the samples were incubated for 30min at 37 °C. A Gerstel CIS cold injection system (Gerstel GmbH, Müllheim, Germany) provided the injection of 0.5µL of each sample at a rate of 1mL.min -1 at an initial temperature of 50 °C, ramping to 250 °C at 12 °C.s -1 . Gas chromatography was conducted with an Agilent 6890 equipment, with a 30m column (⌀ 0.25mm); mass spectrometry was conducted with a Leco Pegasus IV. Algorithmic processing of the raw data by ChromaTOF 2.32 software allows to attribute peaks to metabolites, for which quantification is reported as peak height.

Chapter 3

h) Statistical analyses

For the analyses, the residence time of the sampled populations was used as a continuous explanatory variable to test for phenotypic responses depending on the population status. Two scales of residence time were used: the experiments that used adult M. soledadinus sampled and experimented during the austral summer 2014-2015 were analysed along a colonisation scale ranging from 102 to 3 years (morphometry, starvation resistance, locomotor activity and metabolic phenotyping); the experiments performed on ground beetles sampled during the austral summer 2015-2016 were analysed along a 103 to 4 years old gradient (propensity to disperse, enzymatic assays).

Morphological changes along the invasion gradient

We used the analytical procedure described in Laparie et al. ( 2013 ). This matrix was then compared with the residence time matrix obtained between each population, using mantel tests (10 000 permutations) in order to quantify trait size modifications.

Starvation resistance

The comparison of starvation resistance among populations was first investigated by computing lethal times (LT50 and LT90) with survival regression models (survival package, Therneau, 2013). In these models, explanatory variables were sex, residence time and their interaction. Survival duration to starvation was also analysed with linear regression models by considering the number of days each individual survived, as a function of residence time and initial fresh mass. The dynamics of body mass loss until death by inanition was computed as the proportion of fresh mass lost between the first day of the experiment and the last fresh mass recorded for each monitored individual. These data were analysed through linear models, with residence time and sex as the explanatory variables.

Locomotor activity

The substantial dataset resulting from the monitoring of the locomotor activity of adult M. soledadinus was first reduced by extracting the number of passages per hour and per population. An increase activity peak was recorded for all individuals between 7h05am and 7h20am, probably caused by the sudden programmed lighting of the room; these periods of 15 minutes were removed from the dataset.

Of note, this pattern was not observed when the light was turned off in the evening. The effects of population s residence time and period of the day (simulating daytime and night time) on locomotor

The proportion of individuals that had left the home box (the individuals in the tube were considered

Enzymatic assays

Metabolic fingerprinting vegan metabolites matrix to delineate ′ ~ log

-

Results

Morphological changes along the invasion gradient

Enzymatic assays

Fig Larger individuals can reach more distant localities during colonisation events, as a result of complex interconnections and interactions among ecological, morphological and biological characteristics. Specifically (non-exhaustive list), longer legs, higher muscle mass, larger body reserves, lower competition in newly colonised habitats should enhance dispersal performance, and should increase the probability of dispersal events over higher geographic distances. This process repeats as the invasion wave progresses, thus reinforcing the phenotypic distinction between front (disperser) and core (resident) populations. Moreover, competitive ability and energetic allocation also play a central role in setting body size patterns along invasion gradients. Core populations are often close to their carrying capacity, meaning that intra-and inter-specific competition is often high. In these conditions, resource allocation to competitive ability must be increased, in addition to the laying of a higher amount of eggs of smaller sizes by females (bet hedging strategy should be promoted, together with higher egg production, as the hatching probability is assumed to decline in core Chapter 3 populations, at least for predatory species such as M. soledadinus). Performance of dispersal, reproduction and competitive ability has been suggested to significantly interconnect (Travis et al., 2009), and this is even truer for the last two biological traits. As intraspecific competition is highly reduced at the invasion front, a higher investment towards reproduction can be expected. This higher reproductive investment should be accompanied by the laying of a small amount of eggs of bigger sizes, as the hatching rate is supposedly higher at the invasion front.

The behavioural, physiological and biochemical changes associated with morphological differences along invasion gradients remain largely unexplored in entomological studies. Several authors suggested the existence of different phenotypes among core and range populations (Lyytinen et al., 2009;Laparie et al., 2013;[START_REF] Lombaert | Rapid increase in dispersal during range expansion in the invasive ladybird Harmonia axyridis[END_REF]Therry et al., 2015), but the association of traits, altogether forming a syndrome of dispersal in front populations remain non-elucidated. The largescale phenotyping study we conducted showed that, in controlled conditions, adults from range margin populations exhibit higher locomotor activity. Increased movement performance is an explicit advantage for colonising individuals. However, this advantage can be significant in successfully reaching more distant locations, only if individuals disperse using straight trajectories [START_REF] Conradt | Nonrandom movement behavior at habitat boundaries in two butterfly species: implications for dispersal[END_REF]Delattre et al., 2010). Displacement patterns could then be investigated to further explore dispersal behaviour of adult M. soledadinus.

As a complement of the locomotor activity, we studied another dispersal-related behavioural trait, by assessing the propensity of individuals to leave a patch. No difference was found between populations, which could mean that the same proportion of disperser/resident insects occur within the tested populations. This experimental design could be further use to sort out individuals according to their behaviour. Indeed, bolder adult M. soledadinus could have leave the pipe quicker, whereas shy individuals stayed longer into the patch. Because experiments were only conducted at one single density (10 individuals per patch), it is possible that individuals behave as trendy lemmings in this experiment, following explorers. We must thus acknowledge that this study, instead of comparing dispersal propensity, may have more likely tested for behavioural sorting (Cote et al., 2010).

Dispersal is a costly behaviour, in terms of risk undertaken and energetic investment (see [START_REF] Bonte | Costs of dispersal[END_REF] for a review). Front populations host larger individuals of M. soledadinus, and this has been assumed to increase the amount of body stores, in turn allowing these insects to withstand longer periods of starvation and/or better cope with abiotic stressors [START_REF] Hance | Is body size an influential parameter in determining the duration of survival at low temperatures in Alphitobius diaperinus Panzer (Coleoptera: Tenebrionidae)?[END_REF]. Indeed, even if dispersal is costly, the interruption of reproduction during this period can balance this cost, and thus, an individual having larger body reserves have greater chances to cover longer geographic distances and successfully reach another habitat patch. This assumption should be particularly relevant in landscapes where favourable patches are fragmented. Here, we compared starvation resistance of insects, as well as temporal dynamic of mass loss during food deprivation, among insects sampled from core populations and those sampled from edge populations. Survival durations of insects Chapter 3 from range edge populations was significantly increased compared with insects from core populations, and the ability to cope with starvation was generally enhanced in heavier individuals. According to our results, males gained along the invasion gradient comparatively more resistance to starvation than females. Increased body size in males from recently established populations, was primarily influenced by the size of their abdomen. The larger amount of body reserves that could be stored if abdomen size are larger could enhance resistance to starvation. Nevertheless, this could only be efficient if the global energetic needs of these larger insects are lower, or at worst equivalent, than those from small insects.

The increased performance to cope with food deprivation in adult M. soledadinus sampled in recently colonised localities should be assisted by adjustments of metabolic activities, with enzyme activity oriented towards a higher production of storage reserves. The total energy diverted to the different functional traits of organisms generates trade-offs [START_REF] Cody | Short-term evolution of reduced dispersal in island plant populations[END_REF]. Consistently, Harrison et al. (2006) highlighted the importance of physiological trade-offs in determining dispersal and range limits of invasive honeybees. We did not investigated the performance of would other energy-consuming life traits (somatic maintenance, competitive ability, immunity, mating…), and did not quantify and compared among populations the costs of reproduction and dispersal. We rather focused on biochemical correlates, by comparative assessments of activities of enzymes of glycolytic and tricarboxylic cycle pathways. The most significant difference was measured between males and females, which may probably result from the higher energy-demanding costs of reproduction in females. Meanwhile, we did not observe stringent differences for the activity of these enzymes in the considered populations of M. soledadinus. Earlier studies on dispersal ecology reported that PGI can be used as a convenient proxy for predicting the dispersal performance of the individuals. This enzyme received intensive focus in invasive species due to its implication in dispersal activity (Niitepõld, 2010;Mitikka & Hanski, 2010). In this study, PGI showed a correlation with residence time, with increased activity in the sampled from the oldest population tested. This pattern may be related to the lower energetic costs of dispersal in this non-flying carabid beetle. The similar enzyme activity does suggest that the potential for energy production by the main core of the energetic metabolism is not altered along the invasion gradient. This finding nicely supports the idea of energetic constraints that must be differentially balanced among the different body compartments according to the ecological conditions experienced by the insect. These data also give strong support to the importance of physiological plasticity as a driver of evolutionary responses in insects (Agrawal, 2001;[START_REF] Chown | Phenotypic plasticity mediates climate change responses among invasive and indigenous arthropods[END_REF].

Phenotyping of adult M. soledadinus sampled from populations distributed along the invasion gradient highlights similarities in the activity of the primary metabolism (enzymatic activities). All populations are close at the Kerguelen Islands, both genetically (unique introduction event a century ago, see Chapter 2) and geographically, and they were sampled in similar microhabitats to smooth as much as possible the effects of micro-environmental variations. Our results demonstrate that energy can be produced in a similar fashion among populations along the invasion gradient. 2016). In further analyses, more in-depth data computation should be developed and used (Cottret et al., 2010), in order to draw metabolic stories by connecting the metabolites that best explain groups separation. We do believe that this is the only way for elaborating the role of these metabolites within each of the proposed invasion gradient scenario.

Chapter 3

Supplementary Material

Tab.1 Summary of the 124 metabolites included in the RDA analysis and corresponding correlation coefficients with each axes of the analysis (RDA1 and RDA2). The first column echoes the metabolite s names used in the correlation circle of the Fig. 11, of which full names and KEGG numbers are displayed in the second and third columns. The bold entries correspond to metabolites plotted in the correlation circle. Chapter 4

-Introduction

Human-mediated invasive species distribution and dispersal have received growing interest over the past few decades, largely due to the significant impact of invasive species on ecosystem services, on the economy [START_REF] Cook | Predicting the economic impact of an invasive species on an ecosystem service[END_REF]Pejchar & Mooney, 2009), and on biodiversity [START_REF] Lockwood | The role of propagule pressure in explaining species invasions[END_REF]. In several cases, it remains unclear whether invasive species are the main drivers of change in community assemblages and ecosystem functioning, passengers benefiting from the ecological alterations of disturbed habitats, or a combination of these two factors (MacDougall & Turkington, 2005). Regardless of the circumstances, the main environmental parameters governing establishment success and subsequent range expansion are case-dependent (Zenni & Nuñez, 2013;Ehrlén & Morris, 2015), most likely due to species-specific survival, reproduction, growth, and recruitment factors.

Interestingly, although current predictions of the changing ranges of non-native taxa are examined with indirect approaches (e.g. species distribution models), the environmental and mechanistic factors driving geographical range expansion are seldom studied directly. For ectothermic species, temperature, and its variation at different temporal scales [START_REF] Colinet | Insects in fluctuating thermal environments[END_REF], trophic resource availability [START_REF] Romanuk | Resource limitation, biodiversity, and competitive effects interact to determine the invasibility of rock pool microcosms[END_REF], and/or relative humidity (RH) and water availability may be pivotal in establishing each species fundamental realised niche.

Demography and dispersal are driven by stage-and size-specific physiological requirements during invasion process. For instance, water availability can shape the distribution of insect species, be they invasive or native (Hoffmann et al., 2003). Decreased water availability, even if it is minor, can hamper insect survival, particularly for polar species (Everatt et al., 2014). In addition to water availability, energy input, critical for sustaining reproduction, growth, development, and vital biological function is often a strong predictor of species distribution and population density (Hawkins et al., 2003). Variation in these abiotic factors can push insects outside their physiological tolerance window, particularly during range expansion. In fact, terrestrial insects may encounter food and water stress during dispersal events. Intensity of these stressors can be biologically significant when nonflying insects must cover high dispersal distances, particularly when the distribution of feeding and drinking areas is patchy.

Insects often encounter restrictive conditions in their (micro)habitats. A range of physiological adaptations to overcome these environmental constraints has been observed in insects (Teets & Denlinger, 2013). Yet, responses mounted by food-deprived insects during active dispersal are relatively limited and roughly consist of anticipatory augmentation in the amount of body stores and/or reduction of energetic demands [START_REF] Rion | Evolutionary biology of starvation resistance: what we have learned from Drosophila[END_REF]. Alternatively, bodily water loss can be counteracted by a broader response arsenal (Benoit, 2010;Teets et al., 2012), including accumulation of osmolytes (polyols, sugars, and amino acids), which has often been reported in desiccation-stressed insects (Crowe et al., 1992;Yancey, 2005). Physiological changes elicited by desiccating conditions can be monitored conveniently by metabolomics analyses (Foucreau et al., 2012;Hidalgo et al., 2013), Tab

-

Discussion

Merizodus soledadinus

Merizodus soledadinus

Chapter 4

by the availability of potential prey consumed by this predatory carabid beetle (Chevrier, 1996;Laparie, 2011). Large marine vertebrate colonies settle on the shore for reproduction and moulting, which results in large organic matter accumulation in the form of faeces and marine vertebrate carrion. Combined with decaying seaweed, this matter represents a tremendous source of organic input, in which invertebrate fauna, composed primarily of saprophagous taxa, thrives (Vernon et al., 1998). Geographic mapping of M. soledadinus distribution at Îles Kerguelen also displayed large populations along watercourses, and negligible to zero adult density in rock fields, peat bogs, and fellfields, for example (see Renault et al., 2015 for complements). In the present study, our objective was to ascertain the importance of starvation and desiccation in the distribution and dispersal paths of this invasive insect species.

Survival durations in the range of 7-55 d have been reported for starved carabid beetles with body sizes similar to that of M. soledadinus (Petersen, 1999;Stone et al., 2001). Our results showed the generalist predator M. soledadinus outcompetes these similarly-sized insects, with the maximum survival-to-food deprivation period reaching 100 d. However, the survival capacity of M. soledadinus Todd and Block (1997) exposed adult M. soledadinus to harsh humidity conditions, with all VPD values higher than 1 kPa. We designed our experimental treatments within the range of ecologically relevant RH conditions. Indeed, mean air RH 10 cm above ground level fluctuates minimally and is maintained at ~75% during the austral summer in the Falkland Islands [START_REF] Bokhorst | Climate change effects on soil arthropod communities from the Falkland Islands and the Maritime Antarctic[END_REF]; at 20 cm above ground level in South Georgia, RH is ~ 50% RH (Ottesen, 1990). The high summer temperatures of 13 °C in the Falkland Islands, and 9 °C in South Georgia result in VPD values of 0.449 kPa and 0.574 kPa,

was
Chapter 4

respectively (Table S1). Environmental data for RH at Îles Kerguelen during the summer months indicated that adult M. soledadinus were frequently exposed to VPD conditions ranging from 0.1 to 0.5 kPa under stones, where individuals often thrive (Table S2). Throughout the year, mean monthly atmospheric RH conditions and temperatures ranged from 40% to 60% and +2 °C to +8 °C, respectively, therefore estimated VPD varied from 0.30 kPa to 0.64 kPa (Table S1 [START_REF] Lombard | Comparative salinity tolerance in native flies from the subantarctic Kerguelen Islands: a metabolomic approach[END_REF]. This pattern reflects reduction in metabolic activity that spares body reserves [START_REF] Rion | Evolutionary biology of starvation resistance: what we have learned from Drosophila[END_REF], resembling entry into a sit and wait strategy (Hervant and Renault, 2002).

Desiccating conditions altered adult M. soledadinus survival capacity quickly. Vital physiological (metabolic) functions collapsed progressively in the 30% and 70% RH conditions, suggesting that aerobic ATP-producing pathways could not meet energetic demands at the organismal level, thus triggering the onset of compensatory anaerobic ATP production. Augmented alanine and lactate levels were observed after 8 h into the 30% and 70% RH treatments, and these metabolites do not accumulate under control conditions (alanine amounts declined at 100% RH). These compounds are well-known anaerobic metabolism end products in insects (Hoback & Stanley, 2001). The presence of alanine and lactate likely point to an increased energetic demand (or shortage) of energy production in adult M. soledadinus. Glucose levels remained consistently high and nearly constant after 4 h and 8

h of exposure at 30% and 70% RH, and glucose-6-P, fructose-6-P, and threonine concentrations peaked at T8. Feala et al. (2007) suggested that increased amounts of threonine and glycolytic sugars in Drosophila melanogaster exposed to hypoxic conditions may signal a loss of metabolic homeostasis. In fact, most M. soledadinus metabolites measured in our study exhibited elevated levels at 30% and 70%

RH after 4 h and 8 h of treatment, which later decreased following 16 h under 70% RH conditions.

Even if several compounds, particularly amino acids and polyols, accumulate in insects facing desiccation stress, none of these compounds appear to be effective osmoprotectants (Yancey, 2005).

Therefore, this pattern may indicate early signs of metabolic dysregulation and, ultimately, the progressive physiological breakdown of dehydrating individuals.

Most amino acids that are directly associated with the tricarboxylic cycle (i.e. asparagine, glutamate, isoleucine, phenylalanine, threonine, and valine) had augmented concentrations in M.

soledadinus following 8 h of 30% and 70% RH treatment conditions. These findings suggest that fluxes Chapter 4 of these amino acids towards the tricarboxylic cycle intermediates were altered, consistent with the generally accepted hypothesis that mitochondrial function is altered in stressed insects (Teets & Denlinger, 2013). Accelerated body water loss in adult M. soledadinus measured at 30% RH might have damaged biomolecules, including membranes and proteins, in turn altering profoundly biochemical reactions and metabolic functions (Potts, 1994), resulting in elevated protein breakdown. Our survival and metabolomic data support the notion that there is a rapid attenuation of physiological functions in adult M. soledadinus exposed to 30% RH for 4h.

Finally, an interesting pattern emerged in regards to trehalose. This disaccharide is known for its capacity to prevent deleterious effects of dehydration; it is biosynthesised from glycogen and serves to protect membranes against desiccation injuries (Elbein et al., 2003). Among all compounds measured, trehalose showed increased concentrations in beetles exposed to 30% and 70% RH conditions for 4 h and 16 h, which paralleled concomitant decreases in glucose levels. Carbohydrate osmolytes like trehalose might have been accumulated in M. soledadinus adults to counteract desiccation-induced stress.

-Conclusion

The present study provided novel insights into the biological requirements of the invasive predatory beetle M. soledadinus at Îles Kerguelen. Our results indicate that this species has a very high tolerance to prolonged starvation. We also confirmed the crucial importance of water availability for adult survival, which is diminished rapidly when RH conditions fall to 70%. Our findings were consistent with a notable presence of this species in moist microhabitats (littoral areas, sheltered watercourses), and protected habitats with slightly elevated RH (e.g. under stones or large wood debris) (Todd & Block, 1997;[START_REF] Chevrier | Characterization of the habitats colonized by the alien ground beetle Merizodus soledadinus at the Kerguelen islands[END_REF]. During range expansion, the significant starvation resistance we detected for M. soledadinus suggests that this species can disperse successfully along pathways where trophic resources are scare, but drinkable water sources are accessible. In localities without water, adults must rely on trophic resources to gain water, and would be expected to exhibit augmented predation rates. In conclusion, our findings indicated that the geographic distribution of M. soledadinus populations is highly dependent on habitat RH and water accessibility (taken up directly or through prey consumption). The results of this study provide valuable information regarding dispersal pathway predictions employed by M. soledadinus and potential future microhabitats suitable for M. soledadinus colonisation.

Chapter 5

Chapter 5

Effects of elevation on the physiology of the invasive carabid beetle

Merizodus soledadinus at the Kerguelen Islands The geographic distribution and abundance of ectothermic species like insects is highly dependent on climatic conditions. In the context of biological invasions, climatic barrier can represent a significant physiological filter hampering invasion success (Williamson & Fitter, 1996;Walther et al., 2002;Charnov & Gillooly, 2003). Ongoing rising air temperature may favour human-assisted long-distance jumps of exotic insects and subsequent establishment in the release geographic area [START_REF] Roques | Direct impacts of recent climate warming on insect populations[END_REF]. Altitudinal and latitudinal range shift responses to climate changes have been documented for several taxa (Chown & Klok, 2003;Hickling et al., 2006). This is particularly true for insects transported from warmer to cooler regions. In fact, survival and capability to thrive into the released geographic region can be significantly affected by climate change (Hellmann et al., 2008).

Rapidly changing climatic conditions in polar regions therefore increase the opportunities for exotic insects to successfully establish (Frenot et al., 2005) et al., 2011). These climatic changes have long been suspected as important environmental parameters assisting the invasion success of several exotic insects. Among these, the predaceous carabid beetle

Merizodus soledadinus is the only invasive insect originating from the southern cold temperate area;

this insect is native from Patagonia and Falkland Islands (Jeannel, 1962;Roux & Voisin, 1982). The austral origin of the carabid insect raises the question of the physiological thermal limits of this insects and its capabilities to withstand lower or higher climatic conditions of other subantarctic archipelagos where its accidental transportation could be facilitated from the Kerguelen Islands (namely Crozet, Amsterdam & Saint Paul). Altitudinal transects represent a convenient manner to address this assumption, as a fall of 0.5 -1.0 °C usually occurs every 100 m of increase in altitude at the subantarctic islands (Jenkin, 1975).

As its biogeographical native region suggests, this wingless predator is pre-adapted to the cold oceanic climate encountered at the Kerguelen Islands, and previous studies highlighted a strong tolerance to increased temperatures [START_REF] Lombard | Comparative salinity tolerance in native flies from the subantarctic Kerguelen Islands: a metabolomic approach[END_REF]. Monitoring records reveal an

Chapter 5 accelerated range expansion from the introduction site (Lebouvier et al., 2011), and a distribution along coasts and inland rivers (Ouisse et al., 2016), probably because trophic resources (terrestrial invertebrates) are abundant nearby marine vertebrates colonies, and decreased in inland habitats.

Monitoring records of geographical distribution and characterization of habitats colonized by M.

soledadinus showed recent altitudinal expansion [START_REF] Chevrier | Characterization of the habitats colonized by the alien ground beetle Merizodus soledadinus at the Kerguelen islands[END_REF]. These authors highlighted that M. soledadinus can now be found up to 400m above sea level (asl), despite a priori unfavourable conditions in altitudinal habitats. Indeed, elevation quickly leads to scarcer availability of trophic resources and temperature decrease (Machac et al., 2011;Hoiss et al., 2012). Studying and comparing highland and lowland populations of M. soledadinus would allow to understand biotic and abiotic conditions required for colonisation process, and could allow gaining insights into the effects of climate change, and particularly raising temperature, on the invasive success of this ground beetle.

This study aims to investigate the effect of higher elevation on body size and metabolism of adult M. soledadinus. Adult M. soledadinus were sampled nearby Molloy and St Malo, where the ground beetles could easily be found up to 250 m above the sea level, the limit after which densities were too low to sample. A flat transect (straight line transect orthogonal to the sea shore) was conducted nearby the research station, to take into account the reduction of the number and diversity of trophic resources, and their possible impact on body size and stores. This flat transect thus allows to distinguish the distribution of trophic resources from the altitudinal effect. Morphological traits were measured, as well as total concentrations of three general reserve compounds in insects (proteins, triglycerides and glycogen) via colorimetric assays. Metabolic fingerprints, through Gas Chromatography -Mass Spectrometry analysis, were compared between each transect and elevation.

We hypothesise that the reduction of the temperature along elevation gradients should result in a reduction of (i) the body size of individuals, (ii) the amount of body reserves and (iii) the metabolic phenotypes. , 50, 100, 150, 200, 250, 300 and 400 m inland). At each sampling point, GPS coordinates were recorded, and a total of 86 adult M. soledadinus were collected: 50 insects were sampled for morphometrics and colorimetric assays (total protein and glycogen), 18 insects (six replicates of three pooled beetles) were collected for triglyceride assays, and 18 insects (six replicates

-Material and Methods

Chapter 5

of three pooled beetles) were collected for Gas Chromatography/Mass Spectrometry (GC-MS)

analyses. After collection, insects were directly plunged into microtubes containing 1 mL of 96°

ethanol and stored at -20 °C before being further analysed. The physiological status of the specimens may vary from one day to the next, depending on temperature, precipitations or trophic status of the insect. For GC-MS and triglyceride analyses, each replicate was composed of three individuals caught in the morning only on two consecutive days to average environmentally-induced noise and limit possible effects of circadian rhythm on the physiology of the insects. Finally, all samples were done during the same period, and we paid particular attention at the meteorological conditions to avoid having climatic differences among the sampling days. 200 µL of Triton-BSA buffer and incubated 10 min at 60 °C just before the assays. Manufacturer s instructions were followed for the triglyceride colorimetric assays (Triglycerides, kit reference CC02200, LTA srl, Italy).

d) GC-MS analyses: sample preparation and derivatisation

Concentrations of non-structural carbohydrates, polyols, amino and organic acids were measured using a Gas Chromatography/Mass Spectrometry (GC-MS) platform as described in Khodayari et al. Then, 1 µL of each sample was injected using the split mode (25:1). We used the same GC-MS procedure and settings as in Khodayari et al. (2013). Calibration curve samples for 62 pure reference compounds at 1,2,5,10,20,50,100,200,500,750,1000 and 1500 µM concentrations were run.

e) Statistics

The samples collected at the foreshore level will be further referred to as initial sampling point . For each transect, the Euclidian distance between the initial sampling point and each other sampling point was calculated from the georeferenced coordinates. For both altitudinal transects, Molloy and St Malo, altitude and distance in between the initial sampling point and other sampling points were highly correlated (r = 0.94, P < 0.001). At Anse des Papous, altitude did not vary, so only the parameter distance was kept as explanatory variable in our statistical analyses. The location of each transect (Papous, Molloy and St Malo) was also added to distinguish site effects.

We examined the effects of sex, transect and distance to the initial sampling point on the five morphological traits measured in adult M. soledadinus. As a general measure of body size, we used the coordinates of each individual on the first axis of a Principal Component Analysis (FactoMineR package, [START_REF] Lê | FactoMineR: an R package for multivariate analysis[END_REF], which counted for 67.4% of the total variance.

Chapter 5

Linear mixed-effects models (nlme package, Pinheiro et al., 2007) were used to assess the effect of transect, distance to the initial sampling point and sex on our measured variables, with a random effect of sampling points. According to AICc results (the models are presented in Tab. 1), the most significant model for each variable (body size, protein, glycogen and triglyceride amounts) was retained among six proposed models.

Tab. 1 Set of explanatory variables included for model selection procedure (AICc)

A total of 46 metabolic compounds were identified via the GC-MS procedure. Concentrations were homogenised (nmol.mg -1 of individual dry mass) and four molecules (cadaverine, ornithine, quinate and ribose) showing overly high to low concentrations in various samples were removed from subsequent analyses. First, we tested the effects of transect, distance to the initial sampling point, and their interactions on individual metabolite concentrations. MANOVAs were performed to test for potential differences among experimental groups. Second, total metabolite amount of each chemical family was summed for each experimental condition (Free Amino Acids, FAA, N = 13 metabolites;

Intermediate Acidic Metabolites, IAM, N = 10 metabolites; Polyols, N = 8 metabolites; Sugars, N = 5 metabolites and Amines N = 4 metabolites). Only two molecules were not included inside families:

gluconolactone and glycerate involved in the pentose phosphate pathway and the glycolysis, respectively. Linear Models were then used to compare the calculated amounts for each metabolic family according to the transect and the distance to the origin point. Third, linear discriminant analyses (MASS package, Venables & Ripley, 2002) were run on metabolites sharing less than 80% correlation (N = 27 metabolites). Statistical significance of discrimination was confirmed using Monte-Carlo permutation test (P < 0.001; 10 000 permutations). In a first LDA, we plotted the metabolic phenotypes of adult M. soledadinus from the three transects. This LDA revealed that our dataset of 27 metabolic compounds was better discriminated transect by transect, with the total variance explained by the first axis at 52.1% (the between-group inertia being 10.7 times higher than the within-group inertia), and by the second axis at 47.8%. LDA analyses were then performed separately. Statistical analyses were performed on log-transformed data to improve adequacy of models residuals to normal distribution, which was checked using QQ plots and Shapiro-Wilk tests for multivariate normality.

All analyses were realised with R™ 3.3.0 statistical software (R Core Team, 2016).

1 2 3 4 5 6 Distance from the origin point X X X Transect X X Sex X X Distance x Location X X Distance x Sex X X
Chapter 5

-Results

a) Morphological changes along the transects

The statistical model with the lowest AICc value for explaining variations in body size among Chapter 5

Metabolic variations were further examined for each transect in order to assess if similar discrimination of the sampling groups occurred. For the transect conducted at Anse des Papous, the first axis of the LDA (37.2% of the total variance) separated the samples collected at 0 and 400 m inland from the samples collected at 100 and 200 m inland (Fig. 10.a). This discrimination was partly explained by higher amounts of galactose and glycerol-3-phosphate in the two latter sampled groups. The second axis (34.7% of the total variance) sorted the groups according to the distance to the sea. This axis was mainly supported by pipecolate and succinate whose concentrations increased in groups closest to the sea versus higher mannitol concentrations in groups the farthest to the sea.

For the LDA on the Molloy transect (Fig. 10.b), the second axis (24.5% of the total variance) opposed groups sampled at 0 and 100 m asl from those sampled at 150 and 250 m asl, with regularly increasing concentrations of galacturonate and pipecolate. The 150 and 250 m asl sampling points are opposed on the first axis (27% of the total variance), reflecting the peak in concentrations of fructose, glycine or malate at 150m compared with higher elevations. On both axes, the groups sampled at 50m and 200m asl overlapped.

In the second altitudinal transect (St Malo, see Fig. 10.c), the first axis of the LDA (26.2% of the total variance) tended to separate the sampling groups according to the altitudinal gradient. The second axis (22.6% of the total variance) discriminated the 200 m asl sampling group from the others, due to increased amounts of arabinose and mannitol.

-Discussion

The carabid beetle Merizodus soledadinus is one of the most successful invasive insect at the Kerguelen Islands (Lebouvier et al., 2011;Ouisse et al., 2016). Its geographic distribution has long been restricted to coastal areas [START_REF] Chevrier | Characterization of the habitats colonized by the alien ground beetle Merizodus soledadinus at the Kerguelen islands[END_REF], but since the early 2000 s, it is sampled at an increased frequency along altitudinal gradients in this archipelago. In the present study, we speculated that the ongoing colonisation of altitudinal habitats since the past decade has been facilitated by changes in climatic conditions that occurred at the Kerguelen Islands (Lebouvier et al., 2011). The geographic distribution of M. soledadinus at the Kerguelen Islands also represents a good opportunity for assessing the effects of microhabitat conditions and thermal gradients on the morphology, biochemistry and physiology of field-sampled specimens.

Body size of insects is expected to increase over altitudinal gradients, as a result of colder thermal conditions. This pattern of body size variation has been conceptualised as the Bergman s and temperature-size rules (Atkinson, 1994). Consistently, Chown and Klock (2003) reported a significant augmentation of the body size of four weevil species sampled along a 1000 m-altitudinal gradient at the subantarctic Marion Island, whose seasonal climatic conditions are similar to those of the Kerguelen Islands. However, we did not observe this allometric relationship in adult M. soledadinus, and body sizes of this carabid beetle were even decreased at higher altitudes. In spite of the above transects: starting from grassland dominated by Poa annua at sea level, it shifted to continuous cover of Acaena magellanica at middle-hillside, which progressively became scarcer and patchy in rocky fell-fields at 250 m asl. Changes in vegetation cover are known to impact the structure and diversity of invertebrate communities (Gremmen et al., 1998), in turn affecting trophic resources qualitatively and quantitatively for both larva and adults of M. soledadinus. Yet, a nearly constant body size was measured in carabid beetles from the straight line transect, which was designed to assess the effects of decreased availability of trophic resources as a function of the distance to the sea. As a result, decrease of trophic resources does not necessarily affect body size significantly in adult M. soledadinus, and nutrient availability is not the exclusive cause of the smaller body sizes measured in elevated habitats.

Temperature is expected to decrease from 0.50 to 1.0 °C when elevation increases by 100 m at the subantarctic islands (Jenkin 1975), with the rate of thermal decrease being the highest from 0 to 150 m asl (Davies & Melbourne, 1999). This suggests that temperature was decreased by 1.5 to 2.5 °C from the sea level to the highest sampling point in our experimental design. At 5 m asl at the Kerguelen Islands, mean monthly temperatures measured 10 cm below the ground level, where this carabid beetle thrives, vary from ca. 1.2 to 8.4 °C from winter to summer (Lalouette et al., 2012). Mean monthly temperatures are lower than 3.8 °C during six over 12 months, and lower than 2.4 °C during 4 months (Lalouette et al. 2012). These data suggest that M. soledadinus sampled above 150m asl spend a significant part of the year at temperatures around 0 -1 °C. These thermal conditions are highly restricting for this insect whose acute thermal sensitivity has been reported in earlier investigations (Lalouette et al., 2012;[START_REF] Lombard | Comparative salinity tolerance in native flies from the subantarctic Kerguelen Islands: a metabolomic approach[END_REF]. Indeed, metabolic activity and efficiency of adult M. A range of studies reported decreased in development rates in insects of smaller size when energy assimilation is restricted (Partridge & French, 1996;Moczek, 1998;Nijhout, 2003;Mirth & Riddiford, 2007). During development, the rate of growth of insects is partly driven by protein synthesis (van der Have & de Jong, 1996), and this enzymatically-based process should work more slowly at lower temperatures and/or should be tone down when resources are limiting. There was no significant effect of the type of transect on protein and glycogen contents, but body proteins were significantly reduced in females along altitudinal transects, which, in addition, were characterised by a reduced body size. This finding supports the idea of the strong importance of thermal-imposed resource limitations in altitudes. Finally, triglyceride contents were decreased along the three transects, which could depict energetic adjustments according to the nature of preys available. Diet-Chapter 5 related differences have already been measured in adult M. soledadinus fed with enchytreids or fly maggots (Laparie et al. 2012); carabid beetles food-deprived for two days before being refed with fly maggots exhibited higher triglyceride amounts.

Environmental metabolomics has been proven a powerful tool allowing to delineate insectenvironment interactions (see reviews by Viant, 2008;[START_REF] Bundy | Environmental metabolomics: a critical review and future perspectives[END_REF]. Field-sampled organisms are expected to show high inter-individual variability, which we attempted to smooth by working on pools of three insects. The global inter-site comparison revealed that insects from the three populations (Anse des Papous, Molloy and St Malo) were characterised by distinct metabolic phenotypes, despite a relatively small geographic distance separating the three sampling sites.

Interestingly, metabolic phenotypes of the specimens from the two altitudinal gradients (Molloy and St Malo) did not overlap, suggesting that insects experience distinct ecological situations along these two gradients. Indeed, we have no genetic data for these three populations, but genomic analyses revealed that allelic diversity is rather similar in specimens among populations of M. soledadinus sampled along the invasion gradient (see Chapter 1).

Several amino acids, including the essential isoleucine, leucine, methionine, phenylalanine, threonine and valine, were characterized by higher amounts in the straight line transect as compared with the two altitudinal gradients. Essential amino acids cannot be synthesized by insects and are only acquired from trophic resources, suggesting higher food intake in adult M. soledadinus from the straight line transect. Nutrient limitation in essential amino acids can greatly constrain females fecundity (O Brien et al., 2002), as these metabolites contribute for a significant part of egg carbon.

The speculated higher food intake of adult M. soledadinus from the straight line transect is consistent with the variation of protein concentration in females, which remained constant (or even increased) in this transect, whereas it was reduced in the altitudinal transects. Moreover, amino acids represent a prominent source of nitrogen for insects, and nutrient limitation during larval stage can have beetles can thrive in the surroundings of sea wrecks where the salinity level can be high (from 35 to 70 parts per thousand). Saline environments impose osmoregulatory constraints to organisms, which can be supported by accumulation of specific osmolytes (Yancey, 2005). The accumulation of inositol and pipecolate were already observed by (Hidalgo et al., 2013) in adult M. soledadinus experimentally exposed to increasing salty conditions. Specimens sampled 400 m far from the seashore had lower amounts of amino acids, TCA cycle intermediates and sugars as compared with the three other groups.

Even if we have no data for the metabolic rates of these specimens sampled 400 m far from the seashore, this observation might suggest a lowered metabolic activity resulting from nutrient limitation. Three metabolic families were found in lower amounts in altitudinal transects, with no effect of the distance to the initial sampling point (namely free amino acids, intermediate acidic metabolites and amines), this pattern being similar as the one recorded for body size variations, and, similarly to the 400 m sample from the straight line transect, may reveal reduced metabolic activity.

Even if different metabolites were involved into the discrimination of the groups of the two altitudinal transects, the general picture was rather similar. Specimens sampled along the seashore differed from the other samples, and those sampled at 200 (St Malo only) and 250 m asl were largely opposed. In this latter group, there was a slight tendency of augmentation of the amounts of circulating amino acids, intermediate acidic metabolites and polyols. This pattern has been reported earlier in a large range of cold-exposed insect [START_REF] Colinet | Water relations, fat reserves, survival, and longevity of a cold-exposed parasitic wasp Aphidius colemani (Hymenoptera: Aphidiinae)[END_REF]Lalouette et al., 2007), including in adults of M. soledadinus (Laparie & Renault, 2016). Higher amounts of free amino acids represent signs of cold stress in insects, thus adding another evidence of the restrictive thermal conditions for the physiology of adult M. soledadinus at 200 -250 m asl. The discriminant analysis of the two altitudinal transects, St Malo and Molloy, also revealed a similar ranking of the sampling sites, with a gradient of lower elevation toward higher elevation sites along the first axis. It can be suggested that this pattern stems from the same factor acting upon individual s physiology in the two altitudinal transect, which is probably temperature. At intermediate elevations, metabolic phenotypes exhibited important intersite variations, most probably resulting from the specific micro-environmental characteristics of these habitats. Inter-individual variance (age, sex, reproductive status, nutritional status at the time of the collect) may explain the high within-group variance, as well as potential divergence in origin due to high dispersal abilities of this ground beetle: an individual collected on a transect may not have spent all its life at the same level and may have reached lower of higher elevation after its emergence (larvae have much lower dispersal abilities compared with adults). This phenomena might have blurred some of the results but our findings at higher investigation scales suggest it is not as frequent as to smooth all patterns along transects.

-Conclusion

This study highlights the phenotypic changes of adult M. soledadinus sampled along terrestrial and altitudinal gradients at the Kerguelen Islands. Body size of adults were reduced as altitude

Chapter 5

Supplementary material

Tab. S1 GPS coordinates of the sampling sites along each of the three transects soledadinus was conducted at the Kerguelen Islands [START_REF] Chevrier | Characterization of the habitats colonized by the alien ground beetle Merizodus soledadinus at the Kerguelen islands[END_REF]. Results emphasised humid habitats as one key element of the insect s realised niche. In a third study, we thus quantitatively evaluated how water availability and trophic resources governed the spatial distribution of this invasive predatory insect on the Kerguelen Islands (Chapter 4). Specifically, expected survival time under food and water stress (relative humidity conditions of 100%, 70%, and 30% RH) and changes in a set of primary metabolic compounds induced by such stresses (GC-MS, metabolomics) were determined. We found that adult M. soledadinus supplied with water ad libitum were highly tolerant to prolonged starvation (LT50 = 51.7 ± 6.2 days). However, food-deprived insect survival rapidly decreased at moderate (70% RH, LT50 = 30.37 ± 1.39 hours) and low (30% RH, LT50 = 13.03 ± 0.48 hours) relative humidity conditions. Consistently, body water content rapidly decreased in insects exposed to 70% and 30% RH. Metabolic variation emphasised the effects of food deprivation in control insects (exposed to 100% RH), in which a progressive decline of most glycolytic sugars and TCA cycle intermediates was observed. Overall results of our study indicated that the geographic distribution of M. soledadinus populations is highly dependent on habitat relative humidity and water accessibility (directly available for the insect or through prey consumption). suggest that this pattern could be attributed to the lower thermal conditions experienced by juveniles during developmental period in altitude. Concerning body reserves, glycogen amounts remain similar along the three transects, the protein amounts decreased in females sampled farther from the seashore and increased levels of triglyceride were found in individuals sampled in altitude. Metabolomics analyses allowed to quantify 42 free-circulating metabolites and the resulting metabolic phenotypes distinguish samples from the sea shore from those sampled at 200m asl. This difference probably results from the saline conditions encountered at the sea shore, which requires increased levels of osmoprotective compounds. We concluded that thermal conditions encountered in altitudinal habitats are suboptimal for adult M. soledadinus, but ongoing climate seems to assist the colonisation of these habitats, provided that biotic requirements match.

-

Other experiments conducted during this thesis, but not included in the dissertation Several other experiments were run during the three years of this PhD, but are note presented into this manuscript. These works can be combined into three main studies.

1/ We used molecular approaches (13 microsatellite markers) to examine kinship structure in adult M. soledadinus at a fine geographic scale. Six hundred and thirty nine individuals were sampled in 2010 at the locality of Cataractes, along a 1500m transect parallel to the seashore. Sampling sites were spaced by increasing intervals (0m, 10m, 50m, 100m, 250m, 500m, 1000m and 1500m) At each sampling point, individuals were collected under c.a. eight different stones. Kinship reconstructions along this transect will allow to understand the dispersal dynamics of M. soledadinus at a small scale (Ouisse, Guiller, Renault, data not presented). This experiment is a remake from a study described in Lalouette (2009) whose 85m transect was insufficient for drawing conclusions. Microsatellites markers are already genotyped, the dataset needs now to be analysed (Coancestry software).

2/ During range expansion, individuals from front populations are predicted to exhibit differences in stress response because of their more frequent exposure to novel environmental conditions (and potentially new stressors). We designed an experiment to explore this assumption, by exposing individuals (10 replicates of 10 beetles per population) sampled from six populations at the Kerguelen Islands (residence times of 103,36,21,10,6 and 4 years since local establishment) to stressful conditions. Specifically, we tested the effects of desiccation (similar procedure as described in Chapter 4), starvation (similar procedure as described in Chapter 3) and fluctuating thermal regimes (from 8 °C to 28 °C with a stepwise increase/decrease of temperature during daytime, [L:D 12:12], and constant 8 °C condition at night). In an additional experimental condition, individuals were exposed to all of three environmental factors simultaneously. While these words are written, this experiment is still running at the research station of Port-aux-Français (Ouisse, Hotte, Renault, data not presented). to corroborate the hypothesis of the single introduction event of this species (Chapter 2). Together with the long term monitoring of the terrestrial biodiversity, genetic results confirmed the chronosequence of the geographical expansion of this insect at the Kerguelen Islands.

Evidence accumulates for progressive phenotypic changes along the invasion gradient of M. soledadinus, and these changes are likely imputable to spatial sorting (Chapter 3). The biological and ecological data collected for M. soledadinus (Laparie et al., 2010(Laparie et al., , 2013;;[START_REF]Sea water transport and submersion tolerance as dispersal strategies for the invasive ground beetle Merizodus soledadinus (Carabidae)[END_REF]Lalouette et al., 2012;Hidalgo et al., 2013;[START_REF] Chevrier | Characterization of the habitats colonized by the alien ground beetle Merizodus soledadinus at the Kerguelen islands[END_REF][START_REF] Lombard | Comparative salinity tolerance in native flies from the subantarctic Kerguelen Islands: a metabolomic approach[END_REF]; Chapter 1, 4 and 5) are essential pieces of the puzzle for our understanding of the population dynamics, potential invasion routes and ecological niches of this invasive insect at the Kerguelen Islands. This knowledge could be further used to parametrise range expansion models to predict the future expansion of M. soledadinus on the Kerguelen territory, and propose mitigation measures. For example, in the case of the invasion of Australia by the cane toad, authors used ecological information, anthropological elements and climatic conditions of the current distribution of Rhinella marina to predict the extent of habitats that could be invaded by this species (Sutherst et al., 1996;Urban et al., 2007).

Considering the data that are now available for M. soledadinus, we suggest that the combination of distributional, genetic and ecological data could allow to create a resistance matrix that would indicate the most favourable habitats together with the least cost paths to join them at the Kerguelen Islands. Such a model could help predicting the extent and the expansion rate of M. soledadinus, in this archipelago. This model should primarily include the topography of the Kerguelen Islands, as we know that M. soledadinus can only be found up to 400m asl at present. Altitudinal habitats are currently physiologically constraining (Chapter 5) for this insect, meaning that this kind of habitats would be attributed increasing cost values when elevation increases. Also, this ground beetle has a coastal distribution and low tolerance to desiccation (Chapter 4). The model should thus accounts for increased habitat values farther from the sea or major watercourses. Like in other cases of biological invasions (Thomas et al., 2001;[START_REF] Butin | Adaptation during biological invasions and the case of Adelges tsugae[END_REF]Mau-Crimmins et al., 2006), modelling the distribution of M. soledadinus in the invaded areas could help to understand the mechanisms underlying geographic expansion and to predict future directions of the ongoing expansion. From a practical standpoint, this would greatly help stakeholders to undertake localised conservation measures in this nature reserve (Réserve Naturelle des Terres Australes Françaises).

At the Kerguelen Islands, individuals of M. soledadinus have no apparent competitors.

Nevertheless, a high level of intra-specific competition occurs in microhabitats where population density is very high (more than 400 individuals can be found in less than 10 minutes, pers. obs.). Under controlled conditions, cannibalistic interactions were observed among adults, but also between adult Méthodologie : la durée de vie des adultes a été déterminée grâce au maintien en conditions contrôlées de 500 individus prélevés juste après leur émergence (cuticule rouge). Un proxy de la fécondité a été estimé en disséquant des femelles prélevées tous les mois sur une période de 18 mois et en comptant les oeufs. La quantité de réserves a été estimée au cours des mois grâce à des analyses colorimétriques.

L activité des individus au cours de l année a été analysée à partir d un jeu de données rassemblant 10 ans de piégeage à proximité de la base de Port-aux-Français (pots barber, 2005-2015).

Résultats : les adultes M. soledadinus vivent en moyenne 8 mois, mais leur longévité peut s étendre jusqu à plus de 14 mois en conditions contrôlées. Les femelles disposent en moyenne de 8 oeufs dans leurs ovarioles, de manière constante au cours des mois, sans période notable de ponte. Les données de piégeage montrent que les adultes sont actifs toute l année, avec un léger pic de capture pendant l été austral. Les réserves corporelles restent relativement stables au cours de l année, suggérant que les individus continuent à se nourrir pendant l hiver, potentiellement avec des proies différentes qu en été. ABSTRACT Global trade and human movements increase the likelihood of long-distance transportation of propagules and their subsequent introduction into new geographic regions. In some instances, newly established species can become dominant in invaded communities, at the expense of native species. Besides threatening invaded communities and ecosystem functions, biological invasions constitute natural experiments that allow to study eco-evolutionary processes in real time, including the occurrence of new biotic interactions affecting community composition, rapid adaptation to novel environmental conditions, or dispersal evolution at range margins. Because of their impoverished native communities, oceanic islands ecosystems are particularly sensitive to biological invasions, and the French subantarctic islands are no exception. For instance, the flightless predatory carabid beetle Merizodus soledadinus is native from the southern tip of South America, and has been accidentally introduced to the Kerguelen Islands in 1913.

Conclusion

In the present work, we aimed at understanding the main mechanisms underlying the invasive success of this insect at the Kerguelen Islands. Using a vast array of methodologies, ecological features of M. soledadinus were investigated with analytical procedures scaling from population to molecule through the individual level. Genetic investigations support the historically-based hypothesis of a single introduction event at a unique location of the Kerguelen Islands.

No genetic structure was observed among individuals sampled from different populations along the invasion gradient.

We tested the hypothesis of spatial sorting of populations during range expansion, by exploring phenotypic changes among individuals sampled along the invasion gradient. The measured phenotypic traits revealed major differentiation of adults according to the residence time of their populations, confirming the occurrence of spatial sorting of populations during geographic expansion. We also demonstrated that the geographic expansion of M. soledadinus, and microhabitat selection, are primarily governed by the availability of water resources, as suggested by the high sensitivity to water stress of adults of this ground beetle. In parallel, colonisation of altitudinal habitats is governed by thermal conditions, which seem to be physiologically constraining from 200m asl onwards. As the altitudinal distribution of M. soledadinus still extends, we concluded that ongoing climatic changes play a pivotal role in this expansion. Finally, adults of this ground beetle are long-lived and active year-round. The ecological knowledge of M. soledadinus characteristics and spatial expansion dynamics suggest that the colonisation process of the Kerguelen archipelago by this species will continue. Altogether, these data could be used for parametrising range expansion models that would delineate dispersal pathways and expansion rates, in the objective to assist stakeholders management decisions.

  associated concepts a) Terminology and concepts of the invasion process b) Going further than invasiveness and invasibility c) Ecological and evolutionary factors driving the invasion success / failure d) Contributions to the understanding of the invasion process from evolutionary biology e) Dispersal of range expanding specimens 2 -Presentation of the studied system: a ground beetle invading the French subantarctic Kerguelen Island a) The subantarctic region, geographic context b) Differences and similarities of subantarctic islands c) Human presence and impacts d) The Kerguelen archipelago e) Relevance of subantarctic islands in ecology f) Merizodus soledadinus: Taxonomy and distribution g) Our current knowledge of the biology of M. soledadinus Introduction 2 -Material & Methods a) Estimation of adult longevity b) Annual activity in natural environments c) Reproductive status of females along the year d) Annual variations of body stores e) Statistical analysis 3 -Results a) Estimation of adult longevity b) Annual activity in natural environments c) Reproductive status of the females along the year d) Annual variation of body stores 4 -Discussion Chapter 2 -Biogeographic reconstruction and populations genetics of the invasive carabid beetle Merizodus soledadinus genetics of M. soledadinus at the Kerguelen Islands 4 -Discussion a) Biogeography b) Population genetics of the carabid beetle M. soledadinus at the Kerguelen Islands Chapter 3 -Large-scale phenotyping along the invasion gradient of the carabid beetle Merizodus soledadinus at the Kerguelen Islands The importance of relative humidity and trophic resources in governing ecological niche of the invasive carabid beetle Merizodus soledadinus in the Kerguelen archipelago of starvation and desiccation on survival durations b) Changes in body water content due to RH c) Metabolic fingerprinting

  changes along the transects b) Variations in protein, glycogen and triglyceride contents cbut also some limitations a) What about the other developmental stages, and more particularly larvae? b) Inter-individual variability c) What does M. soledadinus eat? d) Range expansion of M. soledadinus: a conservation issue

  Fig. 1

Tab. 1 .

 1 Summary of geographical, physical, ecological and historical variables of subantarctic islands and cold temperate islands. Islands of the same archipelago are connected by Subantarctic islands fauna host higher proportions of Human presence and impacts century and the 1850 s.

  Fig. 4

  Fig. 7

Chapter 1 Fig. 1

 11 Fig. 1 Localisation of the sub-Antarctic Kerguelen archipelago. Merizodus soledadinus was uniquely introduced at Port Couvreux. All the experiments were conducted at the research station of Port-aux-Français, and beetles were sampled in the vicinities of the research station Recent studies on Kerguelen Islands described the autecology of M. soledadinus specimens exposed to a range of environmental factors. These works reported the physiological plasticity and tolerance of this insect to thermal variations, including temperature (Lalouette et al., 2012; Laparie &

Fig. 5

 5 Fig. 2 Merizodus soledadinus a

  Fig. ESM_1

  Fig. ESM_2Merizodus soledadinus

  Fig. 1

Fig. 2

 2 Fig. 2 Structure outputs for RAD-seq data from adults of M. soledadinus sampled in Patagonia (native geographic area), South Georgia and Kerguelen Islands (introduced areas, with first estimated introduction in 1963 and 1913, respectively). The proportion of assignation (vertical axis) of each individual (vertical bars) is presented for K=2 and K=3 population clusters Genetic differentiation of the specimens from the three biogeographic area is also outlined by pairwise FST values between the three populations. A stronger differentiation was observed between Patagonia and South Georgia (FST =0.1), or between Patagonia and Kerguelen Islands (FST =0.12) than

  Fig.3M. soledadinus

  Fig.7M. soledadinus

-

  have been stopped rapidly, all of them being now concentrated at Ratmanoff. Multiple introduction events from Port-aux-Français could explain greater genetic diversity at Ratmanoff, where individuals were first observed around 2008. Individuals sampled at Val Studer show reduced genetic diversity, and a positive inbreeding coefficient. We hypothesised that this recently established population could either result from anthropogenic introduction from the research station, or from natural dispersal from the north coast (Port Elizabeth). To tackle this assumption, individuals from the intermediary site of Val Studer North Chapter 2 were included into our analyses, to evaluate the possible arrival of M. soledadinus from the north (Port-Elizabeth). Our data confirmed this range expansion path, revealing inland colonisation from the north coast, and also suggest that the inland population of Val Studer was probably introduced by humans To conclude, M. soledadinus invaded most of the eastern part of the Kerguelen archipelago in roughly 60 years. The geographical expansion is now growing faster, possibly as a result of spatial sorting, human transportations, increased beetle s demography and climate change. These results seemingly cast a dark shadow on the native arthropod communities of the western, still uncolonized, part of the archipelago, which could soon glimpse the moving tips of Merizodus antennas. To complete this study, we will have to incorporate additional data so that the biogeography of this species will be completely covered, and thus even better understand population dynamics of M. soledadinus at the phenotyping along the invasion gradient of the carabid beetle Merizodus soledadinus at the Kerguelen Islands T. Ouisse, F. Hendrickx, D. Renault In prep. Highlights -Characterisation of several morphological, behavioural and physiological traits in populations sampled along the invasion gradient -Individuals sampled in localities recently colonised have different morphology, locomotor activity, starvation resistance and metabolite amounts than individuals from formerly established populations Results from this new integrative approach show distinct phenotypic differentiation depending on the residence time of populations, possibly explained by spatial sorting Introduction Biological invasions have become a central research theme in ecology and evolution over the past decades (Handley

  Fig.1M. soledadinus

  ) to describe morphometric variations along the invasion gradient. MANOVAs were used to assess the potential relationship between residence time and size of the measured morphometric traits. In these analyses, the sex was included into the explanatory variables. The normality of residuals was verified with QQplots and Shapiro-Wilk tests. Factorial Discriminant Analyses (MASS package, Venables & Ripley, 2002) were performed on separated sex to investigate morphological variations at the intra-population level, and changes among populations. For each sex, a morphological distance matrix was built from the score value of each individual along the first axis of a Canonical Discriminant Analysis (CDA, candisc package, Friendly & Fox, 2013

  Fig.4M. soledadinus

Fig. 8 -

 8 Fig. 8

  scale however, metabolomic investigations show that populations were characterised by distinct metabolic phenotypes depending on the sex first and residence times of the populations. The results seems to indicate a greater inter-replicate/intra-population variations in females than males. This may be explained by differences in the reproductive status of the samples, as the presence and number of eggs can greatly modify the contents in proteins and lipids of whole-body extracts. Population of similar residence time (more than 35 or less than 10 years since establishment) are grouped together in the analysis, indicating general distinct metabolic phenotypes of populations at the invasion front compared with formerly established populations. This preliminary conclusion is different from the work ofTracy et al. (2012). These authors described the spatial sorting of Rhinella marina, which displays distinct morphological and behavioural patterns along the invasion wave, without physiological distinctions highlighted in the different dispersal-related traits investigated. However, specific investigations are required to further interpret this metabolomics dataset. The next step consists in delineating specific metabolic pathways that could be different between populations according to their residence time.The amount of results provided by this study highlight that distinct phenotypic traits are affected by residence time of populations, demonstrating the existence of spatial sorting. Fine scale metabolic inquiries are required to help understanding the underlying mechanisms of phenotypes differentiation, as well as to elucidate physiological trade-offs favouring dispersal at the invasion front.Physiological adjustments to environmental variables occur at several levels of organisation, all being sustained by the metabolic network (production of energy and primary and secondary metabolites which are important bricks for physiological remodelling). Increased energetic demand associated to elevated performance of one trait modifies global metabolic network operations(van Petegem et al.,

  Fig. 1 M. soledadinus ad libitum

  Fig.4M. soledadinus

T-

  . Ouisse, E. Day, L. Laville, F. Hendrickx, D. Renault In prep. Highlights -M. soledadinus extends its geographic range toward altitudinal habitats, where individuals are exposed to lower thermal regimes and decreased trophic resources, both of which affecting insect s physiology -Wild individuals were sampled along two altitudinal gradients and along a flat transect (orthogonal to seashore, accounting for decreased trophic resources availability) and we measured morphometric traits, body reserve compounds and free-circulating metabolites contents Individuals from altitudinal transects have smaller body size, increased amounts of triglycerides and increased amounts of compounds usually represented in cold-exposed insects (above 200m asl only); females sampled farther from the sea have decreased amounts of protein -Altitudinal habitats are constraining to adult M. soledadinus, probably because of the lower temperature. Ongoing climate change at the Kerguelen Islands may favour further range expansion of this species Introduction

  environmental gradients Adult M. soledadinus were hand-collected under stones in March 2013 at the Kerguelen Islands at three distinct localities: Molloy, St Malo and Anse des Papous (see Fig. 1 and supplementary Tab S1). At Molloy and St Malo, two altitudinal transects were realised and started from the foreshore (ca. 5 m asl) up to 250m asl; in both locality, sampling sites were stratified at 50 m elevational intervals, starting from 5 m (thereafter refer to as 0) and up to 250 m asl (N = 6 sampling sites). At Anse des Papous, a straight line transect was achieved as a function of the distance to the sea. This transect encompassed eight sampling points (0

Fig. 1

 1 Fig.1 Geographical localisation of the three sampling transects at the scale of the Kerguelen archipelago, and localisation of the sampling sites on each transect b) Morphological measurements For each sampling site, 25 individuals were randomly selected (except for specimens sampled at St Malo at 0, 50 and 250 m for which only 12, 21 and 6 beetles were collected, respectively), and further sexed under stereo microscope. Sex ratio was biased toward males in 75% of our samples, and it was necessary to include additional female individuals for Anse des Papous transect (0, 100, 150, 250 and 300 m sampling sites). Pictures of each insect were taken with a video camera (AxioCam ERc 5s, ZEISS, Germany) connected to a stereo microscope. Inter-ocular distance, width and length of the thorax,

  Fig. 2 M. soledadinus N

(

  2013). Analyses were done on pools of three hand-collected carabid beetles (for each insect sampling site, N = 6 replicates for Molloy and St Malo, and N = 5 replicates for Anse des Papous) to depict the metabolic phenotypes of adults from these 17 sampling sites. Dried insect samples were re-dissolved in 600 µL of methanol-chloroform (ratio 2:1, volume:volume) and homogenised using a bead-beating device (Retsch™ MM301, Retsch GbmH, Haan, Germany) at 25Hz for 90s. Four hundred microliters of ultrapure water were added to the samples that were further centrifuged for 10 min at 4000 g at 4° C.Then, 90 µL of the supernatant which contains polar metabolites were transferred to new microtubes, and these aliquots were vacuum-dried(Speed Vac Concentrator, MiVac, Genevac Ltd., Ipswich, England). Dried samples were re-suspended in 30 µL of 20 mg.mL-1 methoxyamine-hydrochloride (CAS Number: 593-56-6, Sigma-Aldrich, St Louis, MO, USA) in pyridine prior to incubation under orbital shaking at 40 °C for 60 min. Following incubation, 30 µL of N-methyl-bis(trifluoroacetamine) (BSTFA, CAS Number: 685-27-8) was added and derivatisation was conducted at 40 °C for 60 min under agitation.

  experimental groups included the parameters distance to the initial sampling point , transect and sex . Graphical results are presented in the figure 3. Males of M. soledadinus are characterised by smaller body sizes than females (χ²=108.25, P < 0.001). The body size is significantly different depending on the transect (χ²=7.76, P= 0.021), with individuals from St Malo being smaller than individuals from Anse des papous (z=-2.75, P=0.016). The distance to the initial sampling point had no significant effect on body size (χ²= 1.72, P = 0.19).

Fig. 3

 3 Fig. 3 Variations in body size index (mean ±SE) measured in male and female M. soledadinus as a function of the distance to the initial sampling point in the three transects (Papou: straight line transect, Molloy and St Malo: altitudinal transects). b) Variations in protein, glycogen and triglyceride contents The model with the lowest AICc value for glycogen concentrations included the parameters transect , distance to the initial sampling point and sex . None of these factors significantly impact the glycogen content in samples (transect: χ²=5.02, P=0.081; sex: χ²=2.77, P=0.096, distance : χ²=3.55, P=0.06), even though individuals sampled farther from the sea show a tendency of increased glycogen content (Fig 4).

  Fig. 4 Variations in glycogen content (in µg.mg -1 of dry mass; mean ±SE) measured in male and female M. soledadinus as a function of the distance to the initial sampling point in the three transects (Papou: straight line transect, Molloy and St Malo: altitudinal transects)

Fig. 5 Fig. 6

 56 Fig. 5 Variations in protein content (in µg.mg - 1 of dry mass; mean ±SE) measured in male and female M. soledadinus as a function of the distance to the initial sampling point in the three transects (Papou: straight line transect, Molloy and St Malo: altitudinal transects)

Fig. 7 Fig. 9

 79 Fig. 7 Variations in triglyceride content (in µg.mg -1 of dry mass; mean ±SE) measured in male and female M. soledadinus as a function of the distance to the initial sampling point in the three transects (Papou: straight line transect, Molloy and St Malo: altitudinal transects) c) Metabolic fingerprintingResults show distinct dynamics of metabolite variation between transects in three out of the five classes of metabolic families (Fig.8). The individuals sampled along the straight line transect show decreasing amounts of FAA (F = 7.16, P =0.0013), IAM (F = 10.59, P <0.001) and Amines (F = 6.46, P =0.0024) with increasing distance to the initial sampling point, when the amounts in these metabolites

  Fig. 10 M. soledadinus a b c

  soledadinus is highly reduced when temperature falls around 4 °C (Lalouette et al. 2012), and thermal conditions are largely suboptimal for adult M. soledadinus when they are dropping to near 0 °C (Lalouette et al. 2012; Laparie & Renault 2016). It is likely that adult M. soledadinus from the two altitudinal gradients experience temperature-imposed resource and physiological limitations when altitude increases.

  significant consequences on the phenotypic traits of the adult, by modifying development duration, in turn affecting body size and fitness of adult(Tigreros, 2013). Several proteins of larval origin are indeed catabolized by female for egg production(Wheeler et al., 2000; O Brien et al., 2002), but additional latent effects of nutritional limitation can be expected (Tigreros 2013). Yet, even though nutrient limitation appears from our dataset from specimens collected along altitudinal transects, it remains uncertain if this nutrient limitation arose from the reduction of the availability of trophic resources or a byproduct of the progressive temperature decrease along the gradient, progressively affecting metabolic activities. Metabolic phenotypes measured in specimens from the straight line transect (Anse des Papous) highly discriminated the samples collected at 0 and 100 m (which grouped with 200 m) on the one hand, and those sampled 400 m far from the seashore on the other hand. The insects from the seashore (0 m) exhibited high concentrations of inositol and pipecolate. At this sampling site, carabid Chapter 5

First, 31

 31 individuals from Patagonia (N =12), South Georgia (N =9) and Kerguelen Islands (Port Couvreux, N =10) were included into two RADseq libraries designed to reconstruct biogeographical relationships between native specimens from Patagonia and those from the introduced populations of subantarctic archipelagos (Kerguelen Islands and South Georgia). As expected, introduced specimens showed decreased levels of genetic diversity compared with individuals from the native area (Patagonia). Interestingly, a higher level of genetic diversity was observed in adult M. soledadinus from South Georgia than from the Kerguelen Islands. This finding suggests that multiple introductions may have occurred in South Georgia (closer to the Falkland Islands, sheep transportations probably occurred between these two archipelagos). Thus, admixture may have contributed to this increased level of genetic diversity. Sequenced imagoes from Port Couvreux (Kerguelen Islands) were characterized by drastic reductions in genetic diversity compared with the other two locations, supporting the single introduction event of this insect at the Kerguelen Islands.Second, five RADseq libraries including individuals sampled from 10 populations of the main island of the Kerguelen archipelago, and distributed along the invasion gradient, were built. The maximum heterozygosity was found in specimens from Port Couvreux, which, again, supports the hypothesis of a unique historical introduction site. The most recent established population, sampled at Val Studer, is the only population presenting a positive FIS (0.004), and for which the Hardy-Weinberg exact test is significant (P =0.008), showing a deficit in heterozygotes. Our results highlight the absence of genetic structure among the ten sequenced populations, even though heterozygosity values show a decreasing pattern from oldest to youngest populations. This later result supports the long-term monitoring data of the range expansion of this species, i.e. colonisation of the mainland was achieved via natural dispersal events from the initial introduction site. Conversely, individuals from the population of Estacade display very homogenous patterns of diversity, which could be explained by human-assisted introduction of few founder individuals from the research station. To complete this study, we need to include individuals from the research station to explore the eventual anthropogenic influence on the current distribution of M. soledadinus, and individuals from the Falkland Islands to finalise biogeographical reconstruction of this species.Chapter 3 -Evidences for phenotypic differentiation between front and core populations suggest spatial sorting dynamicsLaparie et al. (2010Laparie et al. ( , 2013) ) reported a gradual increase of body size in adult M. soledadinus sampled from populations with different their residence times along the invasion gradient. In the second chapter of this dissertation, we prolonged the work of Laparie et al. by analysing the phenotypic change of adult M. soledadinus along the invasion gradient using a vast set of morphological, behavioural and physiological traits (Chapter 3). Individuals were sampled from eight populations of the main island of the Kerguelen archipelago, with residence times ranging from 103 to 4 years since the initial establishment. We first confirmed the morphological gradient previously highlighted byLaparie et al. (2013). We then found that individuals sampled from recently settled populations can support longer periods of starvation and exhibit higher locomotor activity than their counterparts sampled from formerly established populations. These findings support the idea of higher dispersal capacities in specimens at the invasion front. Yet, activities of enzymes involved in energetic metabolism are similar among individuals from these different populations, except for PGI.Activity of this later enzyme was increased in individuals from the older population, which contrasts with most of the available literature. Using GC-TOF-MS metabolomics, a clear cut-off appears in the metabolic phenotypes of specimens sampled from older and younger populations, in both sexes. These promising preliminary results require more in-depth analyses of the potential different metabolic pathways favoured in front populations versus formerly established populations. No differences were found in the propensity to leave a patch, although more precise inquiries of dispersal behaviour are required. This study, by combining phenotypic characterisation of several traits, provides an integrated approach of the phenotypic changes that occur during the range expansion of this species, and suggest the involvement of spatial sorting in this phenotypic differentiation. Chapter 4 -Relative humidity and water accessibility have a prominent role in driving invasion path and settlement of M. soledadinus populations A field-based assessment of the habitat distribution of the invasive carabid beetle M.

Chapter 5 -

 5 Altitudinal habitats are physiologically constraining for M. soledadinus, but still undergo colonisation Altitudinal habitats are being colonised by M. soledadinus since the early 2000 s, possibly driven by ongoing climatic changes. In a fifth step, we investigated the effects of altitudinal gradients on the morphology and physiology of adult M. soledadinus (Chapter 5). Wild imagoes of M. soledadinus were sampled along two altitudinal transects, from sea level to 250 asl, and along a 400mlong straight transect. The straight transect was designed in order to consider the effect of decreasing availability of food resources farther from sea shore from the effects of decreased temperature in altitude. Results show decreased body size in individuals sampled along altitudinal transects. We

3/

  Localities recently colonised at the Kerguelen Islands benefit from precise estimation of the arrival (establishment) of populations of M. soledadinus. At the locality of Isthme Bas, the arrival of M. soledadinus has been anticipated, by setting pitfall traps in four sites in 2005. In two of these locations (IS1 and IS2) M. soledadinus specimens were already present at the start of the experiment. Conversely, in the two other trapping sites (IS3 and IS4) the first individuals arrived sporadically between 2006 and 2010 (see Fig.1). From this dataset, characteristics of the very first colonisers could be explored, including their sex, amounts of body reserve, number of eggs in females, and eventually the age.

Fig. 1

 1 Fig. 1 Number of M. soledadinus caught per year in pitfall traps installed in the locality of Isthme Bas from 2005 to 2015 3 -This invasion case presents several advantages… The invasion process of M. soledadinus at the Kerguelen Islands constitutes a valuable opportunity to study eco-evolutionary processes, and their underlying mechanisms, that occur during range expansion. As outlined in the general introduction of this dissertation, combining the characteristics of the Kerguelen Islands together with those of M. soledadinus makes this model system unique as compared with the majority of invasion cases. The likely unique introduction of M. soledadinus at the

  and larvae.Kubisch et al. (2013) highlighted that kin competition can represent a strong force triggering the initiation of dispersal in invasive species. This should be even truer in environments the native area of this insect species. These replicated invasion situations could allow Saint Paul and Amsterdam islands is really high, especially because the logistic ship Marion Dufresne

  : ces résultats sur l écologie de M. soledadinus aux Iles Kerguelen permettent de mieux appréhender les traits d histoires de vie de cet insecte invasif. Même si le cycle de vie complet reste inconnu, les densités rencontrées sur le terrain suggèrent un fort impact sur les communautés d arthropodes de ce vorace préateur. Chapitre 2les analyses génomiques révèlent la faible diversité génétique et l'absence de structure des populations de M. soledadinus aux Iles Kerguelen Hypothèse 1 : l introduction unique d individus fondateurs a probablement engendré un fort goulot d étranglement et une diversité génétique amoindrie chez les populations de M. soledadinus des Iles Kerguelen comparé aux populations natives. Hypothèse 2 : l expansion géographique naturelle, à partir de Port Couvreux, a probablement entrainé un tri spatial des individus, ce qui pourrait être détecté par un décroissance des niveaux de diversité génétique à partir du site d introduction vers le front d invasion. Méthodologie : une approche moléculaire de RAD sequencing a été testée et s est révélée efficace sur notre modèle biologique. Cette technique consiste à séquencer un sous-échantillonnage du génome correspondant aux régions flanquantes (300 paires de bases) de sites de restrictions spécifiques. Ces sites de restrictions sont distribués le long du génome, et le génotypage de sites polymorphes dans ces séquences permet d estimer la diversité génétique des individus séquencés. Deux jeux de données ont été créés : un premier jeu de données regroupe des individus originaires de Patagonie, de Géorgie du Sud et de Port Couvreux (Kerguelen), et permet de reconstruire une partie de la biogéographie de cette espèce, et de comparer les diversités génétiques des populations natives et introduites. Le second jeu de données regroupe des individus échantillonnés dans 10 populations le long du gradient d invasion de M. soledadinus sur l île principale des Kerguelen, dans le but d étudier la génétique des populations à Kerguelen. Résultats : la diversité génétique des individus de Kerguelen est réduite par rapport aux populations de Géorgie du Sud et de Patagonie, confortant l hypothèse d un unique évènement d introduction. Les analyses de structure montrent que les individus de Géorgie du Sud et de Kerguelen sont plus proches entre eux comparé aux individus de Patagonie. Nous n avons pas trouvé de structure de population le long du gradient d invasion à Kerguelen. La population la plus récente échantillonnée montre un déficit en hétérozygotes, et la population d Estacade, particulièrement homogène est probablement le résultat d une introduction d origine anthropique. Conclusion/perspectives : Afin de finaliser cette étude et de pouvoir valoriser ces résultats, des individus complémentaires doivent être séquencés : des individus des Falkland pour compléter la biogéographie de l espèce, et des individus de la station de recherche de Port aux Français à Kerguelen afin de vérifier l existence d introductions assistées par l homme, depuis la base. Chapitre 3la divergence phénotypique entre les populations anciennement et récemment établies suggère une dynamique de tri spatial Objectifs : cette étude vise à poursuivre la mise en évidence du gradient morphologique établis au cours de l expansion géographique, par la caractérisation de nombreux traits (morphologiques, physiologiques, comportementaux) liés à la dispersion. Méthodologie : des individus ont été échantillonnés dans 8 sites caractérisés par différents temps de résidence le long du gradient d invasion. Ils ont été phénotypés pour les traits suivants : morphologie, capacités de tolérance de jeûne, activité locomotrice, propension à disperser, activités enzymatiques impliquées dans les voies du métabolisme énergétique et quantification en composés circulants (GC-TOF-MS). Résultats : confirmant les études précédentes, les individus échantillonnés dans des populations du front d invasion sont plus gros. Ils sont également plus actifs, résistent mieux au jeûne et présentent des empreintes métaboliques distincts des individus échantillonnés dans des populations plus anciennes. Les activités enzymatiques sont relativement similaires entre toutes les populations et la propension à disperser ne montre pas de différences selon le temps de résidence des populations. Conclusion: Cette étude, par une approche intégrative de traits phénotypiques, permet de démonter l évidence d une différentiation phénotypique au cours de l invasion, entre les populations du front et les populations anciennement établies, suggérant l implication de tri spatial. Chapitre 4 -l'humidité relative et l'accessibilité de ressources en eau déterminent l'établissement des populations de M. soledadinus. Contexte : M. soledadinus est distribué aux Iles Kerguelen le long des côtes et des cours d eau, et on peut se demander quels facteurs environnementaux gouvernent les exigences écologiques relatives à l habitat, entre la disponibilité en eau et en ressources trophiques. Méthodologie : des individus ont été exposés à trois conditions d humidité relative (30%, 70% et 100%), leur survie a été mesurée ainsi que la dynamique de perte d eau corporelle et les modifications métaboliques dans ces trois conditions. En parallèle, des individus ont été isolés et privés de nourriture. Résultats : M. soledadinus est très tolérant à de longues périodes de jeûne, mais survivent comparativement très peu de temps lorsqu ils sont exposés à des conditions moyennes et fortes de stress hydrique. La quantité d eau corporelle décroit rapidement dans ces conditions, et les analyses métaboliques révèlent le déclin rapide de la physiologie des insectes. Conclusions/perspectives : les résultats indiquent que la distribution géographique des populations de M. soledadinus aux Iles Kerguelen est principalement contrainte par la disponibilité en eau. Chapitre 5 -les habitats d'altitude sont contraignants pour M. soledadinus, mais sont tout de même colonisés Contexte : depuis les années 2000 l expansion géographique de M. soledadinus aux Iles Kerguelen comprend la colonisation d habitats en altitude (jusqu à 400m), probablement assisté par le changement climatique. Cette étude s intéresse aux effets morphologiques et physiologiques de la vie en altitude. Méthodologie : des individus ont été échantillonnés le long de deux transects altitudinaux (0 à 250m) et le long d un transect plat, ce dernier servant à discriminer les effets de la diminution en température des effets de la raréfaction de ressources trophiques associées à l éloignement à la côte. La morphologie et la physiologie (composés de réserve, métabolites circulants) de ces individus ont été analysées. Résultats : les individus échantillonnés le long des transects altitudinaux montrent une décroissance de la taille corporelle, qui peut être attribuée aux conditions thermiques suboptimales en altitude lors du développement larvaire. La quantité de glycogène est constante le long des trois transects, les femelles échantillonnées loin de la côte ont des quantités amoindries en protéines et la quantité de triglycérides tend à augmenter chez les individus prélevés en altitude. Les analyses métaboliques permettent de discriminer les échantillons prélevés au bord de la mer (effets de l environnement marin) des échantillons prélevés en altitude, au-dessus de 200m. Ces derniers montrent des patrons métaboliques semblables à ceux d insectes exposés au froid. Conclusion : les conditions thermiques des habitats d altitude sont contraignantes, mais le changement climatique semble permettre la colonisation de ces habitats. Discussion générale 1) Les avantages de ce modèle biologique L invasion des îles Kerguelen par le carabe M. soledadinus constitue une opportunité pour étudier les processus éco-évolutifs et les mécanismes sous-jacents durant l expansion géographique. En effet, ce cas présente une combinaison rare des caractéristiques telles que l introduction probablement unique, à partir d une origine conne, dans un site unique (Port Couvreux). Les résultats des analyses génétiques présentées dans le chapitre 2 corroborent l hypothèse de l évènement unique d introduction, et confirment la chronoséquence de l expansion géographique issue du suivi à long terme de la biodiversité terrestre. Les résultats accumulés sur l écologie de cet insecte invasif représentent des connaissances essentielles pour comprendre la dynamique des populations, les routes potentielles d invasion et délimiter la niche écologique de cette espèce. Ces données pourraient notamment permettre de paramétrer un modèle d expansion afin de prédire la colonisation de l archipel par cette espèce et proposer des mesures de gestion. En combinant les données de distribution, écologiques et génétiques, il serait possible dans un futur proche de construire une matrice de résistance qui mettrait en évidence les habitats les plus favorables et les chemins de moindre coûts entre eux à l échelle des îles Kerguelen. Un modèle préliminaire inclurai la topographie, parce que M. soledadinus est trouvé jusqu à 400m d altitude, et que les habitats d altitude sont contraignants (chapitre 5). De plus, la distribution littoral et le long de cours d eau, ainsi que la faible tolérance à la dessiccation indiquent un fort coût des habitats éloignés de la côte et du réseau hydrographique. Aux îles Kerguelen, M. soledadinus n a pas de compétiteur. En revanche, de forts taux de compétition intra-spécifiques sont attendus dans les localités à fortes densités. Des interactions cannibales ont été observées en conditions contrôlées entre adultes et entre adultes et larves. En théorie, la compétition de parentèle est une force majeure pouvant déclencher la dispersion chez certaines espèces. Les analyses du chapitre 2 n ont pas permis de mettre en évidence de structure génétique le long du gradient d invasion, ce qui pourrait être expliqué par un faible nombre d individus fondateurs (en 1913). Si cette hypothèse est vraie on peut d attendre à de forts degrés de parentés entre les individus, et à une augmentation de ce degré de parenté dans les populations du front d invasion, en raison des différents évènements fondateurs depuis le site de Port Couvreux. Des reconstructions de parentèle sont donc requises afin de valider ou d infirmer cette hypothèse. Merizodus soledadinus a été accidentellement introduits aux îles Kerguelen mais aussi en Géorgie du Sud. Ces deux îles subantarctiques partagent des conditions climatiques similaires avec l aire native de cet insecte (pré-adaptation). Ces cas « répliquées « d invasions constituent un terrain fertile pour la mise en place d études comparatives des patrons écologiques et évolutifs impliqués dans l introduction et l expansion géographique. Cette situation permettrait notamment de tester la prédiction théorique selon laquelle la dynamique d expansion est réduite si l espèce focale est en compétition avec une ou plusieurs autres espèces. Or, en Géorgie du Sud, M. soledadinus est en compétition avec le carabe Trechisibus antarcticus. Des études de l écologie de ces deux milieux permettraient de comparer et de quantifier les effets de la compétition intra et inter-spécifiques sur la dynamique de l expansion géographique. 2) Les limites du modèle biologique 1/ Où sont les larves ? Des lacunes importantes restent à combler dans la compréhension de la biologie de la reproduction et le cycle de vie de cet insecte, et particulièrement des stades larvaires : les besoins trophiques et abiotiques, les taux de recrutement, les pressions de prédation/compétition, les capacités de mouvement. La compréhension du cycle de reproduction constitue cependant un verrou essentiel pour appréhender la dynamique des populations. De plus, le control de la reproduction via l élevage permettrait d étudier l héritabilité des caractères, en particulier ceux pour lesquels des variations ont été mises en évidence (chapitre 3) entre les populations du front d invasion et les populations anciennement établies. 2/ Déterminer l âge Les résultats des différentes expériences sont soumis à la variabilité inter-individuelle du sexe, du statut trophique et de l âge des individus échantillonnés. Les protocoles expérimentaux ont été conçus pour atténuer ou prendre en compte ces biais, excepté pour l âge, qui demeure incertain. L âge des individus pourrait être estimé en formant des classes d âge à partir d indices morphologiques tels que l usure mandibulaire ou des tarses, ou via la quantification d hydrocarbones cuticulaires qui varient selon l âge. 3/ Régime trophique Le régime trophique de M. soledadinus a été évalué par des expériences de choix de proies potentielles en conditions contrôlées. Une analyse précise du régime requière des analyses de metabarcoding du contenu du tractus digestif. Les résultats du chapitre 3 montrent une augmentation de la résistance au stress trophique et de l activité locomotrice des individus du front d invasion. Combinés à l activité annuelle continue de cet insecte, ces résultats suggèrent la poursuite de la colonisation de sites de plus en plus éloignés. Il est possible que le comportement de nutrition change selon le temps de résidence des populations, avec des besoins énergétiques plus forts des populations au front d invasion comparé aux populations intermédiaires et anciennement établies, en fonction de la disponibilité en nourriture et de l abondance en proies et prédateurs. Pour répondre à cette question, une expérience de comparaison de la réponse fonctionnelle d individus issus de 6 populations le long du gradient d invasion a été réalisée (résultats en cours d analyse, non présentés ici). 3) Expériences menées pendant la thèse mais non inclues dans le manuscrit de thèse 1/ Reconstruction de parenté Cette expérience vise à étudier la structure de parenté à fine échelle géographique, afin de mieux comprendre la dynamique locale de dispersion. Ainsi, 639 adultes ont été échantillonnés le long d un transect de 1500m parallèle à la côte à Cataractes, et ont été génotypés à 13 loci microsatellites. Les relations de parentés seront extraites à l aide du logiciel Coancestry. 2/ Réponse aux stress La théorie prédit qu au cours de l expansion géographiques, les individus du front d invasion auront des réponses au stress différentes des populations plus anciennement établies en raison de leur plus fréquente exposition à des conditions environnementales nouvelles. Ainsi, des individus échantillonnés dans 6 populations de long du gradient d invasion ont été exposés à des conditions stressantes : dessiccation, jeûne, régime thermique fluctuant chaud et les trois stress en même temps. Cette expérience est toujours en cours à Port-aux-Français. 3/ Colonisation à Isthme Bas Les sites les plus récemment colonisés bénéficient d une estimation précise de la date d arrivée et de l établissement de M. soledadinus. A Isthme Bas, cette arrivée a même été anticipée avec la pose de pièges barber en 2005, et l arrivée sporadique des premiers individus entre 2006 et 2010. A partir de ces échantillons, il sera possible de caractériser les premiers colonisateurs au front d invasion (sexe, quantité de réserves corporelles, charge en oeufs des femelles, âge éventuellement). Pour conclure, les données collectées sur l écologie de M. soledadinus à Kerguelen suggèrent que la colonisation va se poursuivre. Les procédures de bio-contrôle (champignons entomopathogenes) sont inenvisageables, et la prévention reste le meilleur moyen de gérer cette invasion. Les mesures de biosécurité instaurées en 2013 sont probablement efficaces pour éviter le transport assisté par l homme au sein de l archipel, mais aussi de Kerguelen vers Amsterdam et St Paul, où le Marion Dufresne passe juste après Kerguelen au cours de sa rotation.

  Keywords: Biological Invasions, Dispersal Ecology, Ecophysiology, Phenomics, Population Genetics RÉSUMÉ Le commerce mondial et les mouvements humains accroissent les probabilités de transport à longue distance de propagules, et leur introduction dans de nouvelles aires géographiques. Dans certains cas, des espèces récemment établies peuvent devenir dominantes dans la communauté envahie. Malgré les menaces sur les communautés natives et le fonctionnement des écosystèmes, les invasions biologiques constituent des expériences naturelles qui permettent d étudier les processus éco-évolutifs en temps réel, notamment l impact de nouvelles interactions biotiques sur la composition et la dynamique des communautés, l adaptation rapide à de nouvelles conditions environnementales, ou la dispersion en limite de répartition. Les îles océaniques sont particulièrement sensibles aux invasions biologiques en raison de la faible diversité de leurs communautés natives. Dans les terres australes françaises, le carabique marcheur Merizodus soledadinus, natif de Patagonie, a été accidentellement introduit à Kerguelen en 1913. La présente étude vise à comprendre les principaux mécanismes à l origine du succès invasif de cet insecte aux Iles Kerguelen. Un large ensemble de méthodes ont été utilisées pour explorer les traits écologiques de M. soledadinus, des populations à la molécule. Les analyses génétiques confortent l hypothèse historique d un unique évènement d introduction dans un seul site des Iles Kerguelen. Les populations échantillonnées le long du gradient d invasion ne montrent pas de structuration génétique. Les traits phénotypiques mesurés montrent une forte différentiation entre les individus selon le temps de résidence des populations, confirmant l hypothèse de tri spatial des populations au cours de l expansion géographique. Nous avons démontré que l expansion géographique et la sélection d habitats par M. soledadinus est principalement gouvernée par la disponibilité en eau, comme le suggère par la forte sensibilité des adultes au stress hydrique. En parallèle, la colonisation d habitats en altitude dépend des conditions thermiques, qui semblent être contraignantes pour cet insecte à partir de 200m d altitude. La colonisation d habitats d altitude progresse pourtant, probablement assistée par le changement climatique. Pour finir, les adultes M. soledadinus sont longévifs et actifs toute l année. Les connaissances apportées sur l écologie de M. soledadinus et sur la dynamique de son expansion géographique suggèrent la poursuite de la colonisation de l archipel par ce prédateur. L ensemble de ces connaissances pourraient être utiles à la paramétrisation d un modèle d expansion géographique, qui permettrait de définir les routes de dispersion et les taux d expansion, dans l objectif d assister les mesures de gestion par les agents de la Réserve naturelle des Terres Australes et Antarctiques Françaises. Mots-clefs : Ecologie de la Dispersion, Ecophysiologie, Génétique des Populations, Invasions Biologiques Phénomique

  Chapter 3 isomerase (PGI) activities were measured on whole body extracts of M. soledadinus. Citrate synthase (CS), malate dehydrogenase (MDH) and fumarase activities were measured on mitochondrial extracts from adult M. soledadinus. These assays were restricted to specimens from four populations, i.e. Port Elizabeth and Cataractes (formerly colonised habitats) on the one hand, and Isthme Bas and Val Studer (recently colonised habitats) on the other hand. Specimens from Pointe Suzanne were also added in the total antioxidant and HK assays. Three sets of 24 ground beetles (12 males and 12 females) were isolated by sex and last fed at least four days prior to extractions: one set for the antioxidant assay, one set for both HK and PGI, and finally one set for the mitochondrial extraction and the following enzyme quantifications. For each set, 12 samples constituted by two alive beetles of the same sex were weighted and maintained on ice just before extraction.

 Total antioxidant activity, phosphoglucoisomerase and hexokinase Quantifications of total antioxidant activity, PGI and HK were performed following manufacturer s instructions (Cayman assay kit number 709001, and Sigma assay kits MAK103 and MAK091, respectively). Whole body samples were extracted in 300µL of extraction buffer supplied with the kits, using a bead-beating device (Retsch™ MM301, Retsch GbmH, Haan, Germany) and homogenised for 1.5min at 25Hz. Samples were then centrifuged (10 min, 1 500g, 4 °C).

  Three citrate synthase samples (two from Isthme Bas, one from Val Studer) and one fumarase sample (from Cataractes) were removed due to debris causing abnormal absorbance curves. The final enzyme activity was corrected by the protein concentration of each sample. Proteins were quantified from five µL of mitochondrial extract reacting with 245µL of Bradford (absorbance red at 595nm), and the protein amounts were calculated from a BSA standard curve.

g) Metabolic phenotyping

Concentrations of metabolites (amino acids, hydroxyl acids, carbohydrates, sugar acids, sterols, aromatics, nucleosides, and amines) were measured from whole body extracts using Gas chromatography -Time of Flight -Mass Spectrometer (GCTOF-MS). From the 75 individuals sampled at the localities of Port Couvreux, Val Travers and Cataractes (formerly colonised habitats), and Pointe Suzanne, Isthme Bas and Val Studer (recently colonised habitats), six males and six females were isolated and vacuum-dried for 15 hours (Speed Vac Concentrator, MiVac, Genevac Ltd., Ipswich, England) before being weighted (Balance XP2U Mettler Toledo, Columbus, OH, d=0.1 µg). The samples were sent to the West Coast Metabolomics Center (University of California, Davis) for whole body extraction and GCTOF-MS procedure, as detailed in Fiehn et al. (2008). Briefly, the samples were extracted through bead-beating (Retsch ball mill, Retsch GbmH, Haan, Germany) for 30s at 25Hz.

  of five enzymes of major importance in glycolysis and Krebs cycle were comparable. Sex was also an important factor explaining differences between individuals.The morphometric analysis confirms the morphological gradient described earlier by Laparie et al.(2010, 2013). As our measurements were performed on different populations (except Port Couvreux and Port Elizabeth that are included in these three studies) sampled at different time points, this finding gives a high level of confidence to this body size gradient. Individuals from the invasion front are significantly larger than individuals from formerly established (core) populations. This larger size is predominantly explained by increased size of different tagma depending on sex: females have larger pronotum size and males have larger abdomen size. Variations in the accessibility to trophic resources among localities may contribute to this body size pattern.Lebouvier et al. (2011) pointed out the existence of a negative correlation between the abundances of native species and M. soledadinus

	Chapter 3
		Metabolic fingerprinting
							P
							P
				P			P
	Fig. 11						M. soledadinus
							N
	. 10						M.
	soledadinus
	4 -Antioxidant	Residence Time χ² P Discussion 0.0001 0.99	χ² 21.1	Sex <0.001 P	Tab. 2	M. soledadinus
	HK		0.0003	0.98	7.52	<0.01
	PGI		7.52	<0.01	1.42	0.24
	Citrate Synthase	0.03	0.97	2.26	0.14
	Fumarase		1.09	0.3	1.15	0.7
	Malate DH		1.84	0.18	2.02	0.16

in formerly colonised localities. The predation pressure of M. soledadinus larvae and adults on potential preys could impose shifts towards preying on invertebrates of suboptimal quality in core populations. Conversely, at the invasion front, colonists would benefit from a larger -potentially unlimited -pool of preferred preys, authorizing the production of offspring of larger sizes. However, this hypothesis cannot solely explain this body size pattern, which has also been demonstrated in insects from other taxa

(Hill et al., 1999; Abril et al., 2013)

. In our model system, individuals of M. soledadinus from Cataractes (36 years of residence time) are among the smallest measured insects. At this locality, prey diversity and density are still relatively important. For instance, there are large populations of native diptera (pers. obs.), which are profitable for M. soledadinus

[START_REF] Colinet | Exploring the plastic response to cold acclimation through metabolomics: metabolomics of cold acclimation response[END_REF]

. Conversely, the individuals from Val Studer (range edge population, 4 years of residence time) have large body size despite low estimated prey availability/diversity in this inland valley. Altogether, these observations suggest that there may be other important factors triggering this morphological gradient, of which spatial sorting at the expanding range of M. soledadinus could be proposed.

  Numerical outputs of the post-hoc test of the MANOVA performed on the 42 quantified metabolites. The multivariate linear regression included distance to the initial sampling point and transect as explanatory variables. The factorial reference for transect was Anse des Papous, the straight line transect. The extent of variation in metabolites compounds from this reference are respectively expressed in the two columns Molloy and St Malo . Significance levels: P<0.05 *; P< 0.01 **; P< 0.001 *** These datasets constitute the first available genetic information on this ground beetle. A first try-out was performed by constructing a RADseq library including 16 individuals from the Kerguelen Islands. The success of this first library led to the building of two distinct datasets.

	Chapter 5
	Sampling Site MR 0 MR 50 assumptions, molecular approaches (Restriction Site Associated DNA, RADseq) were undertaken Latitude Longitude Altitude (m) Distance from origin point (m) -49.345091 70.170657 0 0 -49.344643 70.170674 0 t-value P t-value P t-value P 50 Molloy St Malo Distance Tab. S2 ref= Papous (Chapter 2).
	MR 100 MR 150 MR 200 Arabinose Adonitol Alanine Papous MR 250 Arabitol Asparagine	-49.344125 -49.343732 -1.347 -0.743 -49.343355 -1.286 -49.342906 -1.047 -2.878 0.005031 ** 70.170649 70.170666 0.182 0.46 70.170777 0.20191 70.171034 0.298019	-1.569 -1.526 -2.913 -1.468 -3.543	0 0 0 0 0.000638 *** 0.12 0.131 0.00455 ** 0.145749	0.203 0.587 1.659 -0.712 0.127	0.839 0.559 0.1008 0.478083 0.899431
	MR 300 Aspartate	-49.342513 -2.294	70.171451 0.02419 *	-3.026	0	0.00326 **	0.036	0.97134
	MR 400 RJ 0 Citrulline Citrate Erythritol	-49.341733 -2.545 -49.340408 -2.476 1.867	70.172401 0.012698 * 69.82201 0.01522 * 0.0652 .	-2.392 -3.24 -0.243	0 0	0.018896 * 0.00169 ** 0.8082	3.524 0.617 -0.167	0	0.000679 *** 0.53883 0.8679
	RJ 50 Ethanolamine Molloy RJ 100 Fructose RJ 150 Fumarate RJ 200 GABA Galactitol	-49.336666 -2.083 -49.33484 1.989 -49.334229 -3.176 0.002069 ** 69.820862 0.04019 * 69.81988 0.0498 * 69.821391 -49.332949 69.823367 -1.484 0.1413 -0.07 0.944	-2.973 1.402 -3.478 -3.142 -1.956	50 100 0.00382 ** 0.1644 0.000791 *** 150 200 0.0023 ** 0.0536 .	0.514 0.214 3.198 0.776 1182 0.96	0.60876 0.8307 0.001931 ** 0.44 0.3399
	Galactose	RJ 250	-49.331579 1.284	69.823382 0.202	-0.141	250	0.888	1242 -0.155	0.877
	St Galacturonate KO 0 KO 50 Gluconolactone KO 100 Glucose Glutamate Malo KO 150 Glycerate KO 200 Glycerol3P Glycine	-49.361968 -0.899 -49.357872 -0.22 -49.357642 1.275 -2.9 0.004721 ** 70.06634 0.371 70.062506 0.826 70.059627 0.2056 -49.358327 70.054793 -1.438 0.1541 -49.359952 70.050551 -0.7 0.48527 -0.94 0.3518	-0.792 -1.588 1.683 -3.711 -1.853 -2.693 -2.591	0 50 100 0.000364 *** 0.4304 0.116 0.0959 . 0.0673 . 150 0.00849 ** 200 0.0112 *	2.068 1.243 0.893 0.766 1.359 0.971 1.448	0	0.0416 * 0.217 0.3743 0.445853 0.1778 0.33444 0.1511
	Inositol	KO 250	-49.361342 1.306	70.049556 0.195	-0.304	250	0.762	1018 0.662	0.509
	Isoleucine	-2.26		0.02634 *	-3.122		0.00244 **	0.558	0.57839
	Lactate			1.61		0.111	0.38			0.705	1.483	0.142
	Leucine			-2.66	0.009376 **	-3.48	0.000781 ***	0.12	0.905035
	Lysine			-2.648		0.00960 **	-3.194		0.00196 **	0.397	0.69249
	Malate			-0.656		0.513	-0.913			0.364	1.036	0.303
	Mannitol			0.577		0.5656	1.34			0.1837	1.014	0.3135
	Mannose			-0.563		0.575	-1.633			0.106	1.12	0.266
	Methionine	-2.902	0.004690 **	-3.758	0.000309 ***	0.566	0.572828
	Phenylalanine	-2.445		0.01652 *	-3.245		0.00167 **	0.323	0.74753
	Phosphorate	-2.191		0.03115 *	-3.105		0.00257 **	1.365	0.17592
	Pipecolate	-3.328	0.001282 **	-3.717	0.000356 ***	2.252	0.026827 *
	Proline			-1.966		0.0525 .	-1.006			0.317	1.847	0.0682 .
	Putrescine	-2.317		0.02286 *	-2.723		0.00781 **	0.614	0.54065
	Serine			-2.719		0.00790 **	-2.973		0.00381 **	-0.01	0.99204
	Sorbitol			0.792		0.43055	-0.745			0.45816	1.254	0.21329
	Succinate		0.751		0.455	0.081			0.936	0.346	0.73
	Threonine	-2.559		0.01223 *	-3.17		0.00211 **	0.269	0.78844
	Tryptophane	0.911		0.365	-0.382			0.703	0.702	0.484
	Valine			-2.228		0.02843 *	-3.123		0.00243 **	0.731	0.46653

  Depuis la révolution industrielle et l explosion de la démographie humaine, le transport et l introduction par l homme de propagules hors de leur aire de répartition s est multiplié, entrainant un nombre croissant d exemples de communautés natives dominées par des populations d espèces arrivées récemment. Les invasions biologiques sont désormais comprises dans le top 5 des menaces qui pèsent sur la biodiversité, aux côtés du changement climatique, de la fragmentation des habitats et du changement d usage des sols, et participent à l homogénéisation de la biodiversité. L intérêt des chercheurs pour les invasions biologique fut principalement initié par le lancement du programme SCOPE en 1982. En premier lieu, l étude des espèces invasives est motivée dans un but de conservation (les comprendre pour les gérer), mais d autres domaines de recherche se sont focalisés sur les invasions biologiques parce qu elles constituent des expériences naturelles idéales pour étudier Williamson et Richardson ont travaillé à l élaboration de concepts généraux, sur les invasions d animaux et de plantes respectivement. Leurs travaux ont permis d établir que le processus d invasion est une séquence d étapes ou de barrières auxquels les propagules sont confrontées. Les trois stades principaux sont la phase de transport, pendant laquelle les propagules prélevées dans l aire native doivent survivre au transport vers l aire d introduction, puis la phase d établissement, pendant laquelle les propagules introduites doivent réussir à survivre et se reproduire de manière à installer une population pérenne (ce stade est souvent associé à une période de latence, parce que l établissement d une population viable peut nécessiter de multiples introductions et/ou une période d adaptation aux nouvelles conditions environnementales rencontrées). Enfin, la troisième et dernière phase, l invasion, pendant laquelle la population établie et pérenne va proliférer et étendre son territoire. Cette dernière phase est souvent rapide et exponentielle. La recherche sur les espèces invasives et le processus d invasion s est longtemps penché sur la caractérisation générale de traits partagés par les espèces invasives et/ou par les environnements envahis afin d essayer de prédire l émergence d invasions biologiques. Par exemple, les caractéristiques d un « bon envahisseur » rassemblent des traits d histoire de vie favorisant une La recherche de traits généraux partagés par les espèces invasives et les environnements envahis est souvent peu concluante et faiblement applicable : en effet les travaux qui ont exploré ces hypothèses ont dévoilé la grande variété de stratégies invasives, dépendant à la fois des caractéristiques des espèces et des habitats étudiés. Le succès invasif est aujourd hui vu comme la correspondance entre Le développement récent d outils moléculaires qui permettent le séquençage à haut débit et à prix raisonnable a permis l accès à ces techniques pour des organismes non model, ce qui est souvent le cas pour les populations invasives.Les populations introduites sont le plus souvent fondées par un très petit nombre de propagules, qui portent une fraction réduite de la diversité génétique initiale (population d origine), et sont souvent caractérisées par de forts taux de consanguinités. La diversité génétique constitue le substrat du potentiel adaptatif des espèces, qui permet l adaptation à de nouvelles pressions de sélection. Le adaptation locale et parfois rapide des espèces introduites fait l objet de questionnements au sein de la communauté des biologistes évolutifs, à savoir sur quel substrat de variabilité génétique la sélection naturelle agit-elle dans les cas de faible diversité génétique. La piste de la variation génétique stagnante (« standing genetic variation ») est favorisée au profit de l apparition de nouvelles mutations, parce que ces dernières ont des probabilités plus réduites d être bénéfiques et d atteindre des fréquences suffisantes pour se fixer.Une hypothèse alternative pour expliquer l adaptation locale des espèces introduites dans les cas de faible diversité génétique serait la plasticité phénotypique, qui confèrerait de bonnes performances dans une large gamme de conditions environnementales. Cette plasticité étant couteuse, il est probable qu elle ne soit bénéfique que pendant les premiers stades de l invasion, pour ensuite disparaitre au profit de la fixation d allèles adaptés localement.4) La dispersion au front d'invasionLa phase d expansion géographique caractérise les espèces invasives, qui ne sont parfois détectées qu à ce stade du processus d invasion. Les capacités de dispersion des individus déterminent la vitesse de colonisation de nouveaux habitats. Le processus d expansion combine des évènements de dispersion à petite distance et quelques évènements de dispersion à longue distance, constituant une succession de fondations. Les individus qui dispersent le plus loin ont théoriquement des avantages directs en termes de fitness, en raison des pressions de compétition moindre dans les milieux colonisés par peu d individus contrairement aux populations densément peuplées de la population d origine. Le front d invasion est donc constitué d habitats colonisés en premier lieu par les individus disposant des meilleures capacités de dispersion. En se reproduisant entre eux, au fur et à mesure de l avancée du front il peut se produire un effet de « Village Olympique », où les descendants des populations du front d invasion sont dotés de capacités accrues de dispersion (si les traits de dispersion sont La faune terrestre est dominée par la communauté d arthropodes, la plupart des espèces étant des décomposeurs, concentrés au bord de mer auprès des colonies d oiseaux et de mammifères marins qui viennent muer et se reproduire. Ces colonies constituent la majeure partie des intrants de nutriments dans l écosystème terrestre des îles subantarctiques, expliquant une recherches, peuplées pendant l été austral ou à l année, ont été bâties dans les années 1950. Malgré leur isolement géographique extrême et la courte histoire anthropique, les îles subantarctiques abritent de nombreuses espèces introduites, parfois surpassant les effectifs de diversité spécifiques natives. Les relevés climatiques à long termes (>50 ans) montrent que ces îles sont également soumises à un rapide changement climatique, se traduisant par des hivers moins froids et une diminution des précipitations. Les îles subantarctiques constituent des laboratoires à ciel ouvert, qui permettent d étudier les processus écologiques dans des conditions de faible impact anthropique (excepté pour le changement climatique), au sein de chaines trophiques réduites à faible redondance fonctionnelle. La diversité spécifique réduite ainsi que la surface restreinte de ces îles favorisent le suivi à long terme des populations ainsi que la détection d espèces nouvellement introduites. Outre les avantages indéniables que ces caractéristiques confèrent à la protection et à la conservation de ces milieux, elles permettent également d étudier les mécanismes et la dynamique associés aux invasions biologiques, tels que l expansion géographique, les impacts de nouveaux prédateurs ou compétiteurs sur les communautés natives, les modifications post-introduction. Etant donné la faible étendue des impacts anthropiques sur ces écosystèmes, l impact direct le plus notable de l activité humaine sont les espèces invasives. il ne le trouve qu autour des baraquements abandonnés de la bergerie. Depuis 1939, la distribution de cette espèce sur l archipel est régulièrement suivie, et ces données fournissent des informations précises sur la dynamique d expansion géographique de cette espèce, et notamment sur les temps de résidence des différents sites colonisés le long du gradient d invasion. Des études ont d ailleurs montré une relation négative entre ce temps de résidence et les abondances d espèces de diptères natives, suggérant un fort impact de prédation de M. soledadinus sur les communautés natives d arthropodes. Une étude récente a mis en évidence que les populations récemment établies étaient composées d individus plus gros que les populations anciennement établies, suggérant une possible différentiation phénotypique le long du gradient d invasion entrainée par un tri spatial. Cette thèse a pour but de contribuer à l explication du succès invasif de M. soledadinus aux îles Kerguelen, à travers l utilisation d une combinaison de méthodologies alliant l autécologie classique, la génomique, la métabolomique et le comportement. Chapitre 1 -Les adultes de M. soledadinus vivent longtemps, sont actifs à toutes les saisons et il n'y a pas de période de ponte Contexte : cette étude vise à améliorer nos connaissances sur l autécologie de cet insecte aux Iles

	Résumé en Français
	Caractérisation phénotypique et génétique du carabique invasif
	Merizodus soledadinus aux Iles Kerguelen Etant donné l intensité actuelle du commerce global, le nombre probable d introductions doit être très Les outils moléculaires sont beaucoup utilisés pour reconstruire les routes d invasions (les vecteurs de
	Pour mes parents… élevé. Cependant, peu de propagules introduites conduisent à l établissement d une population viable, transport) et l origine des populations invasives. Ces études, couplées à des données historiques,
	et encore moins deviennent invasives. La force des contraintes imposées par les filtres constituent des outils puissants pour mieux appréhender les origines des populations envahissantes Introduction La distribution des espèces varie naturellement, en raison de modifications climatiques ou environnementaux déterminants le succès des espèces invasives a été illustré par la Règle des 10 de Williamson (1996) : sur 100 espèces introduites, 10 réussiront probablement à établir une population et constituent une base solide pour tester des hypothèses éco-évolutives entre les populations natives et introduites. Kerguelen.
	viable et une seulement risque de devenir invasive. d interactions biotiques. en temps réel les processus éco-évolutifs, comme le changement de niche écologique, les 2) Invasibility et invasiveness
	proliférations, l accélération du front d expansion. Il résulte de cet intérêt un nombre aujourd hui
	pharamineux d études de cas d invasions biologiques, qui sont menées à l aide de méthodes
	différentes, dans des objectifs différents, sur une grande variété de modèles taxonomiques. Ce
	foisonnement a donné lieu à l émergence de concepts et de terminologies parallèles et synonymes
	(non-native, introduite, exotique, établie, invasive…). Des cadres théoriques généraux ont vu le jour
	ces dix dernières années afin de clarifier le débat, et afin de généraliser et unifier les concepts relatifs
	aux invasions biologiques.
	1) Le processus d'invasion
	une population et un système. concentration d espèces près du rivage. Les îles subantarctiques abritent une forte proportion
	3) L'apport des biologistes évolutifs d espèces aptères par rapport à d autres systèmes (insulaires ou continentaux), probablement à cause
	Un peu plus tardivement que les écologues, les évolutionnistes se sont finalement aussi intéressés aux de l environnement à la fois froid et venteux, où la fonction de vol est désavantagée.
	invasions biologiques. En effet, ces expériences naturelles permettent d étudier l adaptation et la Les îles subantarctiques ne sont pas habitées et ont une histoire anthropique récente et tournée vers

reproduction rapide, un large régime trophique, de fortes capacités de compétition. Les environnements sensibles aux invasions biologiques sont souvent caractérisés par des communautés natives peu diversifiées. En effet, dans un environnement insaturé , la probabilité pour une nouvelle espèce d établir une population viable dans une niche écologique sous-occupée est plus forte (si les autres conditions biotiques ou abiotiques le permettent). Dans ce contexte, les écosystèmes insulaires apparaissent particulièrement sensibles aux invasions biologiques, de par le fréquent fort taux d endémicité de leurs communautés indigènes. D autre part, la perturbation des milieux est généralement reconnue comme un facteur facilitant l établissement d espèces non natives, et la question est souvent posée de savoir si les espèces invasives ne seraient que des « passagers » du changement global, des « symptômes » de l affaiblissement des communautés introduites. réponse à de nouvelles pressions de sélections à une échelle temporelle écologique, et non géologique. Malgré l intérêt récent porté sur le sujet par les biologistes de l évolution, des avancées majeures ont été réalisées vers la compréhension des changements évolutifs durant les invasions. paradoxe génétique des invasions pose le problème suivant : comment les espèces invasives s adaptent aux nouvelles conditions rencontrées malgré une diversité génétique réduite ? La comparaison des niveaux de diversité entre populations natives et introduites révèle des résultats contrastés : si de nombreuses études ont démontré des niveaux réduits de diversité génétique dans les populations introduites comparées aux populations natives des mêmes espèces, des niveaux supérieurs de diversité ont également été mis en évidence. Ces patrons sont attribués à des phénomènes d « admixture », de mélange de diversité génétique originaire de différentes populations sources dans le cas d introductions multiples. Les goulots d étranglement génétiques (« bottlenecks ») ne semblent pas contraindre le succès invasif ni même l adaptation rapide des espèces introduites. Des mécanismes moléculaires peuvent assister le potentiel invasif des espèces, comme des inversions chromosomiques (mises en évidences dans le cas de l invasion du continent américain par Drosophila subobscura) ou comme l hybridation intra-ou interspécifique, qui peut entrainer la formation de phénotypes transgressifs (à la fitness meilleure que celles des deux parents, c est par exemple le cas chez les spartines). L héritables). La répétition de ce phénomène entraine, au fil des générations, une différentiation phénotypique entre les populations anciennement établies et le front d expansion. Ce phénomène est appelé le tri spatial. 5) Présentation du système étudié : un carabique aux Iles Kerguelen Les îles subantarctiques sont situées entre 45° et 54° de latitude sud et constituent la majeure partie des écosystèmes terrestres dans cette région du globe. La gouvernance de ces îles se partage entre le Royaume Uni, l Afrique du Sud, la France, l Australie et la Nouvelle Zélande. Ces îles sont de taille variable, quasiment toutes volcaniques, et partagent des similarités en terme de conditions climatiques (forte influence du vent, beaucoup de précipitations, faibles variabilités saisonnières, température annuelle moyenne entre 1.5 et 10°C) et de biotopes (faible diversité d espèces et de groupes fonctionnels, absence d arbres). la mer (découvertes fin du XVIème siècle, longue période baleinière à partir du milieu du XIXème). Certaines îles sont très rarement visitées, principalement par des scientifiques, et demeurent des sanctuaires (comme par exemple l île aux Cochons de l archipel de Crozet) ; sur d autres îles des stations de Les politiques de conservation ont entrainé la mise en place de tests d éradication sur différentes îles et ilots, ce qui permet d étudier à long terme les processus de recolonisation et les mécanismes de résilience dans ce contexte subantarctique. Les îles subantarctiques sont des sites majeurs de l étude aujourd hui cruciale des effets combinés des invasions biologiques et du changement climatique. Merizodus soledadinus est un carabique prédateur natif de la Patagonie et des îles Falklands. Il a été observé pour la première fois en Géorgie du Sud en 1982, et à Kerguelen en 1939. Les données historiques suggèrent que l introduction de cette espèce à Kerguelen résulte d un unique évènement, lorsque les frères Bossières expérimentèrent un élevage de moutons, notamment originaires des Falkland, sur le site de Port Couvreux. Lorsque René Jeannel observe Merizodus soledadinus en 1939,

Val Travers (51) X X Port Elizabeth (46) X X X Cataractes (36) X X X X X X Anse des Pachas (21) X X Pointe Suzanne (10) X X X X X Isthme Bas (6) X X X X X X Val Studer (4) X X X X X

Acknowledgments

The French Polar Institute Paul-Emile Victor that supports our program IPEV 136 Subanteco is warmly thanked. This study was granted by InEE-CNRS (Enviromics call, ALIENS ; Zone Atelier Antarctique et Subantarctique). Part of the experiments were conducted at the ABGC platform (UMR CNRS EcoBio). Our samplers and breeders of Merizodus soledadinus at Port-aux-Français from 2013 to Acknowledgments Carl Vangestel and Katrien de Wolf are warmly thanked for their help and advises during data processing and analyse. Mathieu L., Christophe D. and Bernard K. are also thanked, for their help during fieldwork. This study benefited from a InEE-CNRS grant (Enviromics ALIENS ), and was supported by the Synthesys program, by the French Polar Institute (IPEV, program 136) and by CNRS (Zone Atelier Antarctique et Subantarctique) Acknowledgments Camille Leclerc, Marc-Antoine Colleu, Hoël Hotte and MSc trainee François le Cor are warmly thanked for their contribution in producing these datasets. Maxime Dahirel provided significant improvement to the statistical analyses and is therefore thanked***. This research benefited from the InEE-CNRS grant (Enviromics call ALIENS ), and was supported by the French polar Institute (program IPEV 136) and by Centre National de la Recherche Scientifique (Zone Atelier Antarctique et Subantarctique). Part of the experiments were conducted at the PLAY platform (UMR CNRS Ecobio). Acknowledgments We thank the French Polar Institute Paul-Emile Victor that supports our program IPEV 136 SUBANTECO , and all people from IPEV who are of great help in assisting us with the field logistics in Îles Kerguelen archipelago. This study was granted by InEE-CNRS (Enviromics call, ALIENS ; Zone Atelier Antarctique et Subantarctique). Part of the experiments were conducted at the ABGC platform (UMR CNRS EcoBio). Solène Lebreton and Camille Thomas, the nurses of Merizodus soledadinus at Acknowledgments We are very grateful to Maxime Dahirel for his statistical support and advices, and to the helpful IPEV logistics team that greatly facilitates field work. This research was granted by InEE-CNRS (Enviromics call, ALIENS ; Zone Atelier Antarctique et Subantarctique), and supported by the French Polar Institute (IPEV, program 136) and the CNRS (Zone Atelier de Recherches sur l Environement Antarctique et Subantarctique). Metabolic analyses were performed on the PLAY platform (UMR CNRS Ecobio, Rennes, France).

s pour la science pendant cet t e t hèse.

« L'Homme est fils de la forêt et père du désert »

: Taxonomy and distribution

Merizodus soledadinus

Merizodus soledadinus

Oopterus soledadinus, which was the species name used in the 1990 s and 2000 s.

Merizodus

Oopterus

Merizodus soledadinus

Chapter 4

Port-aux-Français in 2013-2014, are warmly thanked. Finally, we would like to thank two anonymous referees for their helpful comments on a previous version of our manuscript.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jinsphys.2016.08.006

Chapter 5 increased, and we conclude that this pattern most probably results from the suboptimal temperatures encountered during larval stages at altitudinal habitats. Indeed, thermal conditions from 200 m asl onwards progressively impact the overall physiology of this insect. These results suggest that climatic changes have preconditioned the invasion process of M. soledadinus in altitudinal habitats, as populations of this species were nearly absent at low altitudes before 2003, while the recorded mean air temperature increase of 1.7 °C between the mid-1960th and 20101.7 °C between the mid-1960th and (Lebouvier et al. 2011) have probably permitted the colonisation of altitudinal habitats. If temperature increase continues, this insect will have the possibility to flourish at its currently colonized altitudinal habitats, and could even progress and colonize higher altitudes, provided the availability of trophic resources.

General Discussion

The fast-growing populations of non-native arthropod species, their ecological niche shifts during invasion process, and their accelerating expanding ranges in the areas of introduction remain under deep investigation. In this thesis manuscript, I have focused on the main determinants assisting the invasion success of the predatory carabid beetle Merizodus soledadinus invading the Kerguelen Islands. Among the different factors hampering or assisting its ongoing invasion success, the performance of several biological traits including fecundity, longevity, stress resistance or dispersal in newly colonised regions is pivotal. Thus, several studies were undertaken to complete our knowledge of the factors supporting the range expansion of M. soledadinus at the Kerguelen Islands.

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Summary of the main results within the framework of this thesis

Chapter 1 -The long-living adults of M. soledadinus are year-round active and no egg-laying period exists

The first chapter of this dissertation focus on life history traits of this ground beetle in the introduced area that remained yet unexplored. The adult life span was determined under controlled conditions, the seasonal activity was monitored in natural conditions through regular pitfall trappings, and temporal variations of egg load and body reserves (glycogen, proteins, triglycerides) were analysed in wild individuals over an 18-month period (Chapter 1). The maximum adult lifespan reached 710 days, with half of the individuals surviving around 240 days in the experimental setting.

Females carry eggs evenly over the year (8.94 ± 3.56 eggs per female). It was not possible to pinpoint any clear egg-laying period from our data, thus questioning the earlier assumed semelparity of this species. Specimens were caught at each trapping session, demonstrating that activity is maintained year round in this predatory insect, but peaks were observed during the austral summer. Year-round trappings demonstrated the continuous activity of M. soledadinus over seasons, with a peak during Austral summer that may be associated with higher temperatures. Body stores (glycogen and proteins) did not vary significantly over the year, suggesting that adults feed continuously despite different prey availability between summer and winter, possibly via diet shifts. The amount of triglycerides increased at the onset of summer, and may be associated with the higher summer locomotor activity and/or more intense predation and reproduction.