Phylogenetic relatedness and proboscis length contribute to structuring bumblebee communities in the extremes of abiotic and biotic gradients

Aim To improve our understanding of how biological communities assemble, we investigated changes in bumblebee communities in space along an elevation gradient. We assessed how much deterministic abiotic and biotic factors shape community assembly. We focused on proboscis length (influencing the species' dietary regime) and phylogenetic relatedness to investigate if competition and environmental filtering occur in more and less productive climates, respectively. Location Western Swiss Alps. Methods We recorded bumblebee species in 149 plots along a 1800-m wide elevation gradient. We contrasted two major clades of bumblebees, a short-tongued and a long-tongued clade. We calculated the phylogenetic and proboscis-length diversity of the bumblebee communities and compared these observed data with a random distribution to detect clustering likely to be caused by environmental filtering or overdispersion likely to be caused by competition. We compared the prevalence of clustered and overdispersed communities along the gradients of plant species richness (biotic) and temperature (abiotic). Results Under colder conditions, where plant species richness is lower and floral resources are scarcer, the clade with shorter proboscides prevails over the clade with longer proboscides, and communities are functionally and phylogenetic clustered. Under warmer conditions, we found phylogenetic but not functional overdispersion in communities. Main conclusions We show for the first time a strong correlation between phylogenetic relatedness, proboscis length and species distribution along temperature and plant richness gradients shaping bumblebee communities. The low temperatures and low levels of plant species richness limit the dispersal of the species from the long-tongued clade, which have more specialized diets, into high-elevation areas. Competition under warmer conditions may produce communities composed of less closely related species that share distinct ecological preferences. Our empirical results corroborate theoretical expectation as well as experiments on the prevalence of deterministic processes in the most severe and most productive parts of environmental gradients.

Genetic differentiation for size at first reproduction through male versus female functions in the widespread Mediterranean tree Pinus pinaster.

BACKGROUND AND AIMS: The study of local adaptation in plant reproductive traits has received substantial attention in short-lived species, but studies conducted on forest trees are scarce. This lack of research on long-lived species represents an important gap in our knowledge, because inferences about selection on the reproduction and life history of short-lived species cannot necessarily be extrapolated to trees. This study considers whether the size for first reproduction is locally adapted across a broad geographical range of the Mediterranean conifer species Pinus pinaster. In particular, the study investigates whether this monoecious species varies genetically among populations in terms of whether individuals start to reproduce through their male function, their female function or both sexual functions simultaneously. Whether differences among populations could be attributed to local adaptation across a climatic gradient is then considered. METHODS: Male and female reproduction and growth were measured during early stages of sexual maturity of a P. pinaster common garden comprising 23 populations sampled across the species range. Generalized linear mixed models were used to assess genetic variability of early reproductive life-history traits. Environmental correlations with reproductive life-history traits were tested after controlling for neutral genetic structure provided by 12 nuclear simple sequence repeat markers. KEY RESULTS: Trees tended to reproduce first through their male function, at a size (height) that varied little among source populations. The transition to female reproduction was slower, showed higher levels of variability and was negatively correlated with vegetative growth traits. Several female reproductive traits were correlated with a gradient of growth conditions, even after accounting for neutral genetic structure, with populations from more unfavourable sites tending to commence female reproduction at a lower individual size. CONCLUSIONS: The study represents the first report of genetic variability among populations for differences in the threshold size for first reproduction between male and female sexual functions in a tree species. The relatively uniform size at which individuals begin reproducing through their male function probably represents the fact that pollen dispersal is also relatively invariant among sites. However, the genetic variability in the timing of female reproduction probably reflects environment-dependent costs of cone production. The results also suggest that early sex allocation in this species might evolve under constraints that do not apply to other conifers.

First-generation linkage map for the European tree frog (Hyla arborea) with utility in congeneric species.

BACKGROUND: Western Palearctic tree frogs (Hyla arborea group) represent a strong potential for evolutionary and conservation genetic research, so far underexploited due to limited molecular resources. New microsatellite markers have recently been developed for Hyla arborea, with high cross-species utility across the entire circum-Mediterranean radiation. Here we conduct sibship analyses to map available markers for use in future population genetic applications. FINDINGS: We characterized eight linkage groups, including one sex-linked, all showing drastically reduced recombination in males compared to females, as previously documented in this species. Mapping of the new 15 markers to the ~200 My diverged Xenopus tropicalis genome suggests a generally conserved synteny with only one confirmed major chromosome rearrangement. CONCLUSIONS: The new microsatellites are representative of several chromosomes of H. arborea that are likely to be conserved across closely-related species. Our linkage map provides an important resource for genetic research in European Hylids, notably for studies of speciation, genome evolution and conservation.

Functionally and phylogenetically diverse plant communities key to soil biota

Recent studies assessing the role of biological diversity for ecosystem functioning indicate that the diversity of functional traits and the evolutionary history of species in a community, not the number of taxonomic units, ultimately drives the biodiversity-ecosystem-function relationship. Here, we simultaneously assessed the importance of plant functional trait and phylogenetic diversity as predictors of major trophic groups of soil biota (abundance and diversity), six years from the onset of a grassland biodiversity experiment. Plant functional and phylogenetic diversity were generally better predictors of soil biota than the traditionally used species or functional group richness. Functional diversity was a reliable predictor for most biota, with the exception of soil microorganisms, which were better predicted by phylogenetic diversity. These results provide empirical support for the idea that the diversity of plant functional traits and the diversity of evolutionary lineages in a community are important for maintaining higher abundances and diversity of soil communities.

Modelling tree population dynamics at the alpine and boreal tree-line ecotones in response to climate and land-use change

Summary Ecotones are sensitive to change because they contain high numbers of species living at the margin of their environmental tolerance. This is equally true of tree-lines, which are determined by attitudinal or latitudinal temperature gradients. In the current context of climate change, they are expected to undergo modifications in position, tree biomass and possibly species composition. Attitudinal and latitudinal tree-lines differ mainly in the steepness of the underlying temperature gradient: distances are larger at latitudinal tree-lines, which could have an impact on the ability of tree species to migrate in response to climate change. Aside from temperature, tree-lines are also affected on a more local level by pressure from human activities. These are also changing as a consequence of modifications in our societies and may interact with the effects of climate change. Forest dynamics models are often used for climate change simulations because of their mechanistic processes. The spatially-explicit model TreeMig was used as a base to develop a model specifically tuned for the northern European and Alpine tree-line ecotones. For the latter, a module for land-use change processes was also added. The temperature response parameters for the species in the model were first calibrated by means of tree-ring data from various species and sites at both tree-lines. This improved the growth response function in the model, but also lead to the conclusion that regeneration is probably more important than growth for controlling tree-line position and species' distributions. The second step was to implement the module for abandonment of agricultural land in the Alps, based on an existing spatial statistical model. The sensitivity of its most important variables was tested and the model's performance compared to other modelling approaches. The probability that agricultural land would be abandoned was strongly influenced by the distance from the nearest forest and the slope, bath of which are proxies for cultivation costs. When applied to a case study area, the resulting model, named TreeMig-LAb, gave the most realistic results. These were consistent with observed consequences of land-abandonment such as the expansion of the existing forest and closing up of gaps. This new model was then applied in two case study areas, one in the Swiss Alps and one in Finnish Lapland, under a variety of climate change scenarios. These were based on forecasts of temperature change over the next century by the IPCC and the HadCM3 climate model (ΔT: +1.3, +3.5 and +5.6 °C) and included a post-change stabilisation period of 300 years. The results showed radical disruptions at both tree-lines. With the most conservative climate change scenario, species' distributions simply shifted, but it took several centuries reach a new equilibrium. With the more extreme scenarios, some species disappeared from our study areas (e.g. Pinus cembra in the Alps) or dwindled to very low numbers, as they ran out of land into which they could migrate. The most striking result was the lag in the response of most species, independently from the climate change scenario or tree-line type considered. Finally, a statistical model of the effect of reindeer (Rangifer tarandus) browsing on the growth of Pinus sylvestris was developed, as a first step towards implementing human impacts at the boreal tree-line. The expected effect was an indirect one, as reindeer deplete the ground lichen cover, thought to protect the trees against adverse climate conditions. The model showed a small but significant effect of browsing, but as the link with the underlying climate variables was unclear and the model was not spatial, it was not usable as such. Developing the TreeMig-LAb model allowed to: a) establish a method for deriving species' parameters for the growth equation from tree-rings, b) highlight the importance of regeneration in determining tree-line position and species' distributions and c) improve the integration of social sciences into landscape modelling. Applying the model at the Alpine and northern European tree-lines under different climate change scenarios showed that with most forecasted levels of temperature increase, tree-lines would suffer major disruptions, with shifts in distributions and potential extinction of some tree-line species. However, these responses showed strong lags, so these effects would not become apparent before decades and could take centuries to stabilise. Résumé Les écotones son sensibles au changement en raison du nombre élevé d'espèces qui y vivent à la limite de leur tolérance environnementale. Ceci s'applique également aux limites des arbres définies par les gradients de température altitudinaux et latitudinaux. Dans le contexte actuel de changement climatique, on s'attend à ce qu'elles subissent des modifications de leur position, de la biomasse des arbres et éventuellement des essences qui les composent. Les limites altitudinales et latitudinales diffèrent essentiellement au niveau de la pente des gradients de température qui les sous-tendent les distance sont plus grandes pour les limites latitudinales, ce qui pourrait avoir un impact sur la capacité des espèces à migrer en réponse au changement climatique. En sus de la température, la limite des arbres est aussi influencée à un niveau plus local par les pressions dues aux activités humaines. Celles-ci sont aussi en mutation suite aux changements dans nos sociétés et peuvent interagir avec les effets du changement climatique. Les modèles de dynamique forestière sont souvent utilisés pour simuler les effets du changement climatique, car ils sont basés sur la modélisation de processus. Le modèle spatialement explicite TreeMig a été utilisé comme base pour développer un modèle spécialement adapté pour la limite des arbres en Europe du Nord et dans les Alpes. Pour cette dernière, un module servant à simuler des changements d'utilisation du sol a également été ajouté. Tout d'abord, les paramètres de la courbe de réponse à la température pour les espèces inclues dans le modèle ont été calibrées au moyen de données dendrochronologiques pour diverses espèces et divers sites des deux écotones. Ceci a permis d'améliorer la courbe de croissance du modèle, mais a également permis de conclure que la régénération est probablement plus déterminante que la croissance en ce qui concerne la position de la limite des arbres et la distribution des espèces. La seconde étape consistait à implémenter le module d'abandon du terrain agricole dans les Alpes, basé sur un modèle statistique spatial existant. La sensibilité des variables les plus importantes du modèle a été testée et la performance de ce dernier comparée à d'autres approches de modélisation. La probabilité qu'un terrain soit abandonné était fortement influencée par la distance à la forêt la plus proche et par la pente, qui sont tous deux des substituts pour les coûts liés à la mise en culture. Lors de l'application en situation réelle, le nouveau modèle, baptisé TreeMig-LAb, a donné les résultats les plus réalistes. Ceux-ci étaient comparables aux conséquences déjà observées de l'abandon de terrains agricoles, telles que l'expansion des forêts existantes et la fermeture des clairières. Ce nouveau modèle a ensuite été mis en application dans deux zones d'étude, l'une dans les Alpes suisses et l'autre en Laponie finlandaise, avec divers scénarios de changement climatique. Ces derniers étaient basés sur les prévisions de changement de température pour le siècle prochain établies par l'IPCC et le modèle climatique HadCM3 (ΔT: +1.3, +3.5 et +5.6 °C) et comprenaient une période de stabilisation post-changement climatique de 300 ans. Les résultats ont montré des perturbations majeures dans les deux types de limites de arbres. Avec le scénario de changement climatique le moins extrême, les distributions respectives des espèces ont subi un simple glissement, mais il a fallu plusieurs siècles pour qu'elles atteignent un nouvel équilibre. Avec les autres scénarios, certaines espèces ont disparu de la zone d'étude (p. ex. Pinus cembra dans les Alpes) ou ont vu leur population diminuer parce qu'il n'y avait plus assez de terrains disponibles dans lesquels elles puissent migrer. Le résultat le plus frappant a été le temps de latence dans la réponse de la plupart des espèces, indépendamment du scénario de changement climatique utilisé ou du type de limite des arbres. Finalement, un modèle statistique de l'effet de l'abroutissement par les rennes (Rangifer tarandus) sur la croissance de Pinus sylvestris a été développé, comme première étape en vue de l'implémentation des impacts humains sur la limite boréale des arbres. L'effet attendu était indirect, puisque les rennes réduisent la couverture de lichen sur le sol, dont on attend un effet protecteur contre les rigueurs climatiques. Le modèle a mis en évidence un effet modeste mais significatif, mais étant donné que le lien avec les variables climatiques sous jacentes était peu clair et que le modèle n'était pas appliqué dans l'espace, il n'était pas utilisable tel quel. Le développement du modèle TreeMig-LAb a permis : a) d'établir une méthode pour déduire les paramètres spécifiques de l'équation de croissance ä partir de données dendrochronologiques, b) de mettre en évidence l'importance de la régénération dans la position de la limite des arbres et la distribution des espèces et c) d'améliorer l'intégration des sciences sociales dans les modèles de paysage. L'application du modèle aux limites alpines et nord-européennes des arbres sous différents scénarios de changement climatique a montré qu'avec la plupart des niveaux d'augmentation de température prévus, la limite des arbres subirait des perturbations majeures, avec des glissements d'aires de répartition et l'extinction potentielle de certaines espèces. Cependant, ces réponses ont montré des temps de latence importants, si bien que ces effets ne seraient pas visibles avant des décennies et pourraient mettre plusieurs siècles à se stabiliser.

Plant functional and phylogenetic turnover correlate with climate and land use in the Western Swiss Alps

Understanding the relative importance of historical and environmental processes in the structure and composition of communities is one of the longest quests in ecological research. Increasingly, researchers are relying on the functional and phylogenetic β-diversity of natural communities to provide concise explanations on the mechanistic basis of community assembly and the drivers of trait variation among species. The present study investigated how plant functional and phylogenetic β-diversity change along key environmental and spatial gradients in the Western Swiss Alps. Methods Using the quadratic diversity measure based on six functional traits: specific leaf area (SLA), leaf dry matter content (LDMC), plant height (H), leaf carbon content (C), leaf nitrogen content (N), and leaf carbon to nitrogen content (C/N) alongside a species-resolved phylogenetic tree, we relate variations in climate, spatial geographic, land use and soil gradients to plant functional and phylogenetic turnover in mountain communities of the Western Swiss Alps. Important findings Our study highlights two main points. First, climate and land use factors play an important role in mountain plant community turnover. Second, the overlap between plant functional and phylogenetic turnover along these gradients correlates with the low phylogenetic signal in traits, suggesting that in mountain landscapes, trait lability is likely an important factor in driving plant community assembly. Overall, we demonstrate the importance of climate and land use factors in plant functional and phylogenetic community turnover, and provide valuable complementary insights into understanding patterns of β-diversity along several ecological gradients.

Temporal and spatial dynamics of benthic invertebrate communities in an alpine glacier-fed alluvial system

Summary The present thesis work focused on the ecology of benthic invertebrates in the proglacial floodplain of the Rhone in the Swiss Alps. The main glacial Rhone River and a smaller glacial tributary, the Mutt River, joined and entered a braiding multi-thread area. A first part concentrated on the disruption of the longitudinal patterns of environmental conditions and benthic invertebrate fauna in the Rhone by its tributary the Mutt. The Mutt had less harsh environmental conditions, higher taxonomic richness and more abundant zoobenthos compared to the Rhone upstream of the confluence. Although the habitat conditions in the main stream were little modified by the tributary, the fauna was richer and more diverse below the confluence. Colonisation from the Mutt induced the occurrence of faunal elements uncommon of glacial streams in the upper Rhone, where water temperature remains below 4°C. Although the glacial Rhone dominated the system with regard to hydrology and certain environmental conditions, the Mutt tributary has to be seen as the faunal driver of the system. The second part of the study concerned the spatio-temporal differentiation of the habitats and the benthic communities along and across the flood plain. No longitudinal differentiation was found. The spatial transversal differentiation of three habitat types with different environmental characteristics was successfully reflected in the spatial variability of benthic assemblages. This typology separated marginal sites of the flood plain, left bank sites under the influence of the Mutt, and the right bank sites under the influence of the Rh6ne. Faunistic spatial differences were emphasized by the quantitative structure of the fauna, richness, abundances and Simpson index of diversity. Seasonal environmental variability was positively related with Simpson index of diversity and the total richness per site. Low flow conditions were the most favourable season for the fauna and November was characterized by low spatial environmental heterogeneity, high spatial heterogeneity of faunal assemblage, maximum taxonomic richness, a particular taxonomic composition, highest abundances, as well as the highest primary food resources. The third part studied the egg development of three species of Ephemeroptera in the laboratory at 1.5 to 7°C and the ecological implications in the field. Species revealed very contrasting development strategies. Baetis alpinus has a synchronous and efficient egg development, which is faster in warmer habitats, enabling it to exploit short periods of favourable conditions in the floodplain. Ecdyonurus picteti has a very long development time slightly decreasing in warmer conditions. The high degree of individual variation suggests a genetic determination of the degree-days demand. Combined with the glacial local conditions, this strategy leads to an extreme delay of hatching and allows it to develop in very unpredictable habitats. Rhithrogena nivata is the second cold adapted species in Ephemeroptera. The incubation duration is long and success largely depends on the timing of hatching and the discharge conditions. This species is able to exploit extremely unstable and cold habitats where other species are limited by low water temperatures. The fourth part dealt with larval development in different habitats of the floodplain. Addition of data on egg development allowed the description of the life histories of the species from oviposition until emergence. Rhithrogena nivata and loyolaea generally have a two-year development, with the first winter passed as eggs and the second one as larvae. Development of Ecdyonurus picteti is difficult to document but appears to be efficient in a harsh and unpredictable environment. Baetis alpinus was studied separately in four habitats of the floodplain system with contrasting thermal regimes. Differences in success and duration of larval development and in growth rates are emphasised. Subvention mechanisms between habitats by migration of young or grown larvae were demonstrated. Development success and persistence of the populations in the system were thus increased. Emergence was synchronised to the detriment of the optimisation of the adult's size and fecundity. These very different development strategies induce a spatial and temporal distribution in the use of food resources and ecological niches. The last part of this work aimed at the synthesis of the characteristics and the ecological features of three distinct compartments of the system that are the upper Rhone, the Mutt and the floodplain. Their particular role as well as their inter-dependence concerning the structure and the dynamics of the benthic communities was emphasised. Résumé Ce travail de thèse est consacré à l'écologie des invertébrés benthiques dans la zone alluviale proglaciaire du Rhône dans les Alpes suisses. Le Rhône, torrent glaciaire principal, reçoit les eaux de la Mutt, affluent glaciaire secondaire, puis pénètre dans une zone de tressage formée de plusieurs bras. La première partie de l'étude se concentre sur la disruption par la Mutt des processus longitudinaux, tant environnementaux que faunistiques, existants dans le Rhône. Les conditions environnementales régnant dans la Mutt sont moins rudes, la richesse taxonomique plus élevée et le zoobenthos plus abondant que dans le Rhône en amont de la confluence. Bien que les conditions environnementales dans le torrent principal soient peu modifiées par l'affluent, la faune s'avère être plus riche et plus diversifiée en aval de la confluence. La colonisation depuis la Mutt permet l'occurrence de taxons inhabituels dans le Rhône en amont de la confluence, où la température de l'eau se maintient en dessous de 4°C. Bien que le Rhône, torrent glaciaire principal, domine le système du point de vu de l'hydrologie et de certains paramètres environnementaux, l'affluent Mutt doit être considéré comme l'élément structurant la faune dans le système. La deuxième partie concerne la différentiation spatiale et temporelle des habitats et des communautés benthiques à travers la plaine alluviale. Aucune différentiation longitudinale n'a été mise en évidence. La différentiation transversale de trois types d'habitats sur la base des caractéristiques environnementales a été confirmée par la variabilité spatiale de la faune. Cette typologie sépare les sites marginaux de la plaine alluviale, ceux sous l'influence de la Mutt (en rive gauche) et ceux sous l'influence du Rhône amont (en rive droite). Les différences spatiales de la faune sont mises en évidence par la structure quantitative de la faune, la richesse, les abondances et l'indice de diversité de Simpson. La variabilité saisonnière du milieu est positivement liée avec l'indice de diversité de Simpson et la richesse totale par site. L'étiage correspond à la période la plus favorable pour la faune et novembre réunit des conditions de faible hétérogénéité spatiale du milieu, de forte hétérogénéité spatiale de la faune, une richesse taxonomique maximale, une composition faunistique particulière, les abondances ainsi que les ressources primaires les plus élevées. La troisième partie est consacrée à l'étude du développement des oeufs de trois espèces d'Ephémères au laboratoire à des températures de 1.5 à 7°C, ainsi qu'aux implications écologiques sur le terrain. Ces espèces présentent des stratégies de développement très contrastées. Baetis alpinus a un développement synchrone et efficace, plus rapide en milieu plus chaud et lui permettant d'exploiter les courtes périodes de conditions favorables. Ecdyonurus picteti présente une durée de développement très longue, diminuant légèrement dans des conditions plus chaudes. L'importante variation interindividuelle suggère un déterminisme génétique de la durée de développement. Cette stratégie, associée aux conditions locales, conduit à un décalage extrême des éclosions et permet à l'espèce de se développer dans des habitats imprévisibles. Rhithrogena nivata est la seconde espèce d'Ephémères présentant une adaptation au froid. L'incubation des oeufs est longue et son succès dépend de la période des éclosions et des conditions hydrologiques. Cette espèce est capable d'exploiter des habitats extrêmement instables et froids, où la température est facteur limitant pour d'autres espèces. La quatrième partie traite du développement larvaire dans différents habitats de la plaine alluviale. Le développement complet est décrit pour les espèces étudiées de la ponte jusqu'à l'émergence. Rhithrogena nivata et loyolaea atteignent généralement le stade adulte en deux ans, le premier hiver étant passé sous forme d'oeuf et le second sous forme de larve. Le développement de Ecdyonurus picteti est difficile à documenter, mais s'avère cependant efficace dans un environnement rude et imprévisible. Baetis alpinus a été étudié séparément dans quatre habitats de la plaine ayant des régimes thermiques contrastés. La réussite et la durée du développement embryonnaire ainsi que les taux de croissance y sont variables. Des mécanismes de subvention entre habitats sont possibles par la migration de larves juvéniles ou plus développées, augmentant ainsi la réussite du développement et le maintien des populations dans le système. L'émergence devient synchrone, au détriment de l'optimisation de la taille et de la fécondité des adultes. Ces stratégies très différentes induisent une distribution spatiale et temporelle dans l'usage des ressources et des niches écologiques. La dernière partie synthétise les caractéristiques écologiques des trois compartiments du système que sont le Rhône amont, la Mutt et la zone alluviale. Leurs rôles particuliers et leurs interdépendances du point de vue de la structure et de la dynamique des communautés benthiques sont mis en avant.

Characterising avian haemosporidian communities : ecological factors, parasite persistence and co-infection

Les parasites jouent un rôle clef dans l'évolution des comportements et des traits d'histoire de vie de leurs hôtes. Le parasitisme s'avère parfois dévastateur à l'échelle de population d'hôtes, et peut également altérer certains traits associés à la valeur sélective d'un individu infecté, tels que son succès reproducteur ou encore son taux de mortalité. La coévolution hôte/parasite, qui représente l'une des forces sélectives les plus puissantes dans l'évolution des organismes, peut également conduire les partenaires de l'association parasitaire à s'adapter localement à des environnements hétérogènes. Cette thèse porte sur l'étude de parasites aviaires, du genre Plasmodium, Haemopro- teus et Leucocytozoon (Haemosporidae), naturellement associés à différentes populations de mésanges charbonnières (Parus major) et d'hirondelles des fenêtres (Delichon ur- bicum). Dans un premier temps, nous avons cherché à déterminer comment se distribuent ces parasites au sein de différentes populations hôtes et si ces communautés de parasites sont structurées. Par la suite, la principale question à laquelle nous voulions répondre était de savoir comment ces parasites, et notamment après coexistence de plusieurs lignées génétiques d'Haemosporidae au sein dun même-individu (i.e. co-infection), affectent la physiologie et le succès de reproducteur des hôtes. Nos résultats suggèrent que la distribution des Haemosporidae est principalement gouvernée par la présence d'insectes vecteurs et que la persistance de l'infection chez les hôtes varie en fonction du genre d'Haemosporidae (Chapitre 1-2). Par ailleurs, nous avons trouvé que des lignées de parasite génétiquement distinctes peuvent avoir des effets contrastés sur leurs hôtes. Par exemple, les hôtes exhibent des différences de parasitémie marquées en fonction des lignées de parasites responsable de l'infection. De plus, le succès reproducteur ainsi que la charge parasitaire des mésanges infectées par Plasmodium ou Haemoproteus n'étaient pas affecté par l'infection simultanée avec Leucocytozoon (Chapitre 2-3). Dans le Chapitre 4, j'ai examiné la capacité immunitaire de mésanges charbonnières infectées par des hémosporidies. Les résultats n'ont pas été concluant, et je suggère fortement une réévaluation de ceux-ci dans de futures études. Les mésanges charbonnières ne semblent pas signaler leur statut infectieux par la coloration de leur plumage (Chapitre 5); toutefois, la coloration noire des plumes reflète l'état de stress oxydatif des mésanges, qui dépend lui-même de l'infection parasitaire. La coloration verte pourrait également indiquer la qualité des soins paxentaux délivrés par les mésanges adultes femelles à leurs petits, comme le suggère la corrélation que nous avons observée entre la masse des jeunes d'une nichée et la coloration de leur mère. Les hirondelles capturées en Algérie souffrent plus de l'infection que celles échantillon¬nées en Europe (Chapitre 6). Les similitudes observées entre les communautés de par¬asites affectant les populations européennes et celles des populations nord-africaines suggèrent que la transmission des parasites a lieu lors de la migration vers le sud. A l'instar de nos observations sur les mésanges dans les chapitres 2 et 3, les hirondelles co-infectées ne montrent pas d'altérations de leur condition physique. Cette thèse démontre qu'il existe, au sein des populations de mésanges charbonnières, des interactions antagonistes entre, d'une part, les parasites et leurs hôtes et d'autre part, entre différent parasites. Le résultat de ces interactions antagonistes varie en fonction des espèces et de la zone géographique considérée. Nous avons démontré que les interactions ne suivent pas toujours la théorie, puisque la coevolution qui, en suivant le concept de la virulence, devrait augmenter la charge parasitaire et diminuer la condition physique des hôtes, ne montre pourtant pas d'impact négatif sur les populations de mésanges. Nous pouvons maintenant concentrer nos efforts à la caractérisation des interactions antagonistes. De plus, grâce aux avancées des méthodes moléculaires, nous pouvons suivre et étudier en détails comment ces interactions se manifestent et quels sont leurs effets sur la condition physique des hôtes. - Parasites are key in shaping various behavioural and life-history traits of their hosts. The influence of parasitism on host populations varies from slight to devastating and might influence such parameters as mortality rates or reproductive success. Host-parasite coevolution is one of the most powerful selective forces in evolution and can lead to local adaptation of parasites and hosts in spatially structured environments. In this thesis, I studied haemosporidian parasites in different populations of great tits (Parus major) and house martins (Delichon urbicum). Firstly, I wanted to determine how parasites are distributed and if parasite communities are structured. The main question I wanted to address hereafter was how parasites, and specifically infection with multiple genera of parasites (i.e. co-infection) influenced host physiology and reproductive success. I found that parasite distribution is environmentally driven and could therefore be closely linked to vector prevalence; and that the stability of parasite infection over time is genus-dependent (Chapter 1 - 2). I further found that different haemosporidian lineages might interact differently with their hosts as parasitaemia was strongly lineage-specific and that the presence of Leucocytozoon parasites showed no correlation to Plasmodium or Haemoproteus parasitaemia, nor to great tit reproductive success (Chapter 2-3). In Chapter 4 I examined immune capacity of haemosporidian-infected great tits. The results proved inconclusive, and I strongly suggest re-evaluation hereof in future work. Great tits do not appear to signal parasite infection through plumage colouration (Chapter 5); however, infection did have a link to oxidative stress resistance which is strongly signalled through the black breast stripe, with darker males being more resistant and darker females less resistant. Females might incur different costs associated with darker stripes. This would allow reversal of signaling function. Green colouration could also serve as a cue for female provisioning quality as indicated by the strong correlation between colouration and chick body mass. Breeding house martins caught in Algeria suffer greater haemosporidian infection than European populations (Chapter 6). Similar parasite communities in European and North-African populations suggest transmission of parasites may occur during southward migration. Similarly to what was observed in great tits in Chapter 2 and 3, no relationship was found between parasite co-infection and Swiss house martin body condition. This thesis demonstrates that host-parasite and inter-parasite antagonistic interac¬tions exist in great tit populations. How these interactions play out is species dependent and varies geographically. I have demonstrated that interactions do not always follow the theory, as co-infection - which under the concept of virulence should increase parasitaemia and decrease body condition - showed no negative impact on great tit populations. We can now concentrate our efforts on characterising these antagonistic interactions, and with the advance in molecular methods, track and investigate how these interactions play out and what the effect on host fitness is.

Sex-chromosome differentiation parallels postglacial range expansion in European tree frogs (Hyla arborea).

Occasional XY recombination is a proposed explanation for the sex-chromosome homomorphy in European tree frogs. Numerous laboratory crosses, however, failed to detect any event of male recombination, and a detailed survey of NW-European Hyla arborea populations identified male-specific alleles at sex-linked loci, pointing to the absence of XY recombination in their recent history. Here, we address this paradox in a phylogeographic framework by genotyping sex-linked microsatellite markers in populations and sibships from the entire species range. Contrasting with postglacial populations of NW Europe, which display complete absence of XY recombination and strong sex-chromosome differentiation, refugial populations of the southern Balkans and Adriatic coast show limited XY recombination and large overlaps in allele frequencies. Geographically and historically intermediate populations of the Pannonian Basin show intermediate patterns of XY differentiation. Even in populations where X and Y occasionally recombine, the genetic diversity of Y haplotypes is reduced below the levels expected from the fourfold drop in copy numbers. This study is the first in which X and Y haplotypes could be phased over the distribution range in a species with homomorphic sex chromosomes; it shows that XY-recombination patterns may differ strikingly between conspecific populations, and that recombination arrest may evolve rapidly (<5000 generations).

Spatial pattern and process at the plant neighbourhood scale: insights from communities dominated by the clonal grass Elymus repens (L.) Gould.

Question: How do clonal traits of a locally dominant grass (Elymus repens (L.) Gould.) respond to soil heterogeneity and shape spatial patterns of its tillers? How do tiller spatial patterns constrain seedling recruitment within the community?Locations: Artificial banks of the River Rhone, France.Material and Methods: We examined 45 vegetation patches dominated by Elymus repens. During a first phase we tested relationships between soil variables and three clonal traits (spacer length, number of clumping tillers and branching rate), and between the same clonal traits and spatial patterns (i.e. density and degree of spatial aggregation) of tillers at a very fine scale. During a second phase, we performed a sowing experiment to investigate effects of density and spatial patterns of E. repens on recruitment of eight species selected from the regional species pool.Results: Clonal traits had clear effects - especially spacer length - on densification and aggregation of E. repens tillers and, at the same time, a clear response of these same clonal traits as soil granulometry changed. The density and degree of aggregation of E. repens tillers was positively correlated to total seedling cover and diversity at the finest spatial scales.Conclusions: Spatial patterning of a dominant perennial grass responds to soil heterogeneity through modifications of its clonal morphology as a trade-off between phalanx and guerrilla forms. In turn, spatial patterns have strong effects on abundance and diversity of seedlings. Spatial patterns of tillers most probably led to formation of endogenous gaps in which the recruitment of new plant individuals was enhanced. Interestingly, we also observed more idiosyncratic effects of tiller spatial patterns on seedling cover and diversity when focusing on different growth forms of the sown species.

Does the generalist parasitic plant Cuscuta campestris selectively forage in heterogeneous plant communities?

Cuscuta spp. are holoparasitic plants that can simultaneously parasitise several host plants. It has been suggested that Cuscuta has evolved a foraging strategy based on a positive relationship between preuptake investment and subsequent reward on different host species. Here we establish reliable parasite size measures and show that parasitism on individuals of different host species alters the biomass of C. campestris but that within host species size and age also contributes to the heterogeneous resource landscape. We then performed two additional experiments to test whether C. campestris achieves greater resource acquisition by parasitising two host species rather than one and whether C. campestris forages in communities of hosts offering different rewards (a choice experiment). There was no evidence in either experiment for direct benefits of a mixed host diet. Cuscuta campestris foraged by parasitising the most rewarding hosts the fastest and then investing the most on them. We conclude that our data present strong evidence for foraging in the parasitic plant C. campestris.

Functional homogenization of bumblebee communities in alpine landscapes under projected climate change

Background: Bumblebees represent an active pollinator group in mountain regions and assure the pollination of many different plant species from low to high elevations. Plant-pollinator interactions are mediated by functional traits. Shift in bumblebee functional structure under climate change may impact plant-pollinator interactions in mountains. Here, we estimated bumblebee upward shift in elevation, community turnover, and change in functional structure under climate change. Method: We sampled bumblebee species at 149 sites along the elevation gradient. We used stacked species distribution models (S-SDMs) forecasted under three climate change scenarios (A2, A1B, RCP3PD) to model the potential distribution of the Bombus species. Furthermore, we used species proboscis length measurements to assess the functional change in bumblebee assemblages along the elevation gradient. Results: We found species-specific response of bumblebee species to climate change. Species differed in their predicted rate of range contraction and expansion. Losers were mainly species currently restricted to high elevation. Under the most severe climate change scenarios (A2), we found a homogenization of proboscis length structure in bumblebee communities along the elevation gradient through the upward colonization of high elevation by species with longer proboscides. Conclusions: Here, we show that in addition to causing the shift in the distribution of bumblebee species, climate change may impact the functional structure of communities. The colonization of high elevation areas by bumblebee species with long proboscides may modify the structure of plant-pollination interaction networks by increasing the diversity of pollination services at high elevation.

Diversity and structure of AMF communities as affected by tillage in a temperate soil.

Arbuscular mycorrhizal fungi (AMF) were studied in differently tilled soils from a long-term field experiment in Switzerland. Diversity and structure of AMF communities were surveyed either directly on spores isolated from the field soil or on spores isolated from trap cultures, planted with different host plants. Single-spore cultures were established from the AMF spores obtained from trap cultures. Identification of the AMF was made by observation of spore morphology and confirmed by sequencing of ITS rDNA. At least 17 recognised AMF species were identified in samples from field and/or trap cultures, belonging to five genera of AMF--Glomus, Gigaspora, Scutellospora, Acaulospora, and Entrophospora. Tillage had a significant influence on the sporulation of some species and non- Glomus AMF tended to be more abundant in the no-tilled soil. The community structure of AMF in the field soil was significantly affected by tillage treatment. However, no significant differences in AMF diversity were detected among different soil tillage treatments. AMF community composition in trap cultures was affected much more by the species of the trap plant than by the original tillage treatment of the field soil. The use of trap cultures for fungal diversity estimation in comparison with direct observation of field samples is discussed.