O dimensionamento da tecnologia trouxe consequências indesejáveis para manter a taxa de crescimento exponencial e levanta questões importantes relacionadas com a confiabilidade e robustez dos sistemas eletrônicos. Atualmente, microprocessadores modernos de superpipeline normalmente contêm milhões de dispositivos com cargas nos nós cada vez menores. Esse fator faz com que os circuitos sejam mais sensíveis a variabilidade ambiental e aumenta a probabilidade de um erro transiente acontecer. Erros transientes em circuitos sequenciais ocorrem quando uma única partícula energizada deposita carga suficiente perto de uma região sensível. Flip-Flops mestreescravo são os circuitos sequencias mais utilizados em projeto VLSI para armazenamento de dados. Se um bit-flip ocorrer dentro deles, eles perdem a informação prévia armazenada e podem causar um funcionamento incorreto do sistema. A fim de proporcionar sistemas mais confiáveis que possam lidar com os efeitos da radiação, este trabalho analisa o Fator de Vulnerabilidade Temporal (Timing Vulnerability Factor - TVF) em algumas topologias de flip-flops mestre-escravo em estágios de pipeline sob diferentes condições de operação. A janela de tempo efetivo que o bit-flip ainda pode ser capturado pelo próximo estágio é definido com janela de vulnerabilidade (WOV). O TVF corresponde ao tempo que o flip-flop é vulnerável a erros transientes induzidos pela radiação de acordo com a WOV e a frequência de operação. A primeira etapa deste trabalho determina a dependência entre o TVF com a propagação de falhas até o próximo estágio através de uma lógica combinacional com diferentes atrasos de propagação e com diferentes modelos de tecnologia, incluindo também as versões de alto desempenho e baixo consumo. Todas as simulações foram feitas sob as condições normais pré-definidas nos arquivos de tecnologia. Como a variabilidade se manifesta com o aumento ou diminuição das especificações iniciais, onde o principal problema é a incerteza sobre o valor armazenado em circuitos sequenciais, a segunda etapa deste trabalho consiste em avaliar o impacto que os efeitos da variabilidade ambiental causam no TVF. Algumas simulações foram refeitas considerando variações na tensão de alimentação e na temperatura em diferentes topologias e configurações de flip-flops mestre-escravo. Para encontrar os melhores resultados, é necessário tentar diminuir os valores de TVF, pois isso significa que eles serão menos vulneráveis a bit-flips. Atrasos de propagação entre dois circuitos sequenciais e frequências de operação mais altas ajudam a reduzir o TVF. Além disso, estas informações podem ser facilmente integradas em ferramentas de EDA para ajudar a identificar os flip-flops mestre-escravo mais vulneráveis antes de mitigar ou substituí-los por aqueles tolerantes a radiação. / Technology scaling has brought undesirable issues to maintain the exponential growth rate and it raises important topics related to reliability and robustness of electronic systems. Currently, modern super pipelined microprocessors typically contain many millions of devices with ever decreasing load capacitances. This factor makes circuits more sensitive to environmental variations and it is increased the probability to induce a soft error. Soft errors in sequential circuits occur when a single energetic particle deposits enough charge near a sensitive node. Master-slave flip-flops are the most adopted sequential elements to work as registers in pipeline and finite state machines. If a bit-flip happens inside them, they lose the previous stored information and may cause an incorrect system operation. To provide reliable systems that can cope with radiation effects, this work analysis the Timing Vulnerability Factor (TVF) of some master-slave D flip-flops topologies in pipeline stages under different operating conditions. The effective time window, which the bit-flip can still be captured by the next stage, is defined as Window of Vulnerability (WOV). TVF corresponds to the time that a flip-flop is vulnerable to radiation-induced soft errors according to WOV and clock frequency. In the first step of this work, it is determined the dependence between the TVF with the fault propagation to the next stage through a combinational logic with different propagation delays and with different nanometer technological models, including also high performance and low power versions. All these simulations were made under the pre-defined nominal conditions in technology files. The variability manifests with an increase or decreases to initial specification, where the main problem is the uncertainty about the value stored in sequential. In this way, the second step of this work evaluates the impact that environmental variability effect causes in TVF. Some simulations were redone considering supply voltage and temperature variations in different master-slave D flip-flop topologies configurations. To achieve better results, it is necessary to try to decrease the TVF values to reduce the vulnerability to bit-flips. The propagation delay between two sequential elements and higher clock frequencies collaborates to reduce TVF values. Moreover, all the information can be easily integrated into Electronic Design Automation (EDA) tools to help identifying the most vulnerable master-slave flip-flops before mitigating or replacing them by radiation hardened ones.

Many animal species invest in extended parental care for their offspring. Parental care is costly, and natural selection favors investment strategies which maximize reproductive success. Biparental care is relatively rare, but when it does occur it has been found to increase success in terms of offspring survival and growth and in terms of future reproductive opportunities. In burying beetles (<i>Nicrophorus</i> spp.), both male and female participate in extended parental care. However, the fitness benefits of biparental care in burying beetles have been difficult to establish, with some studies reporting significantly smaller broods produced when both male and female are present. Variation in environmental conditions, such as temperature, is an important part of the context in which biparental care evolves. I hypothesize that biparental care acts as a buffer against environmental variation. This hypothesis predicts that biparental care will lead to greater reproductive success compared to uniparental care when temperature is increased during a reproductive attempt. I also tested the load-lightening hypothesis, which holds that biparental care benefits future reproduction by lowering the costs of reproduction. This predicts that the additional care by the other parent will allow females to rear higher quality second broods. I conducted a male removal experiment at two temperature treatments, using the species <i>Nicrophorus orbicollis</i>. I measured reproductive success during manipulated first brood and during second broods which females reared without a male, regardless of prior experience. I found that, contrary to my hypothesis, biparental care at the higher temperature resulted in reduced reproductive success compared to uniparental care. I found no effect of biparental care on the success of second broods. Instead, I found evidence of reproductive restraint associated with the higher temperature treatment in delayed egg-laying and increased feeding during second broods.

Les travaux de cette thèse se sont situés autour de la relation entre discrimination isotopique du carbone 13 et échanges gazeux foliaires. Le modèle établi par Farquhar et al. (1982) permet de prédire la discrimination contre le 13C pendant la photosynthèse (delta13C) en tenant compte des processus de diffusion, de carboxylation et décarboxylation engagés pendant la photosynthèse. Cette relation permet d'utiliser delta13C comme indicateur de l'efficience d'utilisation de l'eau (WUE, quantité de carbone fixé en fonction de l'eau consommée), un paramètre particulièrement important dans un contexte de changement climatique, d'agriculture et de sylviculture. Le modèle de delta13C a également été utilisé pour estimer la conductance mésophyllienne au CO2 (gm), un paramètre qui limite fortement la photosynthèse via la disponibilité en carbone dans le chloroplaste. Au cours de nos travaux, nous avons analysé le modèle delta13C pour identifier les paramètres les plus influents dans le modèle, et mis en évidence que l'utilisation du "modèle simple" de delta13C (ignorant gm et les processus de décarboxylation) peut induire un biais important dans l'estimation de WUE. Dans un second temps nous nous sommes concentrés sur les possibles variations à court-terme de gm, un domaine encore sujet a débat. Nous avons confirmé que gm était sensible aux variations de CO2 et d'irradiance sur toutes les espèces d'arbres mesurées dans cette étude. Nous avons aussi montré que ces variations rapides ne peuvent pas être dues a des variations des autres paramètres du modèle, à l'exception possible du paramètre b (discrimination pendant la carboxylation). Nous suggérons que les prochaines études dans ce domaine portent sur (i) la possible variabilité environnementale et génétique du paramètre b et (ii) les mécanismes à l'origine des variations rapides de gm (aquaporines et anhydrases carboniques) / This work was focused on the relationship between isotopic discrimination of 13C during photosynthesis (delta13C) and leaf gas exchange. The model of Farquhar and colleagues (Farquhar et al. 1982) predicts delta13C by accounting for diffusion, carboxylation and decarboxylation processes during the photosynthesis. This relationship is widely used and delta13C is frequently considered as a proxy water use efficiency (WUE, the amount of water required to fix a amount of carbon), an interesting parameter in the context of climate change, crop production and sylviculture. The delta13C model is also used to assess mesophyll conductance to CO2 (gm), that strongly limits photosynthesis via the availability of carbon in the chloroplast. Along this work we analyzed the delta13C model and identified the most important parameters, and highlighted that using the "simple form" of the model (which ignores gm and the decarboxylations) could lead to misestimating WUE. We also focused on the possible rapid variations of gm, a subject still under debate. We confirmed that gm was sensitive to rapid variations of CO2 and irradiance in all species tested in this study. We also showed that apparent rapid variations of gm could not be induced by variations of other parameters in the model, with the exception of parameter b (discrimination during carboxylation). We propose that future studies should focus on (i) the possible environmental and genetic variability of parameter b, and (ii) the physiological processes able to change gm at short time scales (aquaporins and carbonic anhydrase).

Le but de cette thèse est d'étudier les comportements individuels liés à la sélection de l'habitat de reproduction chez un oiseau marin colonial longévif, la mouette tridactyle et de déterminer leur importance dans la réponse des populations aux changements environnementaux à différentes échelles spatiales et temporelles. Dans un premier temps, des approches expérimentales incluant un suivi du mouvement des individus par GPS et balises Argos ont permis de démontrer que seuls des individus en échec de reproduction effectuent des mouvements de prospection impliquant la visite d'autres zones de reproduction. Ces mouvements ont été enregistrés depuis la période de fin d'incubation jusqu'à la période d'élevage des poussins à des échelles spatiales aussi bien locales (<1km) que régionales (> 40 km), dans des conditions environnementales variées. Ensuite, un modèle de dynamique des populations considérant différentes stratégies de dispersion a montré que contrairement à la philopatrie et la dispersion aléatoire, l'utilisation d'informations personnelle et sociale par les individus permet aux populations de maintenir des effectifs élevés et de persister sur le long-terme. Enfin, des modèles de captures-recaptures ont mis en évidence des interactions indirectes entre protocoles de suivis à long-terme d'individus marqués et comportements individuels liés à la dispersion. Ces interactions peuvent notamment biaiser l'estimation de paramètres démographiques tels que le taux de survie annuelle. L'ensemble de nos résultats démontre que la sélection de l'habitat de reproduction et la dispersion sont des processus complexes mais essentiels dans la compréhension du fonctionnement des populations et qu'ils doivent être mieux pris en compte dans les modèles prédictifs de dynamique, structure et persistance des populations en réponse aux changements environnementaux. / The aim of this thesis is to study individual behaviours linked to breeding habitat selection in a long-lived colonial seabird, the black-legged kittiwake, and to determine their importance in population responses to environmental changes occurring at different spatial and temporal scales. First, experimental approaches including GPS and satellite tracking of individuals allowed demonstrating that only failed breeders performed prospecting movements involving visits of other breeding areas. These movements were recorded from egg incubation to chick rearing at local spatial scales (<1 km) as well as large spatial scales (> 40km), in various environmental conditions. Then, a population dynamic model considering different dispersal strategies showed that contrarily to philopatry and random dispersal, personal and social information use by individuals favoured population persistence in the long-term. Finally, capture-recapture models highlighted indirect interactions between sampling designs of long-term surveys of marked individuals and behaviours linked to dispersal. These interactions can notably bias the estimation of demographic parameters such as annual survival rate. All our results demonstrate that breeding habitat selection and dispersal are complex but essential processes in the understanding of population functioning and they have to be considered in models predicting the dynamics, structure and persistence of populations in response to environmental changes.

L’Arctique se réchauffe deux fois plus vite que le reste du monde, entrainant des changements majeurs des écosystèmes marins. Par exemple, l’étendue de la banquise diminue, et la distribution des masses d’air change, modifiant les régimes de vents et de précipitations. Parallèlement à ces changements climatiques, l’Arctique est soumise à une pollution anthropique croissante amenée par les circulations atmosphériques et océaniques, et accentuée par le développement des activités humaines locales. Dans ce contexte, il est urgent de comprendre les impacts écologiques de ces modifications environnementales sur les espèces de cette région. Les mergules nains (Alle alle) sont les oiseaux marins les plus abondants de l’Arctique, et des acteurs clés des réseaux trophiques côtiers. Bien que des travaux récents aient suggéré une forte résilience de ces organismes aux changements globaux, une étude approfondie permettant de comprendre de manière détaillée l’impact de ces changements était essentielle. Au cours de ce travail de thèse, nous avons donc utilisé une approche pluridisciplinaire (écologie alimentaire, écotoxicologie, bioénergétique, écologie du déplacement) menée à long terme afin de caractériser la sensibilité des mergules nains aux changements de leur environnement pendant la saison de reproduction (été) et en hiver. Nous avons pour cela étudié une population de mergules nains au Groenland Est. Nos résultats montrent que les mergules sont fortement impactés par les changements en cours. Pendant la période de reproduction, leurs proies changent et leur effort de plongée augmente en l’absence de banquise, même s’ils demeurent fidèles à leur zone de nourrissage sur le talus continental. Ceci tend à diminuer leur condition corporelle et celle de leur poussin, mais n’impacte pas leur survie. En hiver, les mergules nains optimisent leur migration et leur distribution en fonction de la distribution de leurs proies et de leur paysage énergétique. Ainsi, nos modèles prédictifs indiquent qu’un réchauffement de l’Atlantique nord pourrait être bénéfique pour les populations en diminuant leurs besoins énergétiques. Enfin, nous avons trouvé que les mergules nains consomment des microplastiques, et ce en les confondant avec leurs proies. Cette source de pollution supplémentaire pourrait augmenter avec la fonte de la banquise qui libère des microplastiques jusque-là stockés dans la glace. Ce travail souligne l’importance des programmes à long terme pour l’étude des impacts des changements globaux. / The Arctic is warming twice faster than the rest of the world, leading to major changes for marine ecosystems. For example, sea-ice extent is decreasing, and air mass distribution is changing, thus modifying wind and precipitation regimes. In parallel, the Arctic is subject to increasing anthropogenic pollution carried by atmospheric and oceanic circulation, and accentuated by the development of local human activities. In this context, there is an urgent need to understand the ecological impacts of these environmental modifications on the species of this region. Little auks (Alle alle) are the most abundant seabird in the Arctic, and key players of coastal food webs. Although recent works suggested a high resiliency of little auks to global changes, a comprehensive study was needed to understand in detail the impacts of these changes. Through this work, we used a multidisciplinary approach (diet ecology, ecotoxicology, bioenergetics, foraging ecology) on the long term to characterize little auk sensitivity to environmental changes during the breeding season (summer) and in winter. We therefore studied a little auk population in East Greenland. Our results show that little auks are indeed impacted by ongoing changes. During the breeding season, their prey change and their diving effort increase when there is no sea-ice, even if they remain faithful to their feeding grounds on the continental slope. This tends to decrease their body condition and that of their chick, but does not impact their survival. In winter, little auks optimize their migration and their distribution according to the distribution of their prey and their energetic landscape. Therefore, our predictive models indicate that a warming of the North Atlantic could be benefic for little auk populations, by reducing their energetic needs. Finally, we found that little auks ingest microplastics, by confusing them with their prey. This additional source of pollution could increase with sea-ice loss that release microplastics stocked in the ice. This work underlines the importance of long term monitoring programs for the study of global change impacts.

Paleoenvironmental investigations establish important baseline knowledge of the natural variability of lake systems, to better understand human impacts on the landscape, and the effects of climate change on water resources. By combining long-term environmental history with investigations into modern land use patterns and climatological events, a wider perspective can be reached that has practical applications in water governance. This thesis presents a case study of Lake Basotu (4.37°S, 35.07°E), a crater lake in the Hanang district of north-central Tanzania, which acts as an important source of freshwater for local people. A three-meter long sediment core from an interior crater of Lake Basotu was investigated using proxy records (diatoms, magnetic parameters, and carbon content) and radiometric dating (14C and 210Pb). The Lake Basotu record was then compared to other sediment-based reconstructions from East Africa and records of historical famines to better place it into the timeline and understanding of regional climate dynamics. This work was extended into modern times (1973–2015) by examining lake extent variations in the Landsat satellite archive. Shoreline boundaries for dry-season images were delineated and lake extent was calculated using GIS techniques. This remote sensing record was compared to climatological patterns, meteorological records, and the history of land-use changes in the surrounding district. As a whole, the Lake Basotu record indicates that major fluctuations in lake level are not abnormal; however, human influence has likely increased the lake’s sensitivity to climatic fluctuations. The timing of historical famines in East Africa were linked to periods of shallow lake conditions in Basotu, and the duration of the most extreme lake level changes correlate to a reversal in the 14C age-depth model. Recent variations in lake extent are likely connected to a mechanized wheat farming program implemented in the district as a foreign aid project in the early 1960s. To support the work done in Basotu, a preliminary investigation of sediment from the nearby Lake Babati was undertaken. Sediment from the two lakes indicates that their geographical location may be in a transition zone towards dryer conditions to the south during the Little Ice Age in East Africa. The results of this thesis support that Lake Basotu is an important location for understanding the potential impacts of climate change and human activity on water resources in this region. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 3: Manuscript.</p>

Understanding how temperature affects biological systems is a central question in ecology and evolutionary biology. Anthropogenic climate change adds urgency to this topic, as the demise or success of species under climate change is expected to depend on how temperature affects important aspects of organismal performance, such as growth, development, survival and reproduction. Rates of biological processes generally increase with increasing temperature up to some maximal temperature. Variation in the slope of the initial, rising phase has attracted considerable interest and forms the focus of this thesis. I explore variation in growth rate-temperature relationships over several levels of biological organization, both between and within species, over individuals’ lifetime, depending on the ecological context and in relation to important life history characteristics such as generation length and winter dormancy.       Specifically, I examine how a clade of temperate damselflies have adapted to their thermal environment along a 3,600 km long latitudinal transect spanning from Southern Spain to Northern Sweden. For each of six species, I sampled populations from close to the northern and southern range margin, as well from the center of the latitudinal range. I reared larvae in the laboratory at several temperatures in order to measure indiviudal growth rates. Very few studies of thermal adaptation have employed such an extensive sampling approach, and my finding reveal variation in temperature responses at several levels of organization.       My main finding was that temperature responses became steeper with increasing latitude, both between species but also between latitudinal populations of the same species. Additional genetic studies revealed that this trend was maintained despite strong gene flow. I highlight the need to use more refined characterizations of latitudinal temperature clines in order to explain these findings. I also show that species differ in their ability to acclimate to novel conditions during ontogeny, and propose that this may reflect a cost-benefit trade-off driven by whether seasonal transitions occur rapidly or gradually during ontogeny.       I also carried out a microcosm experiment, where two of the six species were reared either separately or together, to determine the interacting effects of temperature and competition on larval growth rates and population size structure. The results revealed that the effects of competition can be strong enough to completely overcome the rate-depressing effects of low temperatures. I also found that competition had stronger effects on the amount of variation in growth rates than on the average value.       In summary, my thesis offers several novel insights into how temperature affects biological systems, from individuals to populations and across species’ ranges. I also show how it is possible to refine our hypotheses about thermal adaptation by considering the interacting effects of ecology, life history and environmental variation.

Au cours de ces deux dernières décennies, la culture du pétoncle (Argopecten purpuratus) s’est développée dans les baies côtières péruviennes. La disponibilité trophique liée au système d’upwelling est favorable à la production du pétoncle. Cependant, les côtes péruviennes sont également connues pour présenter une forte variabilité environnementale surtout en domaine océanique. Bien que les élevages du pétoncle soient vulnérables aux aléas de production (mortalité, croissance faible), la variabilité environnementale dans les baies côtières du Pérou et ses effets sur la croissance, la reproduction et survie de cette ressource socialement sensible ont été peu étudiées. La baie de Paracas au Pisco-Pérou est une zone traditionnelle de culture du pétoncle où des hauts et des bas productifs liés aux conditions environnementales ont été enregistrés au long de son histoire. Dans le but d’approfondir nos connaissances sur cette problématique, cette étude se pose sous trois approches : (1) l’observation in situ, (2) l’expérimentation en physiologie et (3) la modélisation du bilan énergétique de A. Purpuratus. Un suivi environnemental mené dans la baie de Paracas montre que la variabilité océanographique peut être importante, en particulier pendant l’été. Des variations de température de 8°C et des conditions oxiques allant de la sursaturation à l’anoxie (absence d’oxygène) dans le cours d’une journée ont été observées. L’enregistrement haute fréquence a permis de révéler une exposition chronique, sévère et prolongée de la baie de Paracas aux conditions hypoxiques. Les pétoncles cultivés sur le fond, où l’exposition à l’hypoxie était importante (47% du temps observé) ont montré une croissance et les conditions de reproduction plus faibles. Cependant, au cours de l’été, les événements hypoxiques prolongés et sévères ont touché les deux profondeurs de culture- les pétoncles cultivés en suspension comme sur le fond-, causant des pertes de poids de tissu somatique ainsi que l’arrêt de la reproduction. Durant les expériences en laboratoire, les pétoncles ont montré une importante capacité à réguler leur respiration face à la diminution de la saturation en oxygène jusqu’à 24%. De manière surprenante, nous avons trouvé que cette espèce est capable de maintenir une filtration, quoique diminuée, même à des saturations en oxygène basses (5%). Sur la base des réponses physiologiques du pétoncle face à l’hypoxie et le rendement énergétique moindre du métabolisme anaérobie par rapport au métabolisme aérobie, nous faisons l’hypothèse d’une diminution de l’ensemble du métabolisme à des saturations en oxygène en dessous de la capacité de régulation de l’espèce. Des simulations d’un modèle incluant cette restriction énergétique (sur les flux d’assimilation et de mobilisation de la réserve) en conditions d’hypoxie parviennent à reproduire avec succès les observations de terrain effectuées dans la baie de Paracas : une plus grande exposition à l’hypoxie a pour conséquence une croissance réduite et un arrêt de la reproduction. Alors que le pétoncle possède des adaptations physiologique /métaboliques pour faire face à des conditions limitantes en oxygène, la croissance et la reproduction peuvent être compromises, affectant ainsi la productivité des cultures de cette espèce (cela en fonction de la fréquence, durée et intensité de l’hypoxie). Les résultats des observations, des expériences et des simulations réalisées lors de cette étude fournissent des informations utiles pour mieux gérer la culture de pétoncle péruvien. Sur la base de ces travaux, des estimations de capacité de charge des baies, et des évaluations de zones et profondeurs favorables pour la culture de ces pétoncles pourront être réalisées. / During the past two decades, the scallop (Argopecten Purpuratus) culture developed in the Peruvian coastal bays. The trophic availability linked to the upwelling system supports the production scallop. However, the Peruvian coasts are also known to have a high environmental variability especially in oceanic domain. Although scallop farms are vulnerable to production hazards (mortality, low growth), environmental variability in coastal bays of Peru and its effects on growth, reproduction and survival of this socially sensitive resource have been poorly studied. Paracas Bay in Pisco Peru is a traditional farming area where scallop highs and lows in productivity related to environmental conditions were recorded throughout its history. In order increase our knowledge on this issue, this study arises from three approaches : (1) observation in situ, (2) experimental physiology and (3) modelling of the energy budget of A. Purpuratus. An environmental monitoring conducted in the Paracas Bay shows that the oceanographic variability can be important, especially during the summer. Temperature variations of 8°C and oxic conditions ranging from supersaturation to anoxia (absence of oxygen) in the course of a day were observed. The high frequency monitoring has revealed a chronic, severe and prolonged hypoxic condition in Paracas Bay. Scallops grown on the bottom, where exposure to hypoxia was important (47% of the observed time) showed lower growth and reproductions conditions. However, during the summer, prolonged and severe hypoxic events affected both deep culture – scallops grown in suspension and on bottom- causing weight somatic tissue losses and cessation of reproduction. During the laboratory experiments, scallops showed significant ability to regulate their oxygen uptake face to decreased oxygen saturation up to 24%. Surprisingly, we found that this species is able to maintain filtration, although diminished, even at low oxygen saturations (5%). Based on the physiological responses of the Peruvian scallops face to hypoxia and the energy performance aerobic end anaerobic metabolism ; it is hypothesized that there exist a restriction in the energy flow available for metabolism at oxygen saturations below the regulation capacity of the organism. Model simulations including this energy restriction (on assimilation and reserves mobilization fluxes) against hypoxia can reproduce successfully field observations of Paracas Bay : greater exposure to hypoxia results in a reduced growth and reproductive conditions. Although the scallop has physiological adaptations/metabolism to deal with limited oxygen conditions, growth and reproduction can be compromised, affecting culture productivity of this species (according to the frequency, duration and intensity hypoxia). The results of observations, experiments and simulations obtained during this study provide useful information to better manage of Peruvian scallop cultures (ex. Load capacity estimates in the bays, evaluations of adequate areas/depths for culture, etc.).

Les estuaires, situés à l’interface entre les domaines continental et marin, constituent des zones essentielles dans les échanges de matières. Ils jouent dès lors un rôle capital pour les cycles biogéochimiques et biologiques et subissent, par ailleurs, des pressions climatiques et anthropiques croissantes depuis plusieurs décennies. Le présent travail a été focalisé sur les peuplements benthiques et pélagiques présents dans la partie fluviale (Garonne et Dordogne) de l’estuaire de la Gironde, zone àtrès faible salinité où ces peuplements n’avaient encore jamais été étudiés. Alors que la méiofaune, composée principalement de Nématodes, s’est avérée relativement abondante dans les domaines intertidal et subtidal, le macrobenthos est apparu composé essentiellement d’Oligochètes en intertidal et complètement absent en subtidal. La grande plasticité du copépode dominant Eurytemora affinis a été confirmée, celui-ci occupant une niche écologique différente dans la partie fluviale de l’estuaire par rapport à la zone haline. L’importance de la température plutôt que la qualité du pool nutritif sur la productivité d’E. affinis a été démontrée, mettant en évidence une fois de plus la grande adaptabilité de cette espèce dans un habitat très fluctuant. L’étude de l’habitat benthique et pélagique, notamment en terme de qualité du pool nutritif disponible pour les organismes, a démontré que la contribution de la matière organique réfractaire d’origine terrestre est dominante. La contribution du micro phytobenthos à la composition de la matière organique sédimentaire et pélagique a aussi été mise en évidence. Enfin,l’étude des communautés planctoniques dans la partie fluviale de l’estuaire de la Gironde a montré que l’espèce E. affinis y occupe une position clef. / Being at the interface between continental and marine systems, estuaries are essential areas for matter exchanges. Therefore, they play a crucial role in biological and biogeochemical cycles. In addition to natural fluctuations, these systems have also undergone increasing climate and anthropogenic pressures for several decades. The present work focused on the benthic and pelagic assemblages in the fluvial section (Garonne and Dordogne rivers) of the Gironde estuary, a low salinity area where these communities had never been studied. Meiofauna, mainly composed ofnematodes, was found in relatively high abundance in both intertidal and subtidal zones.Macrozoobenthos was essentially composed of oligochaetes in the intertidal, while it was totally absent in the subtidal areas. The high plasticity of the dominant copepod Eurytemora affinis was confirmed, with a different ecological niche in the freshwater section of the estuary compared to the haline area downstream. The importance of temperature rather than the quality of the nutrient pool on the productivity of E. affinis was demonstrated, thereby confirming the great adaptability of thisspecies to a highly fluctuating habitat. Study of benthic and pelagic habitat, especially in terms of quality of the nutrient pool available to the organisms, showed that the contribution of refractoryorganic matter with a terrestrial origin is dominant. A significant contribution of microphytobenthos to the composition of sedimentary and pelagic organic matter was also highlighted. Finally, the study of planktonic communities in the fluvial part of the Gironde estuary showed that the species E. affinis occupies a key position in this part of the estuary.

La dynamique d’une population résulte de la combinaison de plusieurs traits d’histoire de vie qui sont façonnés par l’histoire évolutive de cette population. L’altération d’un de ces traits par des contraintes environnementales peut donc avoir des effets sur la persistance de la population. Les ajustements individuels de certains traits phénotypiques pourraient permettre à cette population de répondre rapidement à ces contraintes sans la nécessité immédiate d’adaptations génétiques. Durant cette thèse, la variabilité de certains traits a été identifiée chez 3 espèces sentinelles des écosystèmes polaires. Ces résultats permettent de mieux comprendre les associations entre ces traits et les pressions évolutives qui en sont à l’origine, ainsi que l’importance de traits tels que la personnalité dans la part inexpliquée de la variabilité de la valeur sélective des individus. A terme, nous pourrions ainsi mieux évaluer la capacité d’adaptation des populations face aux changements globaux. / Population dynamics is driven by several life history traits shaped by the evolutionary history of the population. The alteration of one of these traits by environmental constraints may thus have effects on the population persistence. Individual adjustments of some phenotypic traits could then enable this population to rapidly respond to these constraints without the immediate necessity of genetic adaptations. During this PhD project, we identified variability in some of these traits in 3 sentinel species of polar ecosystems. These results allowed us to better understand the associations between these traits and the evolutionary pressures underlying these associations, as well as the importance of traits such as personality in the amount of variability in individuals’ fitness that remains unexplained. In the long term, we should then be able to better gauge the adaptive capacity of populations to face global changes.