No description available.

Understanding how migration, genetic drift, and natural selection interact to maintain the genetic and phenotypic variation we observe in natural populations is a central goal of population genetics. Amphibians provide excellent model organisms for investigating the interplay between these evolutionary forces because amphibians are generally characterized by limited dispersal abilities, high philopatry, and are obligately associated with the areas around suitable habitats (e.g. breeding ponds). Thus, on relatively small geographic scales, the relative effects of all of these evolutionary forces can be studied together. Here, we study the interaction of migration, genetic drift, natural selection, and historical process in the ornate chorus frog (Pseudacris ornata). We report the development and characterization of 10 polymorphic microsatellite genetic markers. Number of alleles per locus ranged from 2 to 21 averaging 9.2 and expected heterozygosities ranged from 0.10 to 0.97 averaging 0.52. However, in an analysis of two populations, three locus-by-population comparisons exhibited significant heterozygote deficiencies and indicated that null alleles may be present some loci. Furthermore, we characterized genetic structure and historical biogeographic patterns in P. ornata using these microsatellite markers along with mitochondrial DNA sequence data. Our data indicate that in these frogs, migration may play a large role in determining population structure as pairwise estimates of FST were relatively small ranging from 0.04 to 0.12 (global FST = 0.083). Additionally, we observed an overall pattern of isolation-by-distance in neutral genetic markers across the species range. Moreover, our data suggest that the Apalachicola River basin does not impede gene flow in P. ornata as it does in many vertebrate taxa. Interestingly, we identified significant genetic structure between populations separated by only 6 km. However, this fine scale genetic structure was only present in the more urbanized of two widespread sampling localities. Finally, in this study, we demonstrated that there was a significant correlation between the frequency of green frogs and latitude. There was a higher frequency of green frogs in southern samples and a lower frequency of green frogs in northern samples. However, when we interpreted this phenotypic cline in light of the overall pattern of isolation-by-distance, it was apparent that the neutral evolutionary forces of genetic drift and migration could explain the cline, and the invocation of natural selection was not necessary.

No description available.

Over the last 100 years sexual selection has advanced into a vast field of theoretical and empirical research. While Darwin’s idea of female preference being an integral mechanism of sexual selection is no longer debated, our understanding of female preference is still very limited. For example, we know little about the genetic variation in female preference, and the costs of preference over and above the costs of mating with particular male phenotypes. Additionally, while costs of mate choice are well documented, the benefits of mate choice and their implications are still debated. For example, controversy exists over the inevitability of good gene benefits and their capability to promote adaptive sexual selection. Furthermore, the adaptiveness of sexual selection itself is debated. Our understanding of the traits involved in mate choice is also far from complete. Here I investigated aspects of sexual selection in Drosophila simulans, employing a range of behavioural approaches along with artificial selection and environmental manipulations. The findings presented here indicate that female preference can evolve when directly selected on, and that preference itself is not particularly costly. There was also no conclusive evidence for the good genes benefits of mate choice in D. simulans. These benefits are considered crucial in promoting the adaptiveness of sexual selection, and although we found sexual selection to be adaptive under some test conditions it was not adaptive in other conditions. Our investigations into traits involved in mate choice established sex-specific genetic variation in cuticular hydrocarbons and the genetic architecture of this trait was found to sex-specific evolution of cuticular hydrocarbons under natural and sexual selection. Additionally, we found that a secondary sexual character, the sex combs was positively allometric – just like most signalling and weapon traits, and there was no association between trait fluctuating asymmetry and trait size. These findings collectively indicate that sexual selection in D. simulans is consistent with classical models of this process.

Les animaux font face à des changements environnementaux brutaux dus aux modifications de milieux liés à l'activité humaine et aux changements climatiques, et doivent s'ajuster rapidement à leur nouvel environnement. Certains processus cognitifs comme l'innovation et l'apprentissage permettent aux animaux d'intégrer de nouveaux comportements à leur répertoire comportemental (flexibilité comportementale), leur donnant l'opportunité d'intégrer un comportement plus optimal pour s'ajuster. Les performances cognitives varient entre espèces et les individus d'une même population et bien que des études récentes se soient intéressées aux causes des variations interindividuelles des performances cognitives, les conséquences restent peu explorées. Dans cette thèse, les questions des pressions de sélection s'exerçant sur les capacités cognitives sont abordées afin de mieux comprendre l'évolution de ces traits au sein d'une population naturelle de mésange charbonnière Parus major. Un nouveau test de résolution de problème a tout d'abord été présenté à des couples reproducteurs directement en milieu naturel. Les résultats ont montré que les couples les plus performants à résoudre la tâche surpassaient les couples les moins performants sur plusieurs mesures de succès reproducteur. Afin de vérifier que la motivation à nourrir les poussins ne biaisait pas cette relation, la taille de nichée a ensuite été manipulée, ce qui n'a pas affecté la performance subséquente des parents. Les couples innovateurs démontraient un meilleur succès reproducteur quel que soit le changement de la taille de nichée subit, ce qui suggère que cette performance influence bien le succès de reproduction, et non l'inverse. De plus, les couples innovateurs approvisionnaient leurs poussins plus souvent que les couples non innovateurs, suggérant que les innovateurs pourraient exploiter leur habitat de façon plus optimale. Dans un troisième temps, plusieurs caractéristiques morphologiques, dont la coloration des plumes, ont été reliées aux performances de résolution de problème et d'apprentissage. Ces liens, bien que complexes et condition-dépendants, pourraient indiquer un rôle de ces performances lors de la sélection sexuelle. Enfin, afin de tester l'effet du parasite sanguin du paludisme sur les traits comportementaux, un médicament contre le paludisme a été injecté à des femelles reproductrices. Cette injection n'a pas modifié leurs performances cognitives mais a augmenté leur niveau d'activité et d'exploration du nichoir en réponse à la tâche de résolution de problème. Ce parasite sanguin, très présent chez les populations depassereaux, pourrait donc expliquer les variations interindividuelles et interpopulationnelles de certains traits comportementaux en milieu naturel, au même titre que dans nombreux autres systèmes hôte-parasites étudiés. Les travaux présentés dans cette thèse ont permis de détailler pour la première fois la relation entre une performance cognitive et le succès reproducteur chez une population aviaire naturelle, une relation robuste et non influencée par la motivation à nourrir la couvée. Cette performance cognitive est reliée à plusieurs traits morphologiques, mais non à la charge parasitaire. Une meilleure exploitation de l'habitat et habileté à s'occuper des poussins pourrait expliquer cette relation. / Animals face a rapidly changing world due to anthropogenic habitat destruction and climate change, forcing them to quickly adjust their behaviour to new environmental conditions. Cognitive processes such as innovation and learning can allow animals to incorporate novel behaviours into their behavioural repertoires and facilitate optimal responses to environmental change. Cognitive performances vary between and within species and although several studies have recently addressed the causes of inter-individual variations in cognitive performance, the fitness consequences of this variation remain poorly explored in natural populations. In my PhD thesis, I investigated different selective pressures acting on innovation and learning performance to better understand the evolution of these traits in a natural population of great tits Parus major. Firstly, I designed a novel problem-solving task that involved opening a trap door to access chicks, and presented it to breeding great tit pairs in their natural habitat. I found that the most efficient birds at solving this task performed better at multiple measures of reproductive success than the less efficient. Secondly, to test whether chick provisioning motivation confounded this relationship, I manipulated brood size and recorded whether this affected the problem-solving performance of the parents. My results showed that this was not the case. Instead, solvers had higher reproductive success whatever the brood size manipulation experienced, supporting the hypothesis that this cognitive performance drives reproductive success rather than the opposite. Problem-solving performance correlates positively with reproductive success both at the early stages of breeding (i.e. number of eggs laid and hatched) and during the nestling rearing period (i.e. number and condition of fledged young). Moreover, solvers seem to provision their young at a higher rate than non-solvers, suggesting that solvers exploit their breeding habitat more efficiently than non-solvers. Thirdly, I found multiple links between morphological traits, among which feather colouration, and problem-solving and learning performances. Although complex and condition-dependent, these links suggest that cognitive performances may be under sexual selective pressures, since they can be signaled by morphological traits shown to be important in great tit mate choice. Finally, injecting breeding females with an anti-malaria drug did not affect their cognitive performances, but increased their level of activity and exploration when presented with the novel problem-solving task. This suggests that the presence of these blood parasites, which are frequent in passerine populations, could partly explain between-individual and between-population variation in certain behavioural traits in natural populations, as previously described in many other host-parasite study systems. In summary, my thesis provides the first detailed analysis of the relationship between cognitive performance and reproductive success in a wild bird population. My studies show that this relationship is robust and not confounded by parents’ motivation to provision their young. This problem-solving performance is also correlated with various morphological traits, but not with parasite load. The relationship between cognitive performance and reproductive success might be mediated through habitat exploitation and chick provisioning skills, but requires further investigation.

O palmiteiro (Euterpe edulis Mart.) é uma espécie nativa da Mata Atlântica cujas populações naturais encontram-se degradadas pelo extrativismo. Considerando a escassez de informações relativas às conseqüências genéticas da exploração de palmito, o objetivo deste estudo foi avaliar o impacto do processo de exploração sobre os níveis de diversidade, estrutura genética e tamanho efetivo de populações da espécie. Também foram estudados aspectos genéticos do recrutamento de plantas e o sistema reprodutivo da espécie. O estudo foi realizado em duas localidades do Estado de Santa Catarina, nos municípios de São Pedro de Alcântara e Ibirama. Em cada localidade foram escolhidas duas áreas de ocorrência natural de E. edulis, uma sem influência antrópica e outra que sofreu exploração de palmito, totalizando quatro populações. Os sistemas de exploração foram: (i) extrativismo - onde todos os indivíduos acima de 2 m de altura são cortados, incluindo plantas reprodutivas; and (ii) manejo - onde somente indivíduos acima de 9 cm de DAP são cortados, com a manutenção de 50 plantas reprodutivas por hectare. Em cada população foram examinadas plântulas, jovens e adultos, usando oito locos microssatélites e dez locos alozímicos. Os resultados revelaram que a espécie se reproduz por alogamia ( m tˆ = 0,996 para microssatélites e m tˆ = 1,000 para isoenzimas), porém a ocorrência de cruzamentos entre indivíduos aparentados (até 5%) e cruzamentos biparentais (10%) indica a ocorrência de cruzamentos não aleatórios. Em locos alozímicos, observaram-se as seguintes amplitudes de variação das estimativas de diversidade entre as categorias: Aˆ : 3,05 a 3,15; e Hˆ : 0,416 a 0,431; o Hˆ : 0,378 a 0,403. Em locos microssatélites, a variação observada foi a seguinte: Aˆ : 14,12 a 14,72; e Hˆ : 0,781 a 0,785; o Hˆ : 0,678 a 0,709. Nas populações não exploradas, houve um aumento na freqüência de heterozigotos na direção do estádio adulto, o que sugere a ação da seleção favorecendo o aumento de heterozigotos. Valores altos e significativos do índice de fixação ( fˆ ) foram observados, especialmente nos marcadores microssatélites, indicando desvios do equilíbrio de Hardy-Weinberg. De modo geral, ambos os marcadores revelaram um aumento dos valores de fˆ nas populações exploradas, especialmente entre as plântulas. As estimativas ST Gˆ e ST Rˆ não revelaram alterações na estrutura genética das populações exploradas e demostraram uma divergência genética inferior a 5% na maioria das comparações aos pares, em ambos os marcadores. O tamanho efetivo ( e Nˆ ) dos indivíduos adultos por hectare foi superior a 110 nas populações não pertubadas, enquanto nas populações exploradas, o tamanho efetivo por hectare foi reduzido para 45, sob manejo, e 14, sob extrativismo. Porém, o tamanho efetivo total das populações exploradas ainda é elevado, o que explica a manutenção dos altos níveis de diversidade nessas populações. Finalmente, a informação genética conjunta desses marcadores demonstrou que os efeitos da exploração foram pouco pronunciados até o momento em relação aos níveis de diversidade e estrutura genética das populações de E. edulis. Entretanto, a redução da população de cruzamentos resultou em alterações no comportamento reprodutivo dos indivíduos, promovendo um aumento nos níveis de endogamia nas coortes mais jovens das populações exploradas. Contudo, os resultados obtidos neste estudo indicaram questões adicionais a serem estudadas. Em função do elevado nível de variabilidade dos locos microssatélites observado em E. edulis, recomenda-se aumentar o tamanho das amostras visando otimizar a informação genética proporcionada por esses marcadores. Além disso, novos estudos são necessários sobre os efeitos do manejo tecnificado, uma vez que os resultados obtidos podem ter sido influenciados por outros eventos de exploração ocorridos no passado e pelas populações existentes nas proximidades devido ao elevado fluxo gênico da espécie. / Heart-of-palm tree (Euterpe edulis Mart.; Arecaceae) is a native species of the Atlantic forest whose natural populations are degraded by extractivism. Regarding the relative scarcity of information on the genetic consequences of palm heart exploitation, the aim of this study was to investigate the effects of two exploitation systems - extractivism and management - on the levels of variability, genetic structure and effective size of Euterpe edulis Mart. populations. We also investigated genetic aspects of the plant recruitment and the reproductive system of the species. Four natural populations of E. edulis with different histories of disturbance were surveyed in the districts of São Pedro de Alcântara and Ibirama, Santa Catarina, Brazil. At both sites, we sampled an undisturbed and an exploited population. The exploitation systems were: (i) extractivism - where most individuals higher than 2 m are harvested, including reproductive plants; and (ii) management - where only individuals with more than 9 cm of DBH are harvested, with the maintainance of 50 reproductive plants per ha. Three categories of plants, from seedlings to adults, were examined using eight microsatellite loci and ten allozyme loci. Results demonstrated the preferentially allogamic behaviour of the species ( m tˆ = 0.996 for microsatellites and m tˆ = 1.000 for allozymes), but the occurrence of matings among related individuals (5%) and biparental matings (10%) indicated the existence of non-random matings in this species. For allozymic loci, the following diversity estimates were obtained among the categories: Aˆ : 3.05 to 3.15; e Hˆ : 0.416 to 0.431; o Hˆ : 0.378 to 0.403. For microsatellites, the estimates were as follows: Aˆ : 14.12 to 14.72; e Hˆ : 0.781 to 0.785; o Hˆ : 0.678 to 0.709. In undisturbed populations, there was an increase in heterozygote frequency towards the adult stages, suggesting the action of natural selection favouring such heterozygote increase. Highly significant values of fixation index ( fˆ ) were observed, mainly at microsatellite loci, indicating departures from Hardy-Weinberg expectation. Both markers displayed an increase of fˆ values in the exploited populations, especially for seedlings. The estimates of interpopulation genetic variation ( ST Gˆ ; ST Rˆ ) revealed that more than 95% of the molecular genetic variability of the species is distributed within populations, and there was no evidence of changes in genetic structure of the exploited populations. Effective size ( e Nˆ ) per hectare of the adult individuals was higher than 110 in the two undisturbed populations, while in the exploited populations the effective size per hectare was reduced to 45 under management, and 14 under extractivism. However, the total effective size of the exploited populations was still high, which explains the maintenance of high diversity levels in these populations. Finally, the genetic information from both markers displayed small pronounced effects of the exploitation process on variability and population genetic structure of E. edulis, with the exception of an increase in the inbreeding levels among seedlings and juveniles of the exploited populations. However, our results raised further questions for study. Because of the hypervariability of microssatellite loci used in this work, we would recommend an increase in the sample size (>100) in order to optimize the genetic information provided by these markers. Moreover, new investigations are necessary on the effects of management, since the results from this study could have been influenced by other exploitation events that have occurred in the past and by the existence, due to the high gene flow of the species, of surrounding undisturbed populations.

Mon travail de thèse est fondé sur la recherche d’une meilleure compréhension de la distribution géographique des polymorphismes érythrocytaires: antigènes de surface des systèmes de groupes sanguins érythrocytaires (GSE) et glucose-6-phosphate déshydrogénase (G6PD) intracellulaire. L’analyse sur 75 populations d’Asie des fréquences de l'allèle DI*01 du système de GSE Diego, des haplotypes C2-M217 et C2-M401 du chromosome Y, des coordonnées géographiques et des langues, a pu montrer la corrélation entre ces marqueurs. La répartition de DI*01 semble suivre les conquêtes mongoles, avec une expansion radiale depuis la Mongolie, porté par les nomades de langue Altaïque présentant C2-M217 et C2-M401. L'étude du gène G6PD chez 80 individus de Guyane Française de la communauté des Noirs Marrons originaire d’Afrique sub-Saharienne, aborde les relations santé-environnement. Les mutations du déficit en G6PD caractéristiques des variants sub-Sahariens ont été retrouvées chez une personne sur huit. La répartition du déficit était inconnue en Guyane Française et est encore mal connue en Amérique Latine et dans les Caraïbes, où sévit encore Plasmodium vivax dont le traitement nécessite l’utilisation de la primaquine pouvant entraîner une hémolyse sévère chez les individus G6PD-déficients. Mon troisième objectif a été de mettre en évidence l’influence de différents facteurs sur la répartition des polymorphismes de 10 systèmes de GSE étudiant 343 populations. Par des modélisations, les fréquences alléliques ont été confrontées aux données environnementales et culturelles. Enfin, une étude a été réalisée sur le système Duffy avec des analyses de détection de la sélection sur données SNP. / My Ph.D. work is based on the search for a better understanding of the geographical distribution of red blood cell polymorphisms: the surface antigens of red cell blood group systems (BGS) and the intracellular glucose 6-phosphate dehydrogenase (G6PD). The analysis on 75 Eurasian populations of frequencies of the DI*01 allele coding for Diego a antigen of Diego BGS, the C2-M217 and C2-M401 haplotypes of the Y chromosome, geographic coordinates and languages, has shown a correlation between these markers. The DI*01 distribution seems to follow the Mongol conquests, carried by the Altaic-speaking nomads possessing the C2-M217 and C2-M401 haplotypes with a radial expansion from Mongolia. The study of the G6PD gene in 80 individuals from French Guiana of the Noir Marron community originating from sub-Saharan Africa, addresses health-environment relations. Characteristic mutations of sub-Saharan variants of G6PD deficiency have occurred in one in eight people. The G6PD deficiency distribution was previously unknown in French Guiana and is still poorly known in Latin America and the Caribbean, where Plasmodium vivax still cracks down. Its treatment requires the use of primaquine which may cause severe haemolysis in G6PD-deficient individuals. My third objective was to highlight the influence of different factors on the distribution of polymorphisms of 10 BGS studying 343 populations. Through model adjustments, allelic frequencies have been confronted to environmental and cultural data. Finally, a study has been also conducted on the Duffy BGS by analyses of detection of natural selection on SNP data.

Made available in DSpace on 2016-04-28T14:16:36Z (GMT). No. of bitstreams: 1 Enezio Eugenio de Almeida Filho.pdf: 4288341 bytes, checksum: 6d7c3e5e0f23728ac321058b96f617c8 (MD5) Previous issue date: 2008-10-17 / Discovery Institute - Center for Science and Culture / This research follows the line of History and Theory of Science that has as a goal to explain the construction of scientific thought by discussing the foundation of hypotheses and theories within their historical contexts. The goal of this thesis is to analyze Mivart´s critiques and Darwin´s answers, and to verify if they were scientifically well formulated and based considering the scientific context of that time. The reason for writing this work is an attempt to fill a gap in the History of Science about the scientific controversy between Mivart and Darwin on the role of natural selection in the origin of species. This work´s hypotheses are two: that Mivart´s critiques, despite being religiously motivated, were plausible scientifically, and that Darwin answered them fully. This research analyzes the primary sources of Mivart (Genesis of species) and Darwin's Origin of Species, and other secondary sources. The result reached was that Mivart´s critiques were indeed scientific, and that Darwin answered them according to the evidences and scientific knowledge then available / Esta pesquisa segue a linha de História e Teoria da Ciência que objetiva trazer esclarecimentos sobre a construção do pensamento científico através da discussão da fundamentação de hipóteses e teorias dentro do seu contexto histórico. O objetivo desta dissertação é analisar as críticas de Mivart e as respostas dadas por Darwin, e verificar se elas estavam bem formuladas e fundamentadas cientificamente considerando-se o contexto científico daquela época. A justificativa para a realização desta trabalho é tentar preencher uma lacuna em História da Ciência sobre a controvérsia científica entre Mivart e Darwin sobre o papel da seleção natural na origem das espécies. As hipóteses deste trabalho são duas: as críticas de Mivart, apesar de terem sido religiosamente fundamentadas, eram cientificamente plausíveis, e Darwin as respondeu satisfatoriamente. O aspecto teórico-metodológico foi a análise das fontes primárias de Mivart (Genesis of species) e de Darwin (Origin of species), e outras fontes secundárias. O resultado obtido foi que as críticas de Mivart eram científicas, e que Darwin respondeu-as conforme as evidências e o conhecimento científico da época

Le processus sélectif est-il nié, persistant ou dialectiquement réalisé dans la civilisation ? De ce problème, deux thèses générales se dégagent : (1) celle de l’épuisement de la sélection naturelle, la société humaine témoignant d’une véritable émancipation vitale et (2) celle d’un report des pressions de sélection, le système de contraintes sélectives demeurant effectif. En fait, cette interrogation se trouve esquissée dès l’« anthropologie » de Charles Darwin (1871), sujette encore à débats, notamment sur l’existence du darwinisme social de ce dernier, forme, justement, de report des pressions de sélection. Face à la thèse de l’incohérence doctrinale de cette « anthropologie », qui légitime malgré elle qu’on fasse tout dire de Darwin, on proposera une cohérence articulée autour du concept de sympathie et des effets combinés de la sélection, de la culture et de l’habitude. Ensuite, il s’agira de proposer une théorie de l’émancipation vitale, mêlant report des pressions de sélection et émancipation par procès ‘technosymbiotique’, néologisme au lien fort avec la cultural niche construction (Odling-Smee). Prendre la civilisation comme une niche écologique, la culture comme un paramètre, résoudra une bonne part des problèmes théoriques et de ce dualisme identitaire qu’on retrouve si souvent dans notre approche de l’homme et de sa société. La réflexion sur la civilisation nous conduira à nous interroger sur le biotope économique, comme marque essentielle et originale de notre niche écologique. Notre émancipation biologique côtoie ainsi le maintien du système de contrainte sélectionniste, dans un biotope, dès lors, de plus en plus biomimétique / Is the selective process irrelevant, does it persist, or is it dialectically achieved in civilization? Two general theses arise from this question: (1) either the progressive extinction of natural selection, human society thus witnessing a genuine vital emancipation or (2) the persistence of selection pressures, the system of selective constraints thus remaining effective. In fact, this question was outlined in 1871 with Charles Darwin’s “anthropology”; his anthropology and notably his social Darwinism, a form of displacement of selection pressures continue to be debated today. Confronted with the thesis of the doctrinal inconsistency of this “anthropology” which allows Darwin’s words to be interpreted at will, we shall put forward a form of coherence based on the concept of sympathy and the combined effects of selection, culture and habits. We shall then put forward a theory of vital emancipation that combines the persistence of selection pressures and emancipation via a technosymbiotic process, a neologism similar to cultural niche construction (Odling-Smee). Considering civilization as an ecological niche and culture as a parameter will solve most theoretical problems, notably related to the identity dualism associated with a conventional approach to man and society. Our reflection on civilization will lead us to focus on and investigate into the economic biotope understood as an essential and specific feature of our ecological niche. Following this approach, man’s biological emancipation coexists with a system of selectionist constraint in a biotope that is, as a consequence, increasingly biomimetic

Les associations symbiotiques entre microorganismes et eucaryotes sont omniprésentes dans le monde vivant. Ces microorganismes peuvent jouer un rôle crucial dans l’évolution et l’écologie de leurs porteurs en modifiant leur phénotype. Ces symbiotes étant le plus souvent héritables, les phénotypes étendus résultant de ces associations symbiotiques peuvent se transmettre aux générations suivantes. Certains microorganismes vont permettre l’accès à une ressource alimentaire, d’autres conférer une protection contre un ennemi. Une telle protection symbiotique est rencontrée chez le puceron du pois (Acyrthosiphon pisum) en interaction avec la bactérie Hamiltonella defensa. Cette symbiose confère au puceron une résistance face à l’attaque de son principal ennemi : le parasitoïde Aphidius ervi. Les populations de ce ravageur des Légumineuses sont structurées en biotypes (populations spécialisées sur des plantes hôtes). La distribution du symbiote protecteur au sein des populations de pucerons est singulière. De nombreux individus vivant sur la luzerne, la bugrane ou les genêts abritent ce symbiote alors qu’il est peu fréquent dans les populations d’autres biotypes d’A. pisum comme le pois ou le trèfle. Nous avons cherché à comprendre pourquoi H. defensa n’était pas retrouvé chez tous les biotypes du puceron du pois. Afin de prédire la dynamique de la symbiose protectrice et le potentiel de résistance dans les populations aphidiennes naturelles, nous nous sommes intéressés à plusieurs processus écologiques et évolutifs. L’incidence de la pression des parasitoïdes sur la composition des populations symbiotiques a été mesurée chez trois biotypes (luzerne, pois et trèfle) à travers une approche terrain. La distribution du symbiote H. defensa dans les populations est directement dépendante de la variabilité du phénotype associé exprimé dans les différentes populations, j’ai identifié les phénotypes associés au symbiote pour des pucerons issus de différents biotypes ainsi que l’influence du contexte local sur ces phénotypes. L’absence d’H. defensa chez certains individus peut s’expliquer par la redondance d’une fonction protectrice en place chez ces biotypes comme un alternative symbiotique autre que H. defensa ou encore une immunité forte. Enfin, nous avons testé si le cumule des protections symbiotiques conférées par deux bactéries du cortège du puceron du pois pouvaient se cumuler créant ainsi des super-organismes. Mon travail met en évidence l’implication de nombreux facteurs dans la prédiction des fréquences symbiotiques d’une bactérie facultative dans les populations d’hôte. / Symbiotic associations between microorganisms and eukaryotes are ubiquitous in the living world. These microorganisms can play a crucial role in the evolution and ecology of their hosts by altering their phenotypes. Since these symbionts are usually heritable, extended phenotypes resulting from these symbiotic associations may be transmitted to subsequent generations. Some microorganisms will allow access to a food source; others will provide protection against natural enemies. Such symbiotic protection is found in the pea aphid (Acyrthosiphon pisum) in its interaction with the bacteria Hamiltonella defensa. This symbiosis provides the aphid with a resistance against the attack of its main parasitoid enemy: Aphidius ervi. The populations of the pea aphid, a legume pest insect, are structured in different biotypes (specialized populations on host plants). The distribution of this protective symbiont within pea aphid populations is singular: many individuals living on Medicago sativa (alfalfa), Ononis spinosa or Genista sagittalis and G. tinctoria host plant with H. defensa while it is rarely found in other populations of A. pisum biotypes such as Pisum sativum (pea) or Trifolium sp. (clover). We sought to understand why H. defensa was not found in every pea aphid biotype. In order to predict the dynamics of the protective symbiosis and the resistance potential in natural aphid populations, we focused on several ecological and evolutionary processes. We measured the consequence of parasitoid stress in the composition of symbiotic populations in three different biotypes (alfalfa, clover and pea) using a field approach. The distribution of H. defensa symbiont in populations dependent directly on the variability of the associated phenotype expressed in different populations. We identified the phenotypes associated with this symbiont in aphids from different biotypes, and the influence of the local context on these phenotypes. The lack of H. defensa in some individuals can be explained by the redundancy of a protective function already in place in these biotypes, such as an alternative symbiotic species or a strong immunity. Finally, we tested whether the symbiotic protections provided by two different bacteria in the pea aphid could be cumulated, thus creating super-organisms. My work highlights the many factors involved in predicting the frequencies of facultative symbiotic bacteria in host populations.