Made available in DSpace on 2014-07-29T16:21:16Z (GMT). No. of bitstreams: 1 dissertacao Poliana Mendes.pdf: 900873 bytes, checksum: 549aa0a8671a1a0cdfa3dc72f555ddc7 (MD5) Previous issue date: 2011-03-04 / The species loss in recent decades can be comparable to a mass extinction event. This scenario emphasizes the need for biodiversity conservation before it disappears, but the resources devoted to this purpose are limited. In this context, identifying species that possess characteristics that predispose them to a greater sensitivity to environmental changes may help understanding how species losses occur. In addition, proposals for conservation strategies from existing knowledge about species are practical ways of minimizing the loss of biodiversity. The greater ecological diversity of the order Chiroptera, when compared with other groups of mammals, suggests that this may be a good study group to research in conservation biology. In this scenario, Chapter 1 uses a scoring methodology that considered four parameters to define priorities for conservation of bats: risk of extinction, endemism, originality and the public interest. Later, we checked if priority species and areas are covered by any protected areas. It was also verified if priority areas for bats are more congruent with global priorities, focused on pro-active or reactive strategies. The three species with the highest score for conservation priority were Acerodon humilis, Acerodon jubatus and Latidens salimali. The priority areas for bat conservation are in South Amercia, Madagascar, some spots in Africa, Australia, New Zealand and Indonesian Islands. The sites covered by reactive strategies have greater priority level for conservation of bats, but we observed both reactive and pro-active strategies, within priority boxes. Only one quarter of the priority squares for bats have 10% or more of conserved areas within I-IV criteria, idealized values for 2010 Conservation Biodiversity (CBD). The results suggest that tropical areas, which also have more species of bats, are the ones that require more attention from conservation programs and much of these areas are minimally represented by conservation units, emphasizing the importance of investments for biodiversity conservation in these locations. Both reactive and pro-active strategies are important for biodiversity maintenance of bats, despite the reactive strategies being more representative in grid cells with the highest values of priority. In chapter 2, we checked if there is a relationship between bats biological features and extinction risk. Features used were: body mass, litter size, forearm size, wing length, gestational length and age of sexual maturity. Since the relationship between these features and the risk of extinction may be biased by phylogenetic relationships, we used a Phylogenetic Eigenvectors regression analysis (PVR) to remove the phylogenetic components of predictors. All variables addressed except gestational length are phylogenetically structured. Body mass, forearm length, wing length and litter size are related to the extinction risk. Since higher residual values for body mass and forearm size are associated with extinction risk and lower residual values for wing length and litter size are more related to the extinction risk. Smaller wing length as predictor of extinction risk may be associated with the species largest mobility capacity with larger wings. Body mass is a commonly associated feature with extinction risk, and this relationship can be explained by the relationship of this variable with slow life history features, higher species threat due to hunting, greater environmental resource acquisition or larger life area. Despite the small body size in mammals is associated with the lower extinction risk, bats unlike most small mammals have a slow life history, a factor that increases the susceptibility to species extinction. / A perda de espécies das últimas décadas é equiparável a um evento de extinção em massa. Esse cenário enfatiza a necessidade da conservação da biodiversidade antes que ela desapareça, porém os recursos destinados a esse propósito são limitados. Sob esse contexto, identificar espécies que possuem características que as predispõe a uma maior sensibilidade a alterações ambientais pode auxiliar no entendimento de como ocorre a perda de espécies. Além disso, propostas de estratégias de conservação, a partir do conhecimento já existente sobre as espécies, são maneiras práticas de tentar minimizar a perda da biodiversidade. A grande diversidade ecológica da ordem Chiroptera, quando comparada com outros grupos de mamíferos, sugere que este pode ser um bom grupo de estudo para a pesquisa em biologia da conservação. Diante deste cenário, no Capítulo 1 utilizamos uma metodologia de pontuação que considerou quatro parâmetros para definir prioridades de conservação para morcegos: risco de extinção, endemismo, originalidade e interesse público. Posteriormente, verificamos se áreas e espécies prioritárias são cobertas por alguma área protegida. Foi também verificado se as áreas prioritárias para morcegos são mais congruentes com prioridades globais, focadas em estratégias proativas ou reativas. As três espécies com maior pontuação de prioridade de conservação foram Acerodon humilis, Acerodon jubatus e Latidens salimali. As áreas prioritárias para a conservação de morcegos estão na América do Sul, Madagascar, alguns locais na África, Austrália, Nova Zelândia e Ilhas da Indonésia. Os locais cobertos por estratégias reativas possuem maior valor de prioridade de conservação para morcegos, porém observamos tanto estratégias proativas quanto reativas, dentre as quadrículas prioritárias. Somente um quarto das quadrículas prioritárias para morcegos possuem 10% ou mais de áreas preservadas dentro dos critérios de I a IV, valor idealizado para 2010 na Convenção da Biodiversidade (CBD). Os resultados obtidos sugerem que as áreas tropicais, onde também existem mais espécies de morcegos, são as que necessitam mais atenção dos programas de conservação e grande parte destas áreas ainda não estão minimamente representadas por unidades de conservação, enfatizando a importância de investimentos para a conservação da biodiversidade nesses locais. Tanto estratégias de conservação reativas como proativas são importantes para manter a biodiversidade prioritária de morcegos, apesar das estratégias reativas serem mais representativas nas quadrículas com os maiores valores de prioridade. No Capítulo 2 verificamos se há relação entre características biológicas dos morcegos e o risco de extinção. As características utilizadas foram: massa corporal, tamanho da ninhada, tamanho do antebraço, comprimento da asa, duração da gestação e idade da maturidade sexual. Como a relação entre essas características e o risco de extinção pode estar enviesada pelas relações filogenéticas, utilizamos uma Análise de Regressão por Autovetores Filogenéticos (PVR) para retirar o componente filogenético das variáveis preditoras. Todas as variáveis abordadas, exceto duração da gestação estão estruturadas filogeneticamente. Massa corporal, tamanho do antebraço, comprimento da asa e tamanho da ninhada estão relacionados com o risco de extinção. Sendo que maiores valores residuais para massa corporal e tamanho do antebraço estão relacionados com o risco de extinção e menores valores residuais para comprimento da asa e tamanho da ninhada estão mais relacionados com o risco de extinção. Menores comprimentos da asa como preditor do risco de extinção pode estar associado com a maior capacidade de locomoção de espécies com maiores asas. A massa corporal é uma característica comumente associada com o risco de extinção, e essa relação pode ser explicada através da relação desta variável com características relacionadas a uma história de vida lenta, maior ameaça das espécies maiores devido a caça, maior aquisição de recursos do ambiente ou maior área de vida. Apesar do pequeno tamanho corporal em mamíferos ser associado com menor risco de extinção, os morcegos ao contrário da maioria dos mamíferos de pequeno porte, possuem história de vida lenta, fator que aumenta a predisposição de espécies à extinção. Os resultados deste estudo mostram que é possível utilizar características intrínsecas das espécies para predizer o risco de extinção, e isso pode ser útil para estabelecer estratégias de conservação para espécies classificadas como Deficientes de Dados, pois devido a suas características elas podem ser aproximadas das espécies ameaçadas ou não ameaçadas. Além disso, é possível propor estratégias para estabelecer prioridades de conservação de forma simples através da metodologia de pontuação, apesar da arbitrariedade dessa metodologia ao definir as pontuações para cada parâmetro.

Life history traits affect the timing and pattern of maturation, reproduction, and survival during an organism’s lifecycle and are the major components influencing Darwinian fitness. Co-evolved patterns of these traits are known as life history strategies (LHS) and variation occurs between individuals, populations, and species. The polymorphisms underlying LHS are important targets of natural selection, yet the underlying genes and physiological mechanisms remain largely unknown. Mapping the genetic basis of a LHS and subsequently unraveling the associated physiological mechanisms is a challenging task, as complex phenotypes are often polygenic. However, in several systems discrete LHS are maintained within the population and are inherited as a single locus with pleiotropic effects. These systems provide a promising starting point for investigation into LHS mechanisms and this thesis focuses on one such strategy - the Alba polymorphism in Colias butterflies. Alba is inherited as a single autosomal locus, expressed only in females, and simultaneously affects development rate, reproductive potential, and wing color. Alba females are white, while the alternative morph is yellow/orange. About 28 of 90 species exhibit polymorphic females, though whether the Alba mechanism and associated tradeoffs are conserved across the genus remains to be determined. In this thesis I primarily focus on the species Colias croceus and integrate results from lipidomics, transcriptomics, microscopy, and genomics to gain insights to the proximate mechanisms underlying Alba and Alba’s evolution within the genus. Lipidomics confirm that, consistent with findings in New World species, C. croceus Alba females have larger abdominal lipid stores than orange, an advantage which is temperature dependent and arises primarily due to mobilized lipids. Gene expression data suggests differences in resource allocation, with Alba females investing in reproduction rather than wing color, consistent with previous findings in other Colias species. Additionally, I identify a morphological basis for Alba’s white wing color. Alba females from C. croceus, an Old World species, and Colias eurytheme, a New World species both exhibit a significant reduction in pigment granules, the structures within the wing scale that contain pigment. This is a trait that seems to be unique to Colias as other white Pierid butterflies have an abundance of pigment granules, similar to orange females. I also map the genetic basis of Alba to a single genomic region containing an Alba specific, Jockey-like transposable element insertion. Interestingly this transposable element​ is located downstream of BarH-1, a gene known to affect pigment granule formation in Drosophila. Finally, I construct a phylogeny using a global distribution of 20 Colias species to facilitate investigations of Alba’s evolution within the genus. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.</p>

In this study, we tested the long-term and negative effects of microcystin-producing cyanobacterium Microcystis aeruginosa from Vietnam on Daphnia magna under the laboratory conditions. The test organisms were fed with mixtures of green alga Scenedesmus armatus. and toxic M. aeruginosa at different ratios (10% Microcystis + 90% Scenedesmus, 50% Microcystis + 50% Scenedesmus, 100% Microcystis, and 100% Scenedesmus) for over a period of 21 days. The life history traits of the organisms such as, survival, maturation, fecundity were daily recorded. Besides, the intrinsic population rate of D. magna in each treatment was also calculated based on the survivorship, the reproductive age and the clutch size of the animals. The results showed that survival, maturation and reproduction of the D. magna fed with 10, 50 and 100% M. aeruginosa was impaired. Additionally, the intrinsic population rate of the exposed D. magna was lower than that of the control. This study evidenced the adverse effects of toxic M. aeruginosa on both the individual and intrinsic population levels of D. magna. To our knowledge, this is the first report on the chronically detrimental impacts of toxic M. aeruginosa isolated from Vietnam on D. magna and contributed the scientific information on the severe influences of toxic cyanobacteria world wide. / Trong bài viết này, chúng tôi nghiên cứu ảnh hưởng xấu mãn tính của loài vi khuẩn lam Microcystis aeruginosa có khả năng sản sinh độc tố microcysin từ Việt Nam lên Daphnia magna trong điều kiện phòng thí nghiệm. Sinh vật thí nghiệm được cho ăn với hỗn hợp tảo lục Scenedesmus armatus và M. aeruginosa có độc ở các tỷ lệ khác nhau (10% Microcystis + 90% Scenedesmus, 50% Microcystis + 50% Scenedesmus, 100% Microcystis, và 100% Scenedesmus) trong thời gian 21 ngày. Các đặc điểm vòng đời của sinh vật bao gồm sức sống, sự thành thục, sức sinh sản được theo dõi hàng ngày. Bên cạnh đó, tỷ lệ phát triển quần thể của D. magna trong từng lô thí nghiệm cũng được tính toán dựa vào sức sống, tuổi sinh sản và kích cỡ sinh sản của sinh vật. Kết quả cho thấy, sức sống, tuổi thành thục và sự sinh sản của D. magna cho ăn với 10, 50 và 100% M. aeruginosa bị ảnh hưởng xấu. Bên cạnh đó, tỷ lệ phát triển quần thể của D. magna trong lô phơi nhiễm thấp hơn so với đối chứng. Nghiên cứu này chứng minh ảnh hưởng xấu của M. aeruginosa có độc lên cả hai mức độ cá thể và quần thể của D. magna. Theo hiểu biết của chúng tôi, đây là báo cáo đầu tiên về ảnh hưởng xấu mãn tính của M. aeruginosa có độc phân lập từ Việt Nam lên D. magna and đóng góp thêm thông tin khoa học cho những ảnh hưởng nghiêm trọng của vi khuẩn lam có độc trên khắp thế giới.

Dans l'environnement, les organismes sont soumis à des stress de multiples natures (e.g., polluants et pathogènes/parasites). Dans ce contexte, le système immunitaire joue un rôle fondamental. La pression chimique exercée par les polluants peut impacter leur système immunitaire, affaiblir leur santé et les prédisposer à contracter des maladies infectieuses. En écotoxicologie, l'évaluation de marqueurs d'immunocompétence peut servir à diagnostiquer l'état de santé des organismes et mieux comprendre le danger immunotoxique des xénobiotiques. Lymnaea stagnalis est un gastéropode d'eau douce représentatif de nombreux milieux lentiques sur la planète. Des tests OCDE de reprotoxicité sont disponibles mais peu d'études se sont focalisées sur des paramètres immunotoxiques. Le premier axe de la thèse se porte sur la connaissance et le développement de méthodes pour évaluer l'immunocompétence de manière répétée à l'échelle individuelle chez L. stagnalis. Le deuxième axe évalue cette approche multibiomarqueurs dans différents contextes écotoxicologiques. Plusieurs populations (élevages vs terrain), temps d'expositions (3 vs 29 – 44 jours), concentrations d'exposition (environnementales vs non réalistes) et contaminants ont été évalués : des médicaments (les anti-cancéreux Etoposide et cyclophosphamide, l'anti-rejet de greffes cyclosporine A et l'antiinflammatoire diclofenac), l'insecticide deltaméthrine, le métal cadmium et des effluents de station d'épuration. Des comparaisons entre des traits de vie et des traits immunitaires ont été réalisées. La réflexion est bâtie sur les questionnements relatifs à (i) la sensibilité de l'approche, (ii) le temps de réponse des marqueurs, (iii) leur précocité physiologique, (iv) la transposition d'immunotoxicité de xénobiotiques entre le phylum des chordata et L. stagnalis et (vi) l'utilisation pratique de L. stagnalis (élevages, collecte en milieu naturel, calibration, reproduction) / In natural environments, animals encounter multiple stresses (e.g., pollutants and pathogens/ parasites). In this context, the immune system plays a pivotal role. Chemical insults from pollutants can jeopardize the immune system of these animals, weaken their health and make them vulnerable to contracting infectious diseases. In ecotoxicology, assessment of immunocompetence markers can be used to diagnose the health of organisms and better understand the immunotoxic hazard of xenobiotics. Lymnaea stagnalis is a freshwater gastropod representative of several lentic ecosystems on the planet. OECD reprotoxicity tests are available using this species, but too few studies have focused on immunotoxic parameters. The first part of this thesis covers the description, comprehension and development of the methods used to assess the immunocompetence at an individual scale and repeatedly within an experiment in L. stagnalis. The second part assesses this multibiomarker approach in several ecotoxicological contexts. Several populations (laboratory-bred vs collected in the field), time exposures (3 vs 29–44 days), concentrations (environmental vs unrealistic) and contaminants were evaluated : pharmaceuticals (the anti-cancer drugs etoposide and cyclophosphamide, the anti-xenograft rejection drug cyclosporine A, the anti-inflammatory drug diclofenac), the insecticide deltamethrin, the metal cadmium and wastewater treatment plant effluents. The general reasoning is built on questions relative to (i) the sensitivity of the approach, (ii) the rapidity of the response, (iii) their physiological precocity of alteration (immune vs life-history traits), (iv) the transposition of xenobiotic immunotoxicity between L. stagnalis and the Chordata phylum and (vi) the pragmatic use of L. stagnalis (breeding, collection in the environment, calibration and reproduction)

Cette thèse porte un regard évolutif sur les invasions biologiques qui sont une menace écologique, économique et sanitaire grandissante.Qu'ils en soient la cause ou la conséquence, les invasions sont en effet le théâtre de changements évolutifs rapides et importants.Ces changements peuvent être liés à une différence de pression de sélection entre l'aire d'origine et l'aire envahie, mais peuvent aussi être initiés par des évènements démo-génétiques comme un goulot d'étranglement démographique ou l'admixture (hybridation intra-spécifique) entre populations génétiquement différentes.Les changements évolutifs concernent aussi bien des traits d'histoire de vie liés à la reproduction que le fardeau génétique et la dépression de consanguinité.La forte dérive génétique qui peut se produire au cours d'un goulot d'étranglement peut conduire à la purge ou la fixation rapide d'allèles délétères responsables du fardeau génétique.Les trais de reproduction peuvent eux aussi influencer directement l'issue d'une invasion, au travers du taux d'accroissement démographique de la population.Ils peuvent aussi avoir un effet indirect sur le succès d'introduction en modifiant l'intensité des effets des évènements démo-génétiques.Au cours de cette thèse, j'ai étudié l'évolution du fardeau génétique et de traits de reproduction au cours d'une invasion biologique grâce à (i) une série d'expériences sur l'espèce envahissante modèle Harmonia axyridis (la coccinelle asiatique) et à (ii) un modèle théorique de dynamique de la fréquence d'un allèle délétère dans une population subissant un goulot d'étranglement.Mes résultats montrent que les populations envahissantes ont des traits de reproduction plus performants que celles de l'aire native.En particulier, les femelles envahissantes présentent une fécondité plus élevée et fécondent leurs œufs avec le sperme d'un plus grand nombre de mâles.Il n'existe pas, chez cette espèce, de mécanisme évident d'évitement de la consanguinité, bien que les populations de l'aire native souffrent de dépression de consanguinité contrairement à celles de l'aire envahie.La dépression de consanguinité peut évoluer très vite chez cette espèce en cas de fort goulot d'étranglement.Dans les conditions expérimentales, les allèles délétères étaient parfois purgés, mais ont souvent été fixés dans la population au cours d'un goulot.Enfin, le modèle théorique a montré que les probabilités de perte ou de fixation d'un allèle délétère récessif peuvent toutes deux augmenter rapidement par dérive au cours d'un goulot d'étranglement d'intensité modérée.Ces résultats soulignent l'importance du hasard sur le succès d'une invasion biologique.Puisque la probabilité d'émergence de combinaisons génomiques favorables à l'invasion augmente avec le nombre d'introduction, limiter le nombre d'évènements d'introduction peut s'avérer déterminant pour prévenir de futures invasions biologiques. / This thesis provides some evolutionary insights on biological invasions, which represent a growing threat on ecology, economy and public health.Biological invasions are a place of rapid and important evolutionary changes that can be the cause or the consequence of invasion success.These changes can be caused by differences in selective pressures between the native and the invaded area.They can also be due to demo-genetic events such as demographic bottlenecks and admixture (emph{i.e.} intra-specific hybridisation) between genetically distinct populations.Evolutionary changes affect life-history traits (including reproductive traits) as well as the genetic load and inbreeding depression.Genetic drift can be strong during a bottleneck and can induce the rapid purging or fixation of deleterious alleles responsible for the genetic load.Reproductive traits can also influence the fate of an invasion by changing the demographic growth rate.Moreover, they can have an indirect impact on the success of introduction by altering the intensity of demo-genetic events.Throughout this thesis, I studied the evolution of the genetic load and of reproductive traits by the mean of (i) laboratory experiments using the invasive Harlequin ladybird Harmonia axyridis as a model species and (ii) through the study of a theoretical model of the dynamics of allele frequencies during a bottleneck.My results show that invasive populations have better reproductive traits than those from the native area.Particularily, invasive females display an increased fecundity and fertilize their eggs with the sperm of a higher number of males.In this species, there is no obvious mechanism of inbreeding avoidance, even though native populations suffer to inbreeding depression contrarily to invasive ones.Inbreeding depression can evolve quickly in this species if the population goes through a severe bottleneck.In my experiments, deleterious alleles were often fixed in the population during the bottleneck, but were sometimes purged.Finally, the theoretical model studied described show that the probability of complete loss or fixation of a deleterious recessive allele can both increase by drift during a bottleneck.These results highlight the importance of chance on the success of a biological invasion.Because the probability of emergence of genomic combinations that can favour an invasion increases with the number of introduction events, limiting the number of introduction events might be an efficient way to prevent or minimise upcoming biological invasions.

Trade-off between offspring size and number belongs to the most discussed concepts in the life history theory. The aim of this study was to elucidate the relationship between egg size, clutch size and female body mass at the family level in bird's and to examine whether there is the relationship between offspring size and number and life history traits specific for particular bird families. From published sources, I collected data about 5.073 species belong in 146 families. Most species of birds lay smaller clutches, on average three eggs. In 112 families from 130 tested eggs size was positively correlated with female body mass. There is evidence that egg size and clutch size are inversely related in 83 families from 130 tested but only for 34 families was significant. The relationship exists independently of female body mass across bird families and this suggests a trade-off between these traits. The relationship between the strength and shape of egg size-number correlations and life history characteristics of bird families was not frequent. According to results, the strength of correlation seems to be related to development mode and diet type. The negative egg size-number correlation is stronger when incubation period and fledging time is longer and in birds with longer lifespan. The...

In this study, we tested the long-term and negative effects of microcystin-producing cyanobacterium Microcystis aeruginosa from Vietnam on Daphnia magna under the laboratory conditions. The test organisms were fed with mixtures of green alga Scenedesmus armatus. and toxic M. aeruginosa at different ratios (10% Microcystis + 90% Scenedesmus, 50% Microcystis + 50% Scenedesmus, 100% Microcystis, and 100% Scenedesmus) for over a period of 21 days. The life history traits of the organisms such as, survival, maturation, fecundity were daily recorded. Besides, the intrinsic population rate of D. magna in each treatment was also calculated based on the survivorship, the reproductive age and the clutch size of the animals. The results showed that survival, maturation and reproduction of the D. magna fed with 10, 50 and 100% M. aeruginosa was impaired. Additionally, the intrinsic population rate of the exposed D. magna was lower than that of the control. This study evidenced the adverse effects of toxic M. aeruginosa on both the individual and intrinsic population levels of D. magna. To our knowledge, this is the first report on the chronically detrimental impacts of toxic M. aeruginosa isolated from Vietnam on D. magna and contributed the scientific information on the severe influences of toxic cyanobacteria world wide. / Trong bài viết này, chúng tôi nghiên cứu ảnh hưởng xấu mãn tính của loài vi khuẩn lam Microcystis aeruginosa có khả năng sản sinh độc tố microcysin từ Việt Nam lên Daphnia magna trong điều kiện phòng thí nghiệm. Sinh vật thí nghiệm được cho ăn với hỗn hợp tảo lục Scenedesmus armatus và M. aeruginosa có độc ở các tỷ lệ khác nhau (10% Microcystis + 90% Scenedesmus, 50% Microcystis + 50% Scenedesmus, 100% Microcystis, và 100% Scenedesmus) trong thời gian 21 ngày. Các đặc điểm vòng đời của sinh vật bao gồm sức sống, sự thành thục, sức sinh sản được theo dõi hàng ngày. Bên cạnh đó, tỷ lệ phát triển quần thể của D. magna trong từng lô thí nghiệm cũng được tính toán dựa vào sức sống, tuổi sinh sản và kích cỡ sinh sản của sinh vật. Kết quả cho thấy, sức sống, tuổi thành thục và sự sinh sản của D. magna cho ăn với 10, 50 và 100% M. aeruginosa bị ảnh hưởng xấu. Bên cạnh đó, tỷ lệ phát triển quần thể của D. magna trong lô phơi nhiễm thấp hơn so với đối chứng. Nghiên cứu này chứng minh ảnh hưởng xấu của M. aeruginosa có độc lên cả hai mức độ cá thể và quần thể của D. magna. Theo hiểu biết của chúng tôi, đây là báo cáo đầu tiên về ảnh hưởng xấu mãn tính của M. aeruginosa có độc phân lập từ Việt Nam lên D. magna and đóng góp thêm thông tin khoa học cho những ảnh hưởng nghiêm trọng của vi khuẩn lam có độc trên khắp thế giới.

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Des souris aux baleines en passant par les humains, la diversité écologique des mammifères placentaires est des plus fascinantes. Bien qu'il s'agisse là d'un des groupes les plus étudiés, leur origine fait pourtant l'objet de bien des mystères. Leurs relations de parenté les plus basales restent en effet incertaines, et l'on ignore encore beaucoup du mode de vie qu'avaient nos ancêtres du Crétacé, ces mammifères placentaires qui auraient côtoyé les dinosaures pendant plus de 30 millions d'années.Afin d'aborder ces questions, cette thèse a utilisé l'outil de la génomique comparative. L'une de ses principales originalités est la prise en compte d'un distorteur majeur de notre évolution moléculaire: la conversion génique biaisée. Truquant la loterie génétique, ce mécanisme associé à la recombinaison méiotique avantage les nucléotides G et C au détriment des nucléotides A et T. Façonnés par son influence, nos paysages nucléotidiques présentent ainsi ponctuellement des taux de GC anormalement élevés.Jusque là, ce phénomène n'avait été étudié que chez une poignée d'organismes modèles. Son analyse chez plus d'une trentaine de génomes mammaliens a mis en évidence une série de résultats clés. En particulier, l'évolution du contenu en GC des gènes s'est avéré dépendre de la masse corporelle et la longévité des espèces. E nreliant ainsi évolution moléculaire et traits d'histoire de vie, des reconstructions de séquences ancestrales ont permis d'estimer la durée de vie des premiers mammifères placentaires à plus de 25 ans. Cette longévité va bien au delà de ce que peuvent espérer atteindre les souris ou musaraignes actuelles, des animaux au mode de vie pourtant jusqu'ici supposé comme étant proche de celui de nos ancêtres.Parallèlement à ces résultats, une tendance à produire des phylogénies inexactes a été détectée chez les gènes les plus GC-riches. Moins soumis à la conversion génique biaisée, les gènes AT-riches se sont montrés plus fiables, tout en soutenant que les espèces originaires d'Afrique sont situés à la base de l'arbre des placentaires. Ce résultat suggère ainsi la possible résolution d'un des noeuds les plus controversés de notre histoire évolutive.Du simple nucléotide à la naissance d'une infraclasse de plus de 4000espèces, ce travail révèle comment l'évolution moléculaire peut porter un nouveau regard sur nos origines les plus profondes. / From mice to whales through humans, placental mammals present astunning diversity. Despite being one of the most studied group ever,mysteries persist about their origin. Indeed, their most basalrelationships still remain uncertain, and nothing is really knownabout the lifestyle of our cretaceous ancestors, these placentalmammals which lived side by side with non-avian dinosaurs during 30My.To answer these evolutionnary questions, comparative genomic studiesof placental mammals have been conducted. One of its originalities isto take into account biased gene conversion. Rigging the geneticlottery, this recombination-associated mechanism involves a reparationbias favouring the G and C nucleotides over the A and T ones, whichmark the mammalian genomic landscapes by inducing localized peaks ofGC-content.This phenomenon has been so far studied in few model species. Theexploration of biased gene conversion in more than 30 mammal genomesled to several key results. In particular, GC content evolution hasproved to be correlated to the longevity and the body mass of species.By linking together molecular evolution and life history traits, thereconstruction of ancestral sequences allowed us to estimate alife-span above 25 years for early placental mammals. This value ismarkedly different from that of mice or shrews, although our mammalianancestors have often been represented as such. In addition to these results, GC-rich genes were found to be prone toproduce false phylogenies. Less affected by recombination associatedartifacts, AT-rich genes are shown to be more reliable, and to supportspecies of African origin as the sister group of all other placentalmammals - perhaps resolving one of the most controversial nodes of themammalian tree.From nucleotide to the birth of a 4,000 species infraclass, this workreveals how molecular evolution can shed new light onour deepest origins.

L’étude des interactions hôtes-parasites est devenue un thème de recherche incontournable pour les sciences de l’évolution. Cette coévolution complexe dépend de nombreux compromis évolutifs et peut être grandement influencée par les facteurs environnementaux. Nous nous proposons ici d’étudier les interactions hôtes-parasites à plusieurs échelles, à travers des approches expérimentales et des études en populations naturelles, en étudiant les parasites de la malaria aviaire. Dans un premier temps, nous nous sommes intéressés à l’influence des caractéristiques de l’hôte et notamment au système immunitaire. Le système immunitaire est bénéfique pour l’hôte dans sa lutte contre le parasite, mais peut également engendrer des coûts immunopathologiques. Des traits d’histoire de vie, comme l’âge ou le statut social peuvent modifier la parasitémie au sein des hôtes, sans toutefois avoir d’effet sur la prévalence. Dans un second temps, l’effet de certains facteurs environnementaux a été évalué au sein des interactions hôtes-parasites. La température et la contamination en métaux lourds ont un effet sur la prévalence dans les populations, mais n’affectent pas la parasitémie. Au cours de cette thèse, nous avons également montré l’influence directe des parasites sanguins sur la structure génétique des populations hôtes, notamment au niveau des gènes du CMH. / Host-parasite interactions are one of the main topics in evolutionary sciences. This complex coevolution depends on several trade-offs and can be influenced by environmental factors. Here, we propose to study host-parasite interactions with a multi-level approach, using experimental and natural population studies, focusing on avian malaria parasites. First, we studied the effect of host characteristics, and more precisely the immune system. The immune system confers benefits in terms of protection against the parasite, but can also generated immunopathological costs. Life history traits, like age or social status, appear to modify parasitemia but not prevalence. In a second part, we evaluated the effect of environmental factors on host-parasite interactions. We found that temperature and heavy metal contamination had an effect on population prevalence, but not on host parasitemia. We also showed the direct parasite influence on host population genetic structure, and more precisely on MHC genes.