Prenatal androgens play a key role in sexual differentiation. In humans and rhesus macaques prenatal androgens have been implicated in variation in the development of sexually selected behaviours and cognitive abilities in both males and females. The primacy of prenatal androgens in organising traits linked to sociality suggests great pertinence to the evolutionary substrate that underpins social behaviours in all higher primates. In humans the second-to-fourth digit ratio (2D:4D) is a marker for prenatal androgen effects. Low 2D:4D has been indirectly linked to higher foetal androgens and high 2D:4D has been indirectly linked to lower foetal androgens. Individuals with low 2D:4D express higher competitiveness, promiscuity and more masculinised social cognitive abilities. Low 2D:4D is also more common in polygynous societies. This thesis uses 2D:4D as an anatomical biomarker with phylogenetic comparative methods to investigate eo-variation between prenatal androgen effects and traits linked to sexual selection in haplorrhine primates. In the process, measurements were taken ofthe 2nd and 4th digits of 1286 captive individuals from 74 species. An intra-specific study of2D:4D and dominance ranks in female rhesus macaques is presented and shows that low 2D:4D is more common in higher ranking females. The result suggests that prenatal androgens may be implicated in supporting dominance ranks across generations. A comparison of digit ratios in mother-infant dyads in the same cohort shows heritability of2D:4D to be high; values are similar to humans and more distantly related taxa. Moving to inter-specific analyses: results enclosed provide the first robust evidence that 2D:4D generalise across a taxonomic group and striking parallels are shown between cross-species analyses and results from earlier human 2D:4D studies. In particular, evidence is presented that 2D:4D is lower in polygynous species with higher levels of intra-sexual competition and higher in pair-bonded species with lower levels of intra-sexual competition. These studies also show that 2D:4D eo-varies with both core behavioural characteristics and androgen profiles in catarrhines: in comparison to the great apes, Old World monkeys exhibited low 2D:4D, higher intra-sexual competition and more reactive androgen profiles. These differences might reflect prenatal androgen effects on programming neuro- psychological pathways that potentiate social behaviours and social bonding patterns according to different levels of sexual selection. Focussing on the great apes; 2D:4D is shown to increase from Pongo sp. to Homo sapiens. It is proposed that this reflects a decrease in prenatal androgens and androgen sensitivity across this c1ade. That being the case; fossilised digit bone ratios permitted prenatal androgen effects to be traced across extinct apes and hominins. The findings indicate that Miocene apes might have experienced a down-regulation of the androgen response. Reducing masculinisation is also detected across time in Australopithecus afarensis, but not Ardipithecus ramidus. Evidence from Middle and Late Pleistocene hominins indicates that prenatal androgen effects continued to decrease over evolutionary time. The most recent increase in digit ratios appears to have coincided with shifts in social organisation as modern humans entered a new 'adaptive space' with the advent of agriculture at the beginning of the Holocene. These changes are consistent with hypotheses proposing a 'feminisation' or 'domestication' event coinciding with reductions in dominance and competitive behaviours throughout hominin evolution, right up until relatively recent times. Analyses of 2D:4D identify prenatal androgen effects as strong candidates in the evolution of sexually selected behaviours and social bonding in haplorrhines. Application of2D:4D could thereby improve our current understanding of primate social evolution if incorporated within research into the bio-behavioural processes that underpin sociality across taxonomic groups. Finally, because hominin evolution is so strongly associated with the emergence of specialised cognitive adaptations to cope with changes in social organization, 2D:4D could prove to be a window into our own past.

Dans le contexte de la physiologie comparée de la reproduction, les amphibiens sont peu étudiés. Le travail réalisé durant cette thèse visait à analyser des marqueurs de différenciation testiculaire chez l'urodèle Pleurodeles waltl, dont le déterminisme génétique du sexe (ZZ/ZW) peut être influencé par la température. Nos études ont d'abord porté sur le gène sox9 marqueur de la différenciation testiculaire chez les vertébrés supérieurs. Le gène cloné chez le pleurodèle montre une bonne conservation par rapport aux autres vertébrés. Son expression plus élevée dans la gonade mâle n'apparaît que tardivement suggérant qu'il n'est probablement pas impliqué dans les stades précoces de la différenciation testiculaire. En outre, son expression dans le mésonéphros rend difficile son utilisation comme marqueur de différenciation testiculaire. Nous avons ensuite étudié l'Amh, hormone testiculaire impliquée dans la régression des canaux de Müller chez de nombreux vertébrés. Son expression spécifique de la gonade, précocement plus élevée chez les larves ZZ que les ZW en font un excellent marqueur de la différenciation testiculaire. Le fait que les pleurodèles mâles voient les canaux de Müller persister malgré la présence d'Amh suggère que la fonction primaire de cette hormone était en relation avec la différenciation gonadique et que la fonction de régression des canaux de Müller n'est apparue que secondairement au cours de l'évolution. Ces marqueurs ont été mis à profit pour caractériser le phénotype gonadique lors d'inversions sexuelles ou lors de développements en absence de cellules germinales. Ils ont permis de montrer que les cellules germinales ne semblent pas jouer de rôle dans la différenciation gonadique du pleurodèle / In the context of comparative physiology of reproduction, amphibians are poorly studied. This work was dedicated to the analysis of testis differentiation markers in the newt Pleurodeles waltl, which shows a ZZ/ZW genetic mode of sex determination that can be affected by temperature. First, we studied sox9, a testis differentiation marker well characterized in many higher vertebrates. The gene cloned in Pleurodeles shows a good level of identity with other vertebrates. The testis-enriched expression appears late during the testis differentiation process indicating that it is probably not involved in the early steps of testis differentiation. Its use as a marker of testicular differentiation proved difficult since it is expressed not only in the gonads but also in the mesonephros. Then, we studied amh, a testis hormone responsible for müllerian duct regression in many vertebrates. Its early expression in the gonad, significantly higher in male than in female larvae makes it an excellent marker for testis differentiation. Since in Pleurodeles waltl, Müllerian ducts persist in males, it suggests that during the course of evolution, the function of Amh on the regression of Müllerian ducts appeared secondarily after its role in gonadal differentiation. These markers have been used to characterize the gonadal phenotype during sex reversal, or in gonads developed in the absence of germ cells. They showed that these cells do not seem to play a role in gonadal differentiation of Pleurodeles waltl

La différenciation sexuelle des Isopodes dépend d'une hormone sexuelle protéique, l'hormone androgène (HA), caractéristique des Malacostracés. Cet Insulin-Like Peptide suffit à induire par sa présence la différenciation mâle de ces Crustacés. Nous avons identifié in silico le transporteur circulant de l'HA, l'IGFBP-rP1, chez de nombreuses espèces d'Isopodes ainsi qu'à l'échelle des Crustacés. De la même façon, nous avons identifié deux récepteurs transmembranaires, l'IR1 et l'IR2, issus d'une duplication de gène spécifique des Malacostracés. Les patrons d'expression de ces gènes ont été étudiés sur notre espèce modèle, Armadillidium vulgare. Av-IGFBP-rP1 et Av-IR1 sont exprimés de manière ubiquiste et tout au long du développement. Av-IR2 est aussi exprimé à chaque stade de la différenciation mais ce transcrit est quasi-spécifique des glandes androgènes et ovaires. Une approche par ARNi a confirmé l'implication de ces trois protéines dans la voie de signalisation de l'HA. En effet, l'inhibition de l'HA, Av-IGFBP-rP1 et Av-IR1 provoquent l'hypertrophie des glandes androgènes, suggérant leur implication dans une boucle de rétro-contrôle de l'HA. L'inhibition de Av-IR2 semble seulement provoquer la différenciation d'ouvertures génitales femelles. Ces phénotypes sont comparables à ceux des intersexués mâles induits par la bactérie féminisante endogène Wolbachia. Nous montrons cependant que la bactérie altère seulement l'expression de l'HA et pas celle des récepteurs. Enfin, nous avons testé l'effet du bisphénol A mais nous n'observons pas d'altération de la différenciation sexuelle des larves lors d'expositions à ce perturbateur endocrinien exogène. / Sexual differentiation in Isopods relies on a proteinaceous sex hormone called androgenic hormone (AH), specific to Malacostracans. This Insulin-Like Peptide induces male differentiation by its mere presence in these Crustaceans. We identified in silico the circulating carrier of the AH, called IGFBP-rP1, in many Isopod species, but also on the crustacean scale. Similarly, we identified two transmembrane receptors, IR1 and IR2, coming from a gene duplication specific to Malacostracans. The expression patterns of these genes were investigated in our model species, Armadillidium vulgare. Av-IGFBP-rP1 and Av-IR1 are broadly expressed in the animal and throughout development. Av-IR2 is also expressed at each developmental stage but this transcript is almost specific to androgenic glands and ovaries. An RNAi approach has confirmed the implication of these three proteins in the AH signalling pathway. Indeed, the inhibition of AH, Av-IGFBP-rP1 and Av-IR1 induces androgenic gland hypertrophy, suggesting their implication in an AH feedback loop. Av-IR2 inhibition seems to provoke the differentiation of female genital apertures only. These phenotypes are similar to those of male intersexes induced by the endogenous feminizing bacterium Wolbachia. Yet, we show that the bacterium alters the expression of the AH only and not the one of its receptors. Finally, we have tested the effect of bisphenol A but we observe no alteration of the sexual differentiation in larvae upon exposition to this exogenous endocrine disruptor.