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Evaluation de l’importance de la sélection sexuelle sur les traits femelles et de ses conséquences sur la viabilité des populations – SEX-FEM-POP

Submission summary

Sexual selection, as traditionally viewed, is predicted to increase, rather than decrease, population adaptive potential. This prediction stems from the fact that the good-genes process allows the selection against deleterious mutations to affect males more than females. This process would entail a low demographic price: given the asymmetry between male and female gamete size, population growth is thought to rely mostly on the high energetic investment of females, male contribution being restricted to gene transmission. This asymmetry leads to the evolution of male exaggerated secondary traits and female mate choice. Although these classic sex roles are indeed frequent in nature, they are by no means universal. In a vast number of species, sexual dimorphism is weak or absent and females show conspicuous traits. Moreover, a growing number of studies suggest a male mate choice in species without any evidence of sex role reversal. It is therefore now time to challenge the asymmetrical view of sexual selection and explore theoretically and empirically whether sexual selection is an anecdotic or widespread force shaping female traits and whether it has any consequences on population dynamics. 1) Species where females show conspicuous traits are good models to explore this question. To date, there is no consensus on how such female traits are maintained and we still ignore the environmental and life history traits associated to the occurrence of these traits. A common explanation rooted in the asymmetry paradigm is that female traits emerge as by-products of sexual selection in males. However, conspicuous female traits would only persist if the genetic correlation between sexes were one, which is an unlikely situation. Alternative to the by-product hypothesis is that female traits themselves serve as signals for male attraction (ornaments) or during female-female competition (badges of status). Our first objective will be to investigate whether inter and intra sexual selection operates in females and under which social and environmental conditions. 2) Surprisingly few experimental and long-term longitudinal studies have investigated the information contained in female ornaments. Consequently, we still know relatively little about the occurrence of direct or indirect benefits obtained through male mate choice. Such information is essential to discern whether male mate choice is adaptive or merely a by-product of a genetic correlation with female mate choice. Our second objective will thus be to investigate the signalling value of conspicuous female traits and to question the mechanisms insuring their honesty. 3) Theoretical studies of the population-level consequences of sexual selection are highly dependent on an extreme version of the asymmetry assumption since they assume that the costs of sexually selected traits are paid exclusively by males, which do not contribute to population growth. Our third objective is to investigate, both theoretically and empirically, how biparental investment, and sexual selection on female traits may impact the community dynamic and adaptive potential of natural populations. This is a completely new area in which neither theoretical nor empirical data have been collected so far. We will use the most powerful and robust approaches known in evolutionary ecology to obtain key answers to each of our three main objectives. We will perform (i) analyses of robust long term longitudinal data-bases (about 30 years) with capture-mark-recapture statistics and quantitative genetics, (ii) experiments, (iii) comparative methods and (iv) modelling. Each of the researchers in our team is an expert in at least one of the complex techniques proposed. Their expertise is complementary: field work, long-term population monitoring and experimentation (C. Doutrelant, A. Gregoire, P. Perret, M. Lambrechts and B. Doligez); capture-recapture statistical methods for individuals and communities (respectively A. Grégoire and T. Boulinier); comparative analyses (Doris Gomez and Rita Covas); theoretical modelling and population genetics (P. David); quantitative genetics analyses (A. Charmantier); and visual modelling (Doris Gomez). With the exception of the theoretical models, we will focus our project on birds. Since a vast majority of (bird) species present a limited sexual dimorphism, we will study conspicuous traits that are present in both males and females: plumage, beak, and leg coloration. We will also study a trait specific to females: eggshell coloration. This latter trait is particularly interesting to study in the light of the current raging debate about the selective forces (natural, sexual) involved in its evolution.

Project coordinator

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

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Beginning and duration of the scientific project: - 0 Months

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