<p>A long-held assumption in animal behavior is that females and males differ fundamentally in their mating strategies. Females are thought to be more choosy because female reproduction typically is limited by parental investment. Males, on the other hand, are expected to compete among themselves for access to females or resources, since male reproduction is limited primarily by mating access. This dichotomy is challenged by the increasing realization that males can be choosy and females also compete aggressively. It remains unclear, however, if and how selection acts on aggressive behavior in the context of intrasexual competition among females (reviewed in Chapter 1). In this thesis, I use a population of free-living tree swallows (<i>Tachycineta bicolor<i>) to test predictions about the selective pressures shaping aggressive behavior in females. First, using an experimental manipulation of nest site availability, I demonstrate that more aggressive females have a competitive edge in acquiring nestboxes, a critical limiting resource required for breeding (Chapter 2). This result shows that more aggressive females are more likely to breed and, thus, that females experience direct selection to be aggressive in the context of competition for mating opportunities. Next, I demonstrate a fitness cost of female aggression (Chapter 3): high levels of aggression in females are not associated with the quantity of offspring, but instead, more aggressive females had offspring of lower quality (i.e. reduced mass). Using a cross-fostering approach, I explore the causal link between female aggression and offspring mass, and I find that a trade-off between female aggression and maternal care best accounts for this cost of aggression. Site differences may create variation in how selection shapes female aggression, but the overall finding that more aggressive females have lower quality offspring indicates that this cost may work counter to selection favoring aggressive behavior in the context of competition over nestboxes. Understanding the evolution of female aggressiveness in a biparental system is incomplete without examining how males may alter the selective environment shaping female behavior. In Chapter 4, I explore the potential role of a female's mate in offsetting the costs of aggression. Males appear to mitigate these costs for their female partners, but not by compensating for poor parenting by aggressive females. Instead, females invest more heavily in reproduction, laying more and larger eggs, when mated to a male that is more different from her own phenotype. If this differential investment outweighs the cost of aggressiveness in terms of offspring quality, then male phenotype may play a key role in understanding the selective pressures shaping the evolution of aggressive behavior in females. Altogether, this dissertation explores the costs and benefits of female aggressive behavior. The focus on aggressiveness as a sexually selected trait in females provides a much needed parallel to the wealth of information already known about the selective pressures shaping sexually selected traits in males.</p> / Dissertation

Many critics have examined the shifting nature of female friendship in Jane Austen’s Emma from cultural and historical angles. However, a comprehensive scientific analysis of female-female alliance and competition in the novel remains incomplete. The Literary Darwinist approach considers the motivations of fictional characters from an evolutionary perspective, focusing primarily on human cognition and behaviors linked to reproductive success, social control, and survival. While overt physical displays of male competition are conspicuous in the actions of the human species and those of their closest primate relatives, female aggression is often brandished psychologically and indirectly, which makes for a much more precarious study. In this paper, cultural criticism and evolutionary psychology work together to unravel the most complicated and arcane layers of intrasexual competition between women in Emma. Ultimately, this dual interpretation of the novel steers readers towards a deeper understanding of Emma Woodhouse’s imperiled friendships, and by extension, their own.

Chez les espèces où mâles et femelles portent des traits voyants et élaborés, les traits observés chez les femelles peuvent être des sous-produits non-fonctionnels de la sélection sexuelle exercée sur les traits mâles ou alors être directement soumis à la sélection. Cette thèse a eu pour objectif de tester l'hypothèse de sélection sexuelle chez les femelles de Mésange bleue (Cyanistes caeruleus) sur trois traits présents chez le mâle et la femelle : (1) la coloration structurelle UV/bleue de la tête, (2) la coloration jaune basée sur les caroténoïdes de la poitrine et (3) l'agressivité. Pour cela, nous avons testé expérimentalement (1) le lien entre les traits colorés et le transfert de composants potentiellement bénéfiques dans les ufs, (2) la condition-dépendance des traits colorés, (3) l'utilisation de la coloration du plumage dans les interactions femelle-femelle et (4) le lien entre l'agressivité des femelles et leur investissement dans la reproduction. Enfin, nous avons exploré le rôle potentiel des couleurs femelles dans le choix de partenaires mâle en testant le lien entre la couleur UV/bleue des femelles et le nombre de jeunes issus de copulations hors couple et l'appariement selon la couleur bleue et jaune dans notre population. Nos résultats suggèrent (1) qu'il existe un lien entre la qualité maternelle et la coloration de leur plumage, (2) que les couleurs UV/bleues et jaune du plumage sont conditions-dépendants, (3) que les UV/bleus de la tête sont utilisés comme badge de statut dans les interactions femelle-femelle, (4) qu'il pourrait exister un compromis entre l'agressivité femelle et son investissement dans la reproduction et (5) qu'il existe un potentiel choix mutuel de partenaires basés sur les couleurs. Au final, cette thèse a ainsi permis de mettre en évidence que chez une espèce où mâles et femelles sont ornementés, les traits colorés femelles ont le potentiel d'évoluer sous l'effet direct de la sélection sexuelle. / In mutually ornamented species, female conspicuous traits could be non-functional by-products of sexual selection acting on male traits or could be directly under selection. The aim of this PhD was to test the hypothesis of sexual selection in Blue tit (Cyanistes caeruleus) females on three traits present in both males and females: (1) the structural coloration of the UV/blue crown, (2) the yellow chest coloration based on carotenoids and (3) aggressiveness. To do so, we experimentally tested (1) the links between plumage coloration and the transfer of potentially beneficial components in egg yolks, (2) the condition-dependence of the plumage coloration, (3) the use of the plumage coloration in female-female interactions and (4) the link between female aggressiveness and investment in reproduction. Finally, we explored the role of female plumage coloration in male mate choice by testing the link between female UV/blue crown coloration and the n umber of extra-pair young in the nest and by estimating whether the individuals were assortatively mated in respect of their yellow and blue coloration in the studied population. Our results suggest that (1) there is a link between female plumage coloration and maternal quality, (2) plumage UV/blue and yellow coloration is condition-dependant, (3) the UV/blue crown is used as a badge of status in female-female interactions, (4) there could be a trade-off between female aggressiveness and female investment in reproduction and (5) there is a potential mutual mate choice based on both coloration. So, this PhD supports the hypothesis that in a mutually ornamented species, female ornaments are potentially under direct sexual selection.

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Chez les espèces sociales, les individus des deux sexes peuvent interférer avec la sexualité et les alliances sociales des femelles, ce qui peut influencer les stratégies reproductives des femelles. Un regain d'intérêt récent pour l'action de la sélection sexuelle chez les femelles a mis en évidence que la compétition entre femelles pour monopoliser les ressources reproductives, comme les partenaires sexuels ou les soins aux petits, est prévalente. Cependant, jusqu'à présent, la compétition reproductive entre femelles a reçu peu d'attention chez les espèces polygynes. Nous avons donc étudié les déterminants de la compétition reproductive entre femelles dans une société primate polygyne, dans une population naturelle de babouins chacma, en Namibie. Nos résultats montrent que l'agression est plus intense entre les femelles qui sont en synchronie reproductive et associées à un même mâle, avec qui elles entretiennent des liens sociaux et sexuels préférentiels, et qui est souvent le protecteur et le père de leur petit. De plus, les femelles gestantes et en lactation harcèlent les femelles qui copulent avec leur mâle, probablement afin d'empêcher de nouvelles conceptions avec celui-ci. La compétition pour les soins des mâles semble donc contribuer à façonner les stratégies reproductives des femelles chez les espèces polygynes où ceux-ci apportent d'importants bénéfices aux femelles. Nous avons ensuite étudié les contraintes exercées par les mâles sur la sexualité des femelles. Mâles et femelles ont souvent des optimaux reproductifs divergents, donnant lieu à l'expression d’un conflit sexuel. Chez certaines espèces, les mâles recourent à la coercition sexuelle en agressant les femelles régulièrement afin de les obliger à s'accoupler avec eux-mêmes, ou de les empêcher de s'accoupler avec leur rivaux. Nous avons testé si l'agression dirigée par les mâles vers les femelles a une fonction de coercition sexuelle chez le babouin chacma. Nos résultats indiquent que l'agression des mâles vise en particulier les femelles sexuellement réceptives, augmente le succès d'accouplement immédiat des mâles avec la femelle harcelée et ses chances de la monopoliser lors de l'ovulation, à l'appui de l'hypothèse de coercition. Dans l'ensemble, cette étude permet d'améliorer notre compréhension des déterminants, de l'intensité, et des conséquences évolutives des contraintes sociales qui s'exercent sur la sexualité des femelles dans une société primate polygyne. Elle montre également que les conflits reproductifs jouent un rôle primordial pour structurer les relations entre les femelles d’une part, et entre les sexes d’autre part. / In group-living species, individuals of both sexes can interfere with the sexuality and social alliances of females, which may profoundly influence their reproductive strategies. Renewed attention in the operation of sexual selection on females shows that competition among females to secure reproductive resources, such as mates or allomaternal care, is common. However, to date, female reproductive competition has received little attention in polygynous species. In an attempt to fill this gap, we investigated the determinants of female reproductive competition in a polygynous primate society, the chacma baboon, focussing on a wild Namibian population. Our findings highlight that the frequency of aggression is most intense among females who are reproductively synchronous and who share the same male carer of their offspring. Females also harass sexually receptive females who attempt to mate with their offspring’s carer, likely to prevent further conceptions with him. Overall, competition to secure male carers seems to play an important role in shaping female reproductive strategies in polygynous species where males may provide females with important fitness benefits. We then examined constraints exerted by males on female sexuality. Males and females often have diverging reproductive optima, which underpins sexual conflict. In some species, males may use sexual coercion, in the form of repeated aggression before or during female sexual receptivity to induce females into mating or prevent them from mating with rivals. Here, we tested whether male aggression directed at females represents sexual coercion in chacma baboons. In support of the sexual coercion hypothesis, we found that male aggression against females is most intense when females are sexually receptive, increases male mating success with the harassed female on the short-term, and increases his chances to monopolize her around ovulation on the longer-term. Altogether, these results shed light on the determinants, intensity and evolutionary consequences of social constraints exerted on female sexuality in polygynous primates, and highlight that reproductive conflicts play a primary role in structuring female-female and male-female relationships.