Selection operates when the variability among individuals in heritable traits translates to differences in the number of offspring that survive to breed, which is a close estimate of fitness. Consequently, the outcome of sexual-selection should be higher reproductive success for individuals with a greater expression of the selected traits. In this thesis, the relationship between some male spotless starling (Sturnus unicolor) traits and reproductive success was assessed. A particular focus was given to the role of throat feathers (TF) as sexually selected trait. The study was conducted in a wild population using a correlative approach in 2004, while in 2005 and 2006 the TF of males were experimentally shortened. The genetic parentage of the offspring was required for determining the reproductive success of males. Nine highly polymorphic microsatellites (with 11.7± 3.2 alleles per locus) were developed and optimised for this species. Parentage analyses were conducted in NEWPAT XL and CERVUS 3.0.3 and confirmed using observational data. Eighty-five percent of the offspring had at least one parent assigned. The levels of intra-specific brood parasitism, extra-pair paternity and quasi-parasitism were 7%, 7% and 1% of the offspring, respectively. Polygamy levels decreased with year, as the study population matured. The correlative study showed that males with longer TF and with better condition had a higher probability of reproducing and sired more offspring, but their offspring were not of higher quality as measured by their weight and immune response to phytohaemagglutinin. Polygynous males were also in better condition. In the experimental study, males in better condition had a higher chance of reproducing and sired more fledglings. Conversely, males with reduced TF sired significantly fewer eggs and lighter fledglings than control males. Body condition and TF length are shown to be good predictors of reproductive success and TF length is shown to be under sexual selection.

Mate choice plays an important role in sexual selection and speciation. The evolution of mate choice is intriguing in cases where choosy individuals gain little except for genetic material from the mate and where the trait used as a criterion for the choice is costly to its bearer. The sensory exploitation hypothesis is an interesting idea that applies to such cases because it suggests that sexual preferences may arise as side-effects of preferences that are under selection in other contexts. The role of mate choice in speciation is strong but is debated because the reasons for population divergence in mate preferences and sexual traits are sometimes hard to explain. Also in this context sensory exploitation offers a potential explanation in that a link between natural and sexual selection may result in divergence in sexual selection whenever populations differ in natural selection. In this thesis, I test several aspects of this hypothesis in a species of fish, the swordtail characin (Corynopoma riisei). In this species males display a flag-like ornament that grows from the operculum. Because females respond to this ornament by biting at it, it has been proposed to act as a food-mimic. By manipulating female food type and quantity, and testing the resulting female preference for the male ornament, I find support for the theory that the preference has evolved through sensory exploitation and that females indeed appear to relate the ornament to a food item. Furthermore, I show that sensory exploitation can lead to morphological divergence among natural populations in this species. Apart from the flag-ornament, other courtship signals are also investigated. The results show that the relative importance of different signals may vary depending on receiver motivation. This suggests that various aspects of both male courtship signals and the conditions during which they are being signalled should be considered to gain a full understanding of mate choice and its role in sexual selection and speciation.

Chapter 1: Relative Concerns and the Choice of Fertility Empirical research has shown that people exhibit relative concerns, they value social status. If they value their children's status as well, what effect will that have on their decisions as parents? This paper argues that parents and potential parents are in competition for status and rank in the generation of their children; as a consequence richer agents may cut back on the number of children they have and invest more in each child to prevent children of lower income agents from mimicking their own children. This effect need not be uniform so that equilibrium fertility may e.g. be a U-shaped function of income, even when agents would privately like to increase fertility when they receive greater income. These findings have wide ramifications: they may contribute to our understanding of the working of the demographic transition; they also suggest that the low fertility traps seen in some developed countries are rather strongly entrenched phenomena; and they o er a new explanation for voluntary childlessness. Chapter 2: Relative Concerns and Primogeniture While pervasive in the past, differential treatment of children, i.e. different levels of attention and parental investments into children of the same parent, has become rare in modern societies. This paper offers an explanation based on technological change which has rendered the success of a child more uncertain for a parent who is deciding on how much to invest into each of his children. Within a framework of concerns for social status (or relative concerns), agents decide on how many children to have and how much to invest in each child. When their altruism towards each child is decreasing in the total number of children, it is shown that they may solve the trade-off between low investment, high marginal return children (that come in large numbers and hence hurt parental altruism) and high investment, low marginal return children (that come in low numbers) by demanding both types and hence practice differential treatment. Uncertainty over status or rank outcomes of children reduces the range of equilibrium investment levels intro children so that the difference in the numbers they come in is reduced. Eventually the concern for return dominates and differential treatment disappears. Chapter 3: Co-Evolution of Institutions and Preferences: the case of the (human) mating market This paper explores the institutions that may emerge in response to mating preferences being constrained in their complexity in that they can only be conditioned on gender not other characteristics of the carrier of the preferences. When the cognitive capacity of the species allows a sophisticated institutional setup of one gender proposing and the other accepting or rejecting to be adopted, this setup is shown to be able to structure the mating allocation process such that preferences evolve to forms that, conditional on the setup, are optimal despite the constraint on complexity. Nature can be thought of as delegating information processing to the institutional setup. In an application to humans it is shown that the mechanism of the model can help explain why men and women may exhibit opposed preferences in traits such as looks and cleverness. The anecdotal fact that women do not marry down while men do can be interpreted as a maladaptation of female preferences to modern marriage markets.

This thesis presents two studies where natural and sexual selection have interacted to evolve sexual behaviours. The thesis uses mathematical modelling to understand how these forces have caused each behaviour to evolve. This is useful because the results allow for reflection on the potential role of sexual selection in adaptation of these species to a changing environment. The first study is of early male arrival to spring breeding grounds in migratory avian species, this is termed protandry. The study explores the main hypotheses for avian protandry and then tests the susceptibility of each hypothesis to changing environment. The second study is of convenience polyandry in species where there is conflict over mating rate. Females have multiple strategies to avoid harassive males but strategies vary in cost and success rate; she must balance her strategy use to minimise her fitness depreciation. The study identifies the main factors that cause convenience polyandry to evolve and paves the way for future studies to investigate if sexual selection over resistance strategy provides these species a future advantage in adaptation to a changing environment.

In this thesis I set out to further our understanding of two broad questions, 1) why it is that sexual selection favours the evolution of particular traits and 2) why do the patterns of sexual selection on such traits differ between groups and populations? Specifically, I focused on the role that variation in intrasexual competitive structure, the non-random distribution of socio-competitive environments across individuals, plays in shaping variation in the operation of sexual selection both within and across populations. I explore the roles of three main determinants of competitive structure, namely; population structure, polyandry and non-random variation in the distribution of the intensity of competition. To achieve this, I used a combination of empirical and theoretical tools, using the model system Red junglefowl, Gallus gallus. Throughout this thesis I both develop and employ network quantitative tools as a framework to describe variation in intrasexual competitive structure. Overall, this thesis demonstrates a complex relationship between competitive structure and the operation of sexual selection. This structure can modify the strength and direction of sexual selection operating on phenotypic traits, obscure the operation of selection at the population level and influence the relative roles of pre- and post-copulatory sexual selection. Furthermore, this thesis explores how differences in local ecology can shape competitive structure itself and in turn shape sexual selection. In doing so, this thesis sheds some light on the role that variation in competitive structure may play in shaping the operation of sexual selection both within and between populations and generating the great diversity in sexually-selected traits and behaviours between populations.

The natural world consists of a vast array of forms, some more plentiful than others, yet our understanding of the processes responsible the production of biological diversity remains surprisingly limited. Here I combine novel datasets with powerful phylogenetic modeling techniques and computer simulations to test the effects of both biotic and abiotic factors on the dynamics of species radiations and the evolution of organism traits in birds. In the first part of this thesis, I develop our understanding of the importance of abiotic factors for diversification by showing that in the early stages of lineage diversification at least, rapid adaptation to novel climatic conditions is likely to represent a prominent driver of avian diversification. In the second part I concentrate on the role of biotic factors, in particular that of sexual selection. I show that not only is sexual selection associated with accelerated rates of speciation and secondary sympatry—as well as faster rates of net diversification across the entire avian tree of life—but also that across-species variation in rates of phenotypic evolution is best understood with reference to the focus and intensity of sexual selection. Finally, given that the relative importance of such processes appears to vary predictably across latitudes, in the final part of the thesis I argue that latitudinal differences in the speciation process offers a potentially powerful explanation for conflicting viewpoints regarding the contribution of speciation to high tropical diversity. Overall, this work provides fresh insight into the processes governing broad-scale patterns in biodiversity.

Generally it is assumed, that sexual selection drives the evolution of elaborate traits. The strength of sexual selection has traditionally been attributed to varinace in reproductive success among individuals. This variance is mainly caused by the number of mating partners and the number of sired offspring. Both males and females can increase their reproductive success by alternative reproductive strategies - extrapair copulations and intraspecific brood parasitism. In our study we tested the relationship between male ornamentation and success in extra-pair and within-pair paternity and the total male reproductive success in barn swallow (Hirundo rustica), a socially monogamous species with high levels of extrapair paternity. The results suggest more colourful throat to indicate male reproductive success. Dark rusty males were less often cuckolded and they have higher total fertilization success than drab ones. Tail length did not affect neither within- nor extra-pair fertilization success, however, previous studies have concluded that reproductive success of male barn swallows is positively related to the tail ornaments. Our results confirm that extra-pair paternity considerably increase variance in reproductive success among barn swallow males. We show that within-pair success may increase the...

Elaborate morphological ornaments can evolve if they increase the reproductive success of the bearer during competition for mates. However, ornament evolution is incredibly rare in females, and the type and intensity of selection required to develop female-specific ornamentation is poorly understood. The main goals of my thesis are to clarify the relationship between the type and intensity of sexual selection that drives the evolution of female ornamentation, and investigate alternative hypotheses that might be limiting or contributing to the development of female ornaments. I investigated the ecology and evolution of female-specific ornaments within and between species of dance flies from the subfamily Empidinae (Diptera: Empididae). The dance flies display incredible mating system diversity including those with elaborate female-specific ornaments, lek-like mating swarms, aerial copulation and nuptial gift giving. To elucidate the form of sexual selection involved in female-ornament evolution, I experimentally investigated the role of sexual conflict in the evolution of multiple female- specific ornaments in the species Rhamphomyia longicauda. Through manipulative field experiments, I found that variation in the attractiveness of two ornaments displayed by females indicates that sexual conflict, causing a coevolutionary arms race, is an important force in the evolution of multiple extravagant female ornaments. Using R. longicauda again, I tested for a role of functional load-lifting constraints on the aerial mating ability of males who paired with females displaying multiple large ornaments. I found no evidence of functional constraints influencing the mating opportunities of elaborately ornate females, but instead discovered a relationship consistent with positive assortative mating for mass. Biased sex ratios are predicted to increase the intensity of sexual selection in a population, which in turn, is predicted to influence the evolution of ornamentation. I measured the incidence and prevalence of vertically transmitted symbiotic bacteria that has been observed to distort the sex ratio in other Dipteran hosts. While my survey revealed that symbionts occur at high incidence and variable prevalence across dance fly hosts, I found no effect of symbiont infection levels on population sex ratios, or female- specific ornament evolution. Further investigation into the relationship between sex ratios and female-ornament evolution using the comparative method revealed that the operational sex ratio (OSR) of a population did not predict continuous measures of female ornamentation across species. However, female-ornament evolution did predict male relative testis investment across species indicating that female ornaments likely indicate increased levels of polyandry. My thesis reveals that sexual selection theory developed to describe male-specific ornament evolution cannot readily be translated to apply to females. I show that male mate choice, rather than functional constraints or ecological associations with bacteria, is likely driving the evolution of female-specific ornaments. I also identify sexual conflict as an important selective force in the evolution of female-specific ornaments.

<p>QCR 20161026</p>

Les interactions comportementales entre hétérospécifiques, lors du contact entre deux populations auparavant isolées, sont source de nouvelles pressions de sélection sur les traits affectant ces interactions. Les traits impliqués notamment dans les interactions reproductives et compétitives évoluent en fonction de ces pressions et ces adaptations peuvent influencer le processus de spéciation. La communication entre individus joue un rôle particulièrement important dans la régulation des interactions comportementales intra et inter-spécifiques. L'évolution de la reconnaissance spécifique peut notamment permettre d'adapter les réponses comportementales lors des rencontres en fonction de l'identité spécifique des individus. Les études empiriques présentées ici ont eu pour objectif de tester, chez un organisme modèle (deux sous espèces de la souris domestique), le rôle de la sélection sexuelle contre les hybrides et de la compétition mâle-mâle par interférence dans la mise en place de l'isolement reproducteur. Nos résultats montrent que la sélection sexuelle peut avoir un double effet dans la zone hybride entre Mus musculus musculus et M. m. domesticus : réduire la fitness des hybrides, et limiter le flux de gènes à travers la zone. La compétition par interférence ne semble par contre pas avoir un rôle important dans l'évolution de la reconnaissance spécifique relativement aux pressions émergeant des interactions reproductives. Nos résultats mettent également en évidence des asymétries dans l'intensité des préférences homogames en zone de contact, qui pourraient être représentatives de pressions de sélection inégales entre sexes et entre sous-espèces. Cette dissertation se clôt sur une discussion sur les interactions entre différents processus évolutifs suite à un contact, et sur la notion de reconnaissance spécifique. / Behavioural interactions between heterospecifics, when two previously isolated populations come into contact, generate new selective pressure on traits involved in those interactions. Particularly, the traits involved in reproductive and competitive interactions evolve due to this selection, and these adaptations can affect the speciation process. Communication plays an important role in the regulation of behavioral interactions, both between and within species. Evolution of species recognition allows behavioral adjustment to the species of the encountered individuals. The empirical studies presented here aimed to test, on a model organism (two house mice subspecies), the role of sexual selection against hybrids, and of male-male interference competition, in the evolution of reproductive isolation. Our results show that sexual selection can act in th hybrid zone between Mus musculus musculus and M. m. domesticus, by reducing hybrid fitness, and by impeding gene flow through the zone. Interference competition however do not seem to be an important driver of the divergence of species-specific signals in the contact zone, and reinforcing selection is probably at the origin of this character displacement. Our results also enlighten asymmetries in homogamous preferences intensity, which could be due to differences in selective pressures depending on sex an subspecies. This dissertation ends on a discussion on interactions between process at play at secondary contact, and on the notion of species recognition.