Sexual selection acts on traits that increase the reproductive success of an individual in competition with other individuals of the same sex over reproductive opportunities, through intra-sexual competition and inter-sexual mate choice. Because males benefit more from remating than females, they are subject to more intense sexual selection. Modern genetic tools have shown that females often mate promiscuously, thus prolonging sexual selection after insemination through intra-sexual (sperm competition) and inter-sexual (cryptic female choice) episodes. Despite increasing interest in post-copulatory sexual selection, the implications of sperm competition, cryptic female choice and underpinning mechanisms remain little understood. This thesis adopts an integrated approach to quantify the relative importance of post-copulatory episodes in the operation of sexual selection, elucidate their proximate mechanisms in the red junglefowl Gallus gallus. By combining behavioural observations of replicate groups with paternity data, I show that female promiscuity decreased the total opportunity for sexual selection in a group, but accounts for an unexpectedly large proportion of the variance in male reproductive success. By comparing the operation of sexual selection on multiple male traits, I show that post-copulatory sexual selection reinforced pre-copulatory sexual selection for male social dominance and that female preferred to mate with compatible males. I used experiments to study the mechanisms of post-copulatory sexual selection by studying the effect of seminal fluid in sperm competition and cryptic female choice in relation to male status and relatedness. Following previous work indicating that seminal fluid products influence sperm quality in this species, I tested in vivo whether the seminal fluid of an ejaculate acts differentially towards sperm from the same ejaculate and rival sperm, and found no evidence for this idea. Finally, I show that cryptic female choice can drastically bias the outcome of sperm competition, and that female fowl might bias paternity toward unrelated males.

The evolutionary processes of sexual selection are investigated in this study by developing a new model for the evolution of epigamic traits and examining the effects of male-male competition, female choice and filial cannibalism in a field population of the Cortez damselfish (Stegastes rectifraenum). Two general processes have been proposed to explain the evolution of epigamic traits: the good genes process and the Fisherian process. A third process leading to the evolution of epigamic traits is presented here: the good parent process. Epigamic traits arise through this process by clarifying the differences in non-heritable parental quality among potential mates. A population genetic model is developed, which further suggests that increases in the frequency of good fathers in the population and phenotypic plasticity enhance the evolution of a good parent trait. The relative strengths of female choice and male-male competition were studied in S. rectifraenum by direct observation of reproductive behavior, and through field experiments. Male body size was found to be the single most important correlate of male reproductive success. Males were removed from their territories to determine the extent to which the vacant territories were valued by other local males. All of the territories were quickly recolonized by new males and sites that initially showed the highest reproductive success continued to be the most successful when new residents were present. A second experiment involved standardizing nests in 30 territories. Under these conditions male body size was no longer correlated with reproductive success, indicating that females are strongly influenced by variance in natural nest sites. Consequently, male-male competition over territories containing high quality nest sites, in combination with female choice of those sites, generates the observed correlation between male body size and reproductive success. Partial clutch filial cannibalism by male S. rectifraenum was studied in the same population. A group of custodial males were fed eggs, while controls remained unfed. Both groups were dissected on the next day to determine the number of eggs in their stomachs. Fed males had significantly fewer eggs in their guts, indicating that they indeed feed on the eggs they guard, rather than take them incidently during nest maintenance activities. A second egg feeding experiment showed that male behaviour and reproductive success are little affected by filial cannibalism; thus it is hypothesized that the energy gained by this behaviour is channelled primarily into growth and survival.

Over the last century, sexual selection has grown from a controversial theory into a vast field of theoretical and empirical research. Although Darwin outlined two major mechanisms within his theory, male-male competition and female mate choice, the latter has promoted a wealth of research by virtue of its complexity. Despite decades of research into how female preferences and sexually selected traits have evolved, there is still little consensus as to why females prefer the males they do. Preferences are thought to evolve from either direct selection on the preference, as females themselves benefit directly from mating with a preferred male, or through indirect selection on the preference via offspring fitness. In all cases however, female preferences should compensate for the costs of discriminating between potential mates, if they are to remain overall beneficial. The fitness benefits of mating with preferred males were investigated here using the fruitfly Drosophila simulans, employing a range of behavioural, phenotypic and quantitative genetic approaches. The findings presented here indicate that female Drosophila simulans do not gain directly from mating with a preferred male. Multiple mating can increase fecundity, although costs from male harassment can reduce the net benefit. They also indicate that females may benefit indirectly from mating with attractive males as attractiveness is heritable and sons of preferred males are themselves preferred. There is also evidence that attractive males are successful in both the pre- and post-copulatory sense, as preferred males are better sperm competitors than less-preferred males. However, although there appear to be benefits from preferred males via their sons, there appear to be no benefits from males via their daughters’ fitness. These findings collectively indicate that female preferences in Drosophila simulans are driven by indirectly selected benefits (via Fisherian sons), and that females benefit directly from mating multiply.

Ageing is the progressive decline in physiological performance with age, which is almost universal amongst multicellular organisms. While understanding ageing is an important aim in biological research, our current understanding of how and why we age is incomplete. In this thesis, I examine how sexual selection affects the evolution and mechanistic basis of ageing. I then explore how diet affects lifespan and reproduction in either sex. Finally, I test the hypotheses that oxidative stress, which occurs when cellular levels of Reactive Oxygen Species exceed circulating antioxidant defences causes ageing (i.e. the free radical theory of ageing) and/or constrains life-history strategies. To ask these questions, I employ quantitative genetics in decorated crickets Gryllodes sigillatus to examine the genetic co(variance) of ageing, lifespan, reproductive effort, oxidative damage and antioxidant protection. In the Australian field cricket, Teleogryllus commodus, I apply the geometric framework of nutrition to examine how lifespan, reproductive effort, oxidative damage and antioxidant capacity respond to dietary manipulation. In G. sigillatus, I found that sexual selection caused divergent strategies of age-dependent reproductive effort across the sexes and that this, in turn, promoted different rates of ageing in males and females. I found a trade-off between early reproductive effort and ageing rate in both sexes, although this trade-off was more pronounced in females (Chapter 3). I then explored the mechanistic basis of these sex-specific life-history strategies and, in support of the free radical theory of ageing, I found that oxidative damage was greatest in the shortest lived sex (females) and was negatively genetically correlated with lifespan. Additionally, oxidative damage was a cost of female reproductive effort that accelerated ageing, showing that oxidative stress may mediate sex-specific life-history strategies in decorated crickets (Chapter 4). If sexual selection affects reproduction and lifespan it should promote sex-specific life-history responses to dietary manipulation. In Australian black field crickets Teleogryllus commodus, I found that males and females have distinct dietary optima for lifespan and reproductive effort and that diet mediated a trade-off between these traits. I found that mating affected responses to dietary manipulation and caused sexual dimorphism in dietary intake under choice (Chapter 5). However, oxidative stress did not explain these life-history responses to dietary manipulation across the sexes (Chapter 6): although oxidative damage was greatest in the shortest lived sex (i.e. females), diets that extended lifespan did not reduce oxidative damage. My thesis illustrates the importance of considering sexual selection when considering the evolution and mechanistic basis of ageing. It offers equivocal support for the free radical theory of ageing but shows that oxidative stress may help underpin sex-specific life-history strategies. However, my results highlight that unravelling the relationship between oxidative stress and life-history strategies across the sexes will be a very difficult task.

Barriers to interbreeding limit gene flow between sister taxa, leading to reproductive isolation and the maintenance of distinct species. These barriers come in many forms, and can act at different stages in the reproductive process. Pre-copulatory barriers may be due to individuals discriminating against heterospecifics in mate choice decisions. These decisions may be informed through a range of sensory modalities. If a female is mated and inseminated, then there may be multiple postmating-prezygotic barriers that affect the success of heterospecific sperm in attaining fertilisations. Post-zygotic barriers can be very early acting, resulting in embryonic fatality, or may be later acting, affecting the fitness of hybrid offspring. In this thesis I investigate potential reproductive barriers between the interbreeding field crickets Gryllus bimaculatus and G. campestris. I find that females of both species show only weak preference for conspecific calling song, and may even respond phonotactically to songs typical of heterospecific males. Female G. bimaculatus are repeatable in their preferences and strength of response. G. bimaculatus females presented with synthetic songs prefer those with longer inter-pulse intervals, whereas G. campestris show no discrimination between these songs. Upon meeting, G. campestris females strongly discriminate against heterospecific males, behaving aggressively towards them. This is likely driven by females responding to close range species recognition cues, including chemoreception. The species differ in their cuticular hydrocarbon profiles, and females that are no longer able to use their antennae to receive chemosensory information reduced their aggressive behaviour towards heterospecific males. G. bimaculatus females will mate with heterospecific males, though less readily than to conspecifics. When sequentially mated to both conspecific and heterospecific males, these females will preferentially take up and store sperm from the conspecific male, and sperm from conspecific males is more likely to sire offspring than would be predicted from the proportion of sperm in storage. Eggs from inter-species mating pairs are less likely to begin embryogenesis, and are more likely to suffer developmental arrest during the early stages of embryogenesis. However hybrid embryos that survive to later stages of development have hatching success similar to that of pure-bred embryos. After mating, phonotaxis of G. bimaculatus females towards male songs follows a pattern of suppression and subsequent recovery, likely triggered through detection of seminal proteins transferred in the male ejaculate, or detection of mechanical filling of the spermatheca. This pattern of suppression and recovery of phonotaxis does not differ between females mated to conspecific or heterospecific males. Females that lay few or no eggs do not experience a refractory period.

Existing studies have demonstrated that choosing a partner is strongly determined by physical and personal characteristics of a parent of the opposite sex. This influence is affected by the quality of the relationship with the parent during one's childhood. There are many studies focused on choosing a partner in relation to self-similarity. They show that many characteristics are shared between partners. The partner self-similarity has a positive impact on one's satisfaction in and stability of a relationship. Previous research also shows consistency in choosing a partner, meaning there exists a resemblance among ex-partners. The main objective of this thesis is to make a contribution to understanding the mechanisms of choosing a partner based on similarity (colour of eyes and hair) with the parent of the opposite sex and/or based on self-similarity. Next aim is to explore consistency in choosing a partner according to phenotype characteristics (eye and hair colour). The online survey involved overall 1 266 participants, 942 women and 324 men. The survey provided following results. Women choose self-similar partners in terms of eye colour; they also choose their partners depending on the eye colour of their father. Those women with hair colour similar to their partner's show higher relationship...

Sexual interactions play an important role in generating sexual selection and antagonistic co-evolution. These forces can shape differences between the sexes, but also have the potential to generate population divergence and contribute to speciation. The aim in this thesis was to provide new insights into the genes involved in different stages of female sexual interactions, using Drosophila as a model system. In chapter 2 I tested whether a candidate gene (period) that influences species-specific rhythmic characteristics in male courtship song in D. melanogaster also has a pleiotropic effect on female song preference. Using mutant and transgenic strains I found support for this. In chapter 3 I examined further how females respond to the song at the level of gene expression, using microarrays. Expression profiles revealed modest changes in transcripts abundance overall, which were dominated by antennal olfactory genes, neuropeptide encoding genes and immunity genes. Many of these have previously been found to respond to mating. In chapter 4 I therefore studied further two of these genes, TurandotM and TurandotC and their role in female post-mating fitness. Using RNA interference I found that knocking down these genes influenced immediate fecundity. In chapter 5 I focused on analysing post-mating gene expression patterns in relation to sexual selection in D. pseudoobscura using microarrays. I explored the consequences of experimental variation in female promiscuity on gene expression divergence as a whole, and in response to mating. I found large-scale expression divergence between monandrous and polyandrous females after 100 generations of experimental evolution. Experimental polyandry increased the expression of genes that show female-biased expression in wild-type individuals and decreased male- biased gene expression. Females experiencing no sexual selection showed the opposite pattern. Out of the genes affected by mating, the majority showed increased expression in polyandrous compared to monandrous females, with enrichment e.g. in oogenesis-related genes.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg in fulfillment of the requirement for the degree of Doctor of Philosophy JOHANNESBURG January 1996 / I investigated some evolutionary implications of female mate choice in a feral population of guppies (Poecllia reticultuai. I performed correlative and manipulative experiments to establish the relationship between female mate choice and other sexually selective forces including iutermale aggression and sneak copulation, and the exaggerated secondary sex characters (ornaments) of male guppies. Orange (carotenoid) ornamentation is the best predictor of male attractiveness and mating success, a relationship which held under manipulation. Black (melanin) is sometimes correlated with male mating success. Mnnipulatiug the black area of males reveals that it is important to male attractiveness, and this appears to be in the form of a signal amplifier of male orangeness. This is the fi.st experimental evidence for a visual signal amplifier. For both orange and black areas, the relationship between absolute area and fluctuating asymmetry is positive and significant, suggesting that neither is n signal of male condition. These results arc Interpreted in the context of theories of the evolution of multiple male ornaments. Females are able to express their preference for orange with the first mature male they ever encounter, uuggestlng an important role for genetic determination in female preferences. This is corroborated by high repeatability of female mate choice behaviour. Experience modifies a female's preferences as she is able to adjust her response to a male in relation to the ornamentation of (at least) the previous male she saw. Mate copying has no mensurable effect on the outcome of female mate choice decisions. / MT2016

Although sexual selection in nature has been studied intensively, much is still unknown about the evolution of mating systems in wild populations: for example, how male competition and female choice interact, or the effect of environmental heterogeneity on selection. Further, important questions remain about the consequences of sexual selection for genetic structuring and genetic variation within populations. In this thesis, I investigate the causes and consequences of sexual selection in a polygynous mammal, the red deer Cervus elaphus. This species is characterized by high male reproductive skew resulting from competition to defend harems of females. Here however, I present evidence for previously unappreciated complexity in the mating system, in terms of female mating behaviour and environmental influences on male-male competition. I then go on to investigate the consequences of non-random mating on co-ancestry and inbreeding in the population. Finally, I investigate methods for separating genetic and environmental sources of covariance between individuals. Specifically, I: (i) Show a surprising degree of female mobility during the breeding season (the 'rut‘). Around 40% of females change harem when in oestrus and almost half of these movements result in paternity for the novel male; however I show that these movements are unlikely to be explained by female choice for mates. (ii) Reveal that variance in male mating success is affected by variation in ecological parameters, in particular the interaction between the number of immigrant males in the rutting population and the temporal synchrony of females. (iii) Demonstrate substantial inter-individual differences in the plasticity of acoustic signals produced by rutting males with changes in social context. (iv) Reveal the existence in this population of three rarely reported mating behaviours in polygynous mammals. I find around a fifth of females mate with the same male in multiple years; female relatives frequently mate with the same male; and males rut in locations close to their relatives. Further, I show these behaviours are associated with higher co-ancestry and inbreeding in the population than expected under random mating. (v) Finally, I investigate how spatial associations between relatives upwardly bias estimates of heritability in four phenotypic traits. I do this by accounting for shared environment effects in animal models by i) inclusion of spatial autocorrelation parameters and ii) a novel multi-matrix approach.

Animals’ personality traits are defined as consistent behavior tendencies and the function of them in life-history strategy and reproductive success has been given a lot of explanations in a large amount of research. However, the behavior consistency of individuals in different sexes, mating status and selection regimes is rarely mentioned. In this research, we were interested in personality traits and their consistency in inter-individuals and intra-individuals, and proposed that with the removal of fecundity selection males would evolve to be more female-like and decrease their locomotor activity, and copulation would change the physiological status of females and thus alter their levels of activity.   In the experiment, seed beetles (Callosobruchus maculatus) that were artificially selected in monogamy, polygamy and male-limited selection regimes were weighed, dropped in a designed arena and their behaviors were recorded with a camera for four minutes in the first day when they were newborn and virgin. In the next day, the virgin beetles were randomly paired to mate, weighed afterwards, and dropped in the arena again for videoing the same setting as yesterday. In data collection step, with these videos four behaviors types including walking, entering squares, time spent on roof and entering a new area were observed, scored and noted down. To process the data, we made correlation analysis and it was found that walking, entering square and a new area were positively correlated. After building the linear mixed effect models we found that sex together with mating significantly act in modifying beetles’ behaviors, males were more active than females but the difference was narrowed after mating, and copulation caused a significant increase in the level of locomotor activity in females. To our disappointment, selection regimes did not have any significant impact on locomotor activity. Our work gave an insight that copulation changed individuals’ behaviors more in females than in males and dimorphic expression of sex-biased genes differed due to mating effect.