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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.

<p>Sexual selection arises through variation in reproductive success. This thesis investigates different aspects important in sexual selection, namely nest building, sperm competition, paternity and paternal care, and their mutual interrelationships. In the studied species, the sand goby (<i>Pomatoschistus minutus</i>) and the common goby (<i>Pomatoschistus microps</i>), sperm competition did arise when small males, so called sneakers, sneaked into other males nests and released sperm. They seemed to use female behaviour as their prime cue for a sneaking opportunity. However, also nest-holders, both with and without eggs, were found to fertilize eggs in the nests of other males.</p><p>Clearly, nest-holding males tried to prevent other males from spreading their sperm in their nests, since they showed aggression towards such males. A nest building experiment indicated that the small nest-openings found in the sneaker male treatment were sexually selected through protection against sneaking or by female choice. Yet, no behavioural or genetical support for the hypothesis that the nest functions as a physical or visual defence, or that sneaker males prefer to sneak upon nests with wide nest-openings, were found in the other studies. Still, individual nest-holding males showed a higher mucus preparation effort inside the nest in the presence of a sneaker male than when alone. In close relatives, such mucus contains sperm, suggesting an importance in sperm competition. However, the mucus may also have pheromone and anti-bacterial functions and may constitute a mating effort, as found in other gobies. Both a behavioural and a mate choice experiment suggested that the males were not less eager to spawn in the presence of a sneaker male.</p><p>Sneak intrusion did not affect nest defence, fanning or filial cannibalism, nor had paternity an effect on filial cannibalism. This and various life history aspects, together with the fact that the parasitic male only fertilized a fraction of the clutches, would predict females to ignore sneaker males. This was also the case, as the presence of sneaker males was found not to affect female spawning decision. Still, several females spawned in two nests, which coincided with parasitic spawnings, suggesting a cost of disturbance for the females and thus a substantial cost to the nest-holding males in terms of lost mating success. However, females paid attention to other traits in their choice of mate since spawning was associated with sand volume of the nest, but not with nest-opening width. Also, female (but not male) courtship was correlated with partial clutch filial cannibalism, indicating that females are able to anticipate future male cannibalism.</p><p>In a partial correlation of nest opening, sand volume, male courtship display, displacement fanning and male size, a large number of traits were correlated both positively and negatively with regard to how we may expect them to be appreciated by females. For instance, males which fan well also build large nests or display intensely (but not both). Together with all the other results of this thesis, this shows the entangled selection pressures working on breeding animals, as well as the different male and female tactics employed to maximize their reproduction.</p>

<p>Multiple mating by females is common in nature. Yet, the evolution and maintenance of polyandry remains a bit of an evolutionary puzzle. It was my aim in this thesis to reach a greater understanding of this phenomenon as well as to investigate the consequences of polyandry on the evolution of reproductive divergence in insects. In an extensive meta analysis addressing the direct effects of multiple mating on female fitness in insects, I found that insects gain from multiple matings in terms of increased lifetime offspring production. In species without nuptial feeding, increased mating rate leads to decreased female lifespan and my results strongly support the existence of an intermediate optimal female mating rate. However, results from an experimental study where I examined the relationship between female fitness and mating rate in the bean weevil (Callosobruchus maculatus) showed that female fitness was maximized at two alternative mating rates, indicating that some species may exhibit a more complex relationship between the costs and benefits of mating. In the meta analysis on species with nuptial feeding, I found only positive effects of increased mating rate and the puzzle is rather what constrains the actual mating rates of females in these groups.</p><p>Sexual selection is a very potent driver of rapid evolutionary change in reproductive characters. Most research has focussed on precopulatory sexual selection, but in promiscuous species sexual selection continues after copulation and variance in male fertilization success gives rise to postcopulatory sexual selection. In this thesis I found that three allopatric populations of the red flour beetle (Tribolium castaneum) have diverged in traits related to reproduction. Male genotype affected all aspects of female reproduction, but more interestingly, males and females interacted in their effect on offspring production and reproductive rate, showing that the divergence was due to the evolution of both male and female reproductive traits.</p><p>When studying postcopulatory sexual selection, sperm competition has been put forward as the main source of variance in fertilization success. The results from a set of double-mating experiments, using the same populations of flour beetles, provided strong evidence that cryptic female choice is also important in generating variance in male fertilization success. I found not only main effects of female genotype on male fertilization success but also male-female interactions which provide more unambiguous evidence for cryptic female choice. Finally, I attempted to uncover which male signals-female receptors are involved in the reproductive divergence observed in the Tribolium populations. In a double-mating experiment I manipulated female perception of two male reproductive signals, copulatory courtship and cuticular hydrocarbons, and the results indicate that, within populations, both signals are sexually selected. However, only male cuticular hydrocarbons seem to be involved in the reproductive divergence between the populations. </p><p>In conclusion, multiple mating by female insects can be understood solely in terms of direct fitness benefits resulting from increased offspring production. I have shown that postcopulatory sexual selection can lead to rapid divergence in reproductive traits related to mating and that cryptic female choice plays an important role in this divergence.</p>

<p>The importance of cryptic female choice, i.e. female post-copulatory influence over male reproductive success, in driving the evolution of male traits remains controversial. The main aim of this thesis was to understand the post-copulatory consequences of sexual interactions and the importance of cryptic female choice in two species of beetle.</p><p>Males of the red flour beetle Tribolium castaneum use their legs to rub the lateral edges of the female elytra during mating. When manipulating female perception of this behaviour, I found that females preferentially use the sperm of males with vigorous leg rubbing when they mate with more than one male. Leg rubbing also appeared to increase female rate of oviposition. Females do not seem to gain any indirect benefits by preferring males with an intense leg rubbing behaviour since this behaviour was found to have very low narrow sense heritability and did not appear to be condition dependent in its expression.</p><p>Males of the bruchid beetle Callosobruchus maculatus have spiny genitalia that harm their mates. Females kick males during copulation and when prevented from kicking, suffered reduced lifetime offspring production as a consequence of more extensive injuries. Males were not able to delay female remating, increase rate of oviposition or increase sperm precedence by inflicting relatively severe injuries to non-kicking females. Hence, the injuries appear to be side effects of male efforts to remain in copula. When copulation duration was manipulated, ejaculate size and female lifetime offspring production increased with the length of copulation. Females reduced their mating rate when they had access to water, suggesting that they obtain water from the large ejaculates and trade-off their need for additional water against the costs of mating. Males may then reduce the benefits of remating by providing their mates with a large amount of water. Females did not increase their remating propensity to avoid inbreeding when they had mated to brothers. Together, these studies reveal the complexity of sexual interactions and the importance of post-copulatory processes for the fitness of both males and females.</p>

Multiple mating by females is common in nature. Yet, the evolution and maintenance of polyandry remains a bit of an evolutionary puzzle. It was my aim in this thesis to reach a greater understanding of this phenomenon as well as to investigate the consequences of polyandry on the evolution of reproductive divergence in insects. In an extensive meta analysis addressing the direct effects of multiple mating on female fitness in insects, I found that insects gain from multiple matings in terms of increased lifetime offspring production. In species without nuptial feeding, increased mating rate leads to decreased female lifespan and my results strongly support the existence of an intermediate optimal female mating rate. However, results from an experimental study where I examined the relationship between female fitness and mating rate in the bean weevil (Callosobruchus maculatus) showed that female fitness was maximized at two alternative mating rates, indicating that some species may exhibit a more complex relationship between the costs and benefits of mating. In the meta analysis on species with nuptial feeding, I found only positive effects of increased mating rate and the puzzle is rather what constrains the actual mating rates of females in these groups. Sexual selection is a very potent driver of rapid evolutionary change in reproductive characters. Most research has focussed on precopulatory sexual selection, but in promiscuous species sexual selection continues after copulation and variance in male fertilization success gives rise to postcopulatory sexual selection. In this thesis I found that three allopatric populations of the red flour beetle (Tribolium castaneum) have diverged in traits related to reproduction. Male genotype affected all aspects of female reproduction, but more interestingly, males and females interacted in their effect on offspring production and reproductive rate, showing that the divergence was due to the evolution of both male and female reproductive traits. When studying postcopulatory sexual selection, sperm competition has been put forward as the main source of variance in fertilization success. The results from a set of double-mating experiments, using the same populations of flour beetles, provided strong evidence that cryptic female choice is also important in generating variance in male fertilization success. I found not only main effects of female genotype on male fertilization success but also male-female interactions which provide more unambiguous evidence for cryptic female choice. Finally, I attempted to uncover which male signals-female receptors are involved in the reproductive divergence observed in the Tribolium populations. In a double-mating experiment I manipulated female perception of two male reproductive signals, copulatory courtship and cuticular hydrocarbons, and the results indicate that, within populations, both signals are sexually selected. However, only male cuticular hydrocarbons seem to be involved in the reproductive divergence between the populations. In conclusion, multiple mating by female insects can be understood solely in terms of direct fitness benefits resulting from increased offspring production. I have shown that postcopulatory sexual selection can lead to rapid divergence in reproductive traits related to mating and that cryptic female choice plays an important role in this divergence.

Sexual selection arises through variation in reproductive success. This thesis investigates different aspects important in sexual selection, namely nest building, sperm competition, paternity and paternal care, and their mutual interrelationships. In the studied species, the sand goby (Pomatoschistus minutus) and the common goby (Pomatoschistus microps), sperm competition did arise when small males, so called sneakers, sneaked into other males nests and released sperm. They seemed to use female behaviour as their prime cue for a sneaking opportunity. However, also nest-holders, both with and without eggs, were found to fertilize eggs in the nests of other males. Clearly, nest-holding males tried to prevent other males from spreading their sperm in their nests, since they showed aggression towards such males. A nest building experiment indicated that the small nest-openings found in the sneaker male treatment were sexually selected through protection against sneaking or by female choice. Yet, no behavioural or genetical support for the hypothesis that the nest functions as a physical or visual defence, or that sneaker males prefer to sneak upon nests with wide nest-openings, were found in the other studies. Still, individual nest-holding males showed a higher mucus preparation effort inside the nest in the presence of a sneaker male than when alone. In close relatives, such mucus contains sperm, suggesting an importance in sperm competition. However, the mucus may also have pheromone and anti-bacterial functions and may constitute a mating effort, as found in other gobies. Both a behavioural and a mate choice experiment suggested that the males were not less eager to spawn in the presence of a sneaker male. Sneak intrusion did not affect nest defence, fanning or filial cannibalism, nor had paternity an effect on filial cannibalism. This and various life history aspects, together with the fact that the parasitic male only fertilized a fraction of the clutches, would predict females to ignore sneaker males. This was also the case, as the presence of sneaker males was found not to affect female spawning decision. Still, several females spawned in two nests, which coincided with parasitic spawnings, suggesting a cost of disturbance for the females and thus a substantial cost to the nest-holding males in terms of lost mating success. However, females paid attention to other traits in their choice of mate since spawning was associated with sand volume of the nest, but not with nest-opening width. Also, female (but not male) courtship was correlated with partial clutch filial cannibalism, indicating that females are able to anticipate future male cannibalism. In a partial correlation of nest opening, sand volume, male courtship display, displacement fanning and male size, a large number of traits were correlated both positively and negatively with regard to how we may expect them to be appreciated by females. For instance, males which fan well also build large nests or display intensely (but not both). Together with all the other results of this thesis, this shows the entangled selection pressures working on breeding animals, as well as the different male and female tactics employed to maximize their reproduction.

The importance of cryptic female choice, i.e. female post-copulatory influence over male reproductive success, in driving the evolution of male traits remains controversial. The main aim of this thesis was to understand the post-copulatory consequences of sexual interactions and the importance of cryptic female choice in two species of beetle. Males of the red flour beetle Tribolium castaneum use their legs to rub the lateral edges of the female elytra during mating. When manipulating female perception of this behaviour, I found that females preferentially use the sperm of males with vigorous leg rubbing when they mate with more than one male. Leg rubbing also appeared to increase female rate of oviposition. Females do not seem to gain any indirect benefits by preferring males with an intense leg rubbing behaviour since this behaviour was found to have very low narrow sense heritability and did not appear to be condition dependent in its expression. Males of the bruchid beetle Callosobruchus maculatus have spiny genitalia that harm their mates. Females kick males during copulation and when prevented from kicking, suffered reduced lifetime offspring production as a consequence of more extensive injuries. Males were not able to delay female remating, increase rate of oviposition or increase sperm precedence by inflicting relatively severe injuries to non-kicking females. Hence, the injuries appear to be side effects of male efforts to remain in copula. When copulation duration was manipulated, ejaculate size and female lifetime offspring production increased with the length of copulation. Females reduced their mating rate when they had access to water, suggesting that they obtain water from the large ejaculates and trade-off their need for additional water against the costs of mating. Males may then reduce the benefits of remating by providing their mates with a large amount of water. Females did not increase their remating propensity to avoid inbreeding when they had mated to brothers. Together, these studies reveal the complexity of sexual interactions and the importance of post-copulatory processes for the fitness of both males and females.

Thesis (Ph. D.)--Miami University, Dept. of Zoology, 2003. / Title from second page of PDF document. Includes bibliographical references.