Sexual reproduction entails complex co-evolution between the sexes, necessary for successful fertilization, ensuring individual and population-level fitness. Interfertility is the main criterion for species definition and understanding speciation requires detailed studies of reproductive barriers. However, many studies on reproductive barriers are constrained to infer evolutionary processes from patterns. In this thesis, I focus on a hybrid zone between collared and pied flycatchers (Ficedula albicollis and hypoleuca) on the island of Öland, and a trait that is essential for fertilization: sperm. Long-term monitoring of these species, combined with recent advances in molecular tools, allow me to study how complex on-going intersexual and interspecific interactions influence reproductive isolation in this young hybrid zone. I start by exploring the links between pre- and postmating sexual selection within collared flycatchers (paper I and II). I show that secondary sexual characters and indirect mate-choice benefits are tightly linked to physiology (paper I), and that a male’s attractiveness and dominance status dictate which sperm traits are optimal, as a male’s fertilization success depends on an interaction between sperm and display traits (paper II). I then report a source of strong postzygotic isolation between recently diverged collared and pied flycatchers: impaired spermatogenesis resulting in absence of mature sperm cells in hybrid males (paper III). I show however that pied flycatcher females, who are most exposed to hybridization, can mitigate these costs through mechanisms of cryptic female choice impairing heterospecific sperm performance, allowing them to bias paternity towards pure-species offspring (paper IV). Finally, by exploring the testes transcriptomes and sperm proteomes of both species, I highlight the importance of gene and protein regulation mechanisms in facilitating phenotypic divergence between these species (paper V). Thus, my thesis reveals complex interactions between primary and secondary sexual characters in a wild bird and suggests that mechanisms of sexual selection are tightly linked to essential physiological functions. I also show that genetic incompatibilities can evolve rapidly despite low genome-wide levels of divergence but that divergence in regulatory regions and proteins potentially allows fast evolution of molecular mechanisms impairing or preventing costly heterospecific fertilization.

Doctor of Philosophy / Department of Biology / Brett K. Sandercock / Sexual selection via female choice and male-male aggression leads to elaboration of male traits. If male traits correlated with reproductive success are honest signals of male quality, survival costs may be associated with the expression of those traits. Testosterone (hereafter ‘T’) may enhance male breeding success, but T can also reduce immunocompetence and survival. Socially monogamous male birds with higher circulating T experience reproductive advantages, but the role of T in lek mating systems is largely unknown. To address these issues, I individually marked and conducted focal behavioral observations of greater prairie-chickens (Tympanuchus cupido) at five lek sites over a 5-year period. Females were fitted with radio-telemetry to monitor nesting success and survival. I examined the relationship between male traits and mating success using multinomial discrete choice models, a statistical method not previously applied to studies of sexual selection. Male mating success was highly skewed at greater prairie-chicken leks with 18.5% of males obtaining 87.2% of all successful copulations (n = 108 males; 85 copulations). Mating success was influenced most by male behavior, followed by several morphological attributes. The role of T was quantified using blood samples and by experimentally implanting a subset of males with T. T did not consistently affect mating success. Non-territorial males had lower T levels than territorial males. Among territory holders, T was unexpectedly negatively correlated with mating success. However, the odds of receiving a copulation were 4.3 times (0.42 to 45.3) greater for T-implanted males than males with sham implants. Future work should explore the interactions among the immune system, parasite load, and mating success of prairie-chickens. Annual survival of male prairie-chickens was not related to mating success, behavior, age or T level, suggesting there is no cost of increased male mating success. Like males, reproductive success of females was also highly skewed because < 10% of nests successfully hatched young. Comparisons of seasonal and annual survival rates indicate that females experience increased mortality during the breeding season relative to the nonbreeding season. Synthesis of field estimates of demographic parameters indicates prairie-chicken populations will decline without changes in rangeland management to reduce predator numbers or provide more nesting cover.

The work included in this thesis aims at exploring the environmental sensitivity of benefits and costs of sexual selection through a combined empirical and theoretical effort, to increase our understanding of the impact of environmental change on sexually reproducing populations.Can sexual selection promote adaptation to novel environments? Sexual selection for good genes should accelerate adaptation by granting higher reproductive success to individuals of high genetic quality. However, sexual conflict is a frequent outcome of sexual reproduction and may often be detrimental to population fitness. Experimental evolution has shown that the role of sexual selection in adaptation is variable, because of a complex balance between the detrimental and beneficial effects described above.The present thesis is investigating the role of sexual selection in adaptation by focusing on the sex-specific strength of selection and the intensity of intralocus sexual conflict (IaSC) in ancestral and novel environments. The sex-specific strength of selection is a valuable proxy for the benefits of sexual reproduction, since a male-bias in selection caused by sexual selection should allow efficient purging of deleterious alleles with little impact on female fecundity and cost to population fitness.This thesis investigates both sex-specific selection and IaSC across benign and novel environments in two species of seed beetles, Callosobruchus maculatus and Acanthoscelides obtectus, and includes a theoretical model of the effect of environmental change on of sexual selection. The empirical part of my results indicates that, generally, selection at the adult stage is male biased but that this male bias may be reduced under stress, pointing towards reduced benefits of sexual selection under rapid environmental change. Additional simulations suggest that the frequency dependent nature of sexual selection alone could explain this trend. No empirical support was found for the reduction of IaSC under stress.It is becoming crucial today to understand the impact of environmental change on natural populations. This thesis brings new material adding to our understanding of the role of sexual selection within that particular issue. The outcome of sexual selection is dependent on a variety of mechanisms, such as good genes processes and sexual conflict, which are very likely to be dependent on ecological factors and specificity of the system studied. For that reason, carefully controlled experiments on laboratory systems and mathematical modelling are necessary steps that should ultimately lead to the study of similar questions in natural systems.

Directional selection is prevalent in nature yet phenotypes tend to remain relatively constant, suggesting a limit to trait evolution. The genetic basis of evolutionary limits in unmanipulated populations, however, is generally not known. Given widespread pleiotropy, opposing selection on a focal trait may arise from the effects of the underlying alleles on other fitness components, generating net stabilizing selection on trait genetic variance and thus limiting evolution. Here, I look for the signature of stabilizing selection for a suite of cuticular hydrocarbons (CHCs) in Drosophila serrata. Despite strong directional sexual selection on CHCs, genetic variance differed between high and low fitness individuals and was greater among the low fitness males for seven of eight CHCs. Univariate tests of a difference in genetic variance were non-significant but have low power. My results implicate stabilizing selection, arising through pleiotropy, in generating a genetic limit to the evolution of CHCs in this species.

Among multi-male, multi-female primate groups, males engage in direct contest competition for access to mates. The priority-of-access model (PoA model) generally predicts that male reproductive success increases with male dominance rank, but the strength of this relationship is expected to decrease with increasing female reproductive synchrony, particularly in seasonally breeding primates. Genetic paternity studies support the model’s predictions, having found a positive relationship between male dominance rank and reproductive success. However, in addition to dominance status and female reproductive synchrony, a number of proximate factors also impact males’ ability to sire offspring, which have not been considered in studies of male reproductive strategies.By integrating behavioral, genetic, morphological, and hormonal analysis as more direct measures of reproductive success in individual males, this dissertation investigated the relationship between male dominance rank and reproductive success and including the proximate factors affecting this relationship in wild northern pig-tailed macaques (Macaca leonina). The main objectives of this study are: 1) to identify the relationships between male dominance rank, male mating success, and male reproductive success, and assess to what extent female synchrony affects these relationships; 2) to identify the proximate factors that may reduce the reproductive success of the top-ranking male and assess variation in male mating tactics related to dominance rank and migration status (i.e., resident males vs. extra-group males); and 3) to evaluate the function of males’ red ornaments that may be used to signal male dominance status (male-male competition) to attract females (female mate choice) or both. The study was conducted at Khao Yai National Park, northeastern Thailand. Systematic data collection on CH group occurred from September 2015-June 2017. The group composition was recorded daily as well as births, deaths, individual emigrations and immigrations, females’ parity status, and the presence of extra-group males (EGMs). Sociosexual data and male-female interactions (i.e., copulations, ejaculatory copulations, consortships, grooming, female proceptive behaviors and receptive behaviors) were recorded during females’ receptive periods. To assess male reproductive success, genetic paternity analyses were conducted on fecal DNA samples collected from 18 adult and subadult males, 22 adult females, and 25 juveniles and infants. To measure red skin coloration of males, hindquarter images were collected non-invasively for seven adult males. From those images, skin color and luminance were computationally quantified to assess variation in male anogenital reflectance. Lastly, fecal samples were collected from nine adult males to assess monthly levels of fecal testosterone by microtitreplate enzyme immunoassay. The distribution of births and matings suggested that northern pig-tailed macaques, at least in this group, are best categorized as moderate seasonal breeders. Indeed, 33-67% of births occurred within a three-month period. Copulation data revealed a positive relationship between male dominance rank and mating success, supporting the predictions of the PoA model. However, the distribution of male reproductive success indicated that: 1) high-ranking males controlled a proportion of paternity much lower than predicted by the PoA model; 2) middle-ranking males controlled a proportion of paternity higher than predicted by the model; and 3) EGMs, not considered in the PoA model, controlled a surprisingly large proportion of paternity despite a low observed mating success. When females were simultaneously receptive, lower-ranking and subadult males engaged in opportunistic and surreptitious copulation and avoided direct competition with higher-ranking males, and most females approached and mated with EGMs out of the resident adult males’ sight. However, one EGM also mated in full sight of resident adult males. This is the first study to report mating and successful paternity by EGMs in a moderately seasonally breeding species.Four male mating tactics were identified: 1) the top-ranking resident male tactic, in which the male competes for the alpha male position to control priority of access to receptive females through long consortships and copulations; 2) the lower-ranking resident male tactic, in which the male copulates opportunistically and surreptitiously out of sight of higher-ranking males mostly during the mating peak; 3) the subordinate EGM tactic, in which the male lives semi-solitarily and copulates opportunistically and surreptitiously, mostly during the mating peaks; and 4) the super-dominant EGM tactic, in which the EGM copulates irrespective of the presence of other males and in full sight of even the highest-ranking resident male. In addition, I found support for female mate choice. Darker and redder males had more mating partners, received more female proceptive behaviors, and were engaged in more consortships and grooming with receptive females. Furthermore, males became redder and darker as female reproductive synchrony increased. Together, these results suggest that male red ornaments exhibited in the male’s anogenital area is attractive to females. Furthermore, behavioral evidence of female mate choice towards EGMs was found. This dissertation provides a comprehensive picture of the complex male mating tactics of northern pig-tailed macaques. To achieve reproductive success, males engage in a diversity of mating tactics, strongly influenced by male dominance rank and the degree of female reproductive synchrony. However, mate-guarding costs, surreptitious copulations by lower-ranking males and EGMs, and female mate choice, need to be included in an extended version of the PoA model to provide stronger predictions of the distribution of male reproductive success in primates.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第21605号 / 理博第4512号 / 新制||理||1647(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 朝倉 彰, 准教授 下村 通誉, 教授 中務 真人 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

In dense mating aggregations, such as insect and anuran choruses, signals produced at the same time can overlap and interfere with one another, reducing the ability of receivers to discriminate between individual signals. Thus, evolution by sexual selection is expected to result in mating signal timing strategies that avoid overlap. Patterns of signal alternation between competing males are commonly observed in leks and choruses across taxa. In some species, however, signalers instead deliberately overlap, or ‘synchronize’, their mating signals with neighboring conspecifics. Given the assumed high cost of reduced mate attraction when signals overlap, mating signal synchronization has remained an evolutionary puzzle. Synchronization may be beneficial, however, if overlapping signals reduce the attraction of nontarget receivers (predator avoidance hypothesis). Synchronized signals could also constructively interfere, increasing female attraction to the mating aggregation (the beacon effect hypothesis). I investigate these functions of synchronized signaling in two species of tree frogs that synchronize their mating calls: the pug-nosed tree frog (<i>Smilisca sila</i>) and the Ryukyu Kajika frog (<i>Buergeria japonica</i>). To examine the trade-offs imposed by call synchronization in each species, I conduct a series of field and laboratory playback experiments on target (female frogs) and nontarget (eavesdropping predators) receivers of frog calls. Results from these experiments support both hypotheses, suggesting that synchronized frog calls can reduce the attraction of predators and attract mates to the chorus. In addition, I found reduced preferences for fine-scale call timings in female <i>S. sila</i> and <i>B. japonica</i>, deviating from the expected preferences observed in many other anuran and non-anuran species. Thus, while males may enjoy multiple benefits from synchronized mating signals, relaxed sexual selection for non-synchronous signals may be key to the evolution and maintenance of mating signal synchrony.

Sexual selection theory tries to explain evolution of apparently useless traits which mainly developed in males of numerous species. One such trait is also rich and vibrant coloration, typical for many of the bird species. These traits are difficult to be falsified, and therefore they honestly signal quality of the individual. Carotenoid coloration reflects the health condition and melanin coloration the social status, even though this traditional division might not be as strict according to the latest studies. Apart from these ways of maintaining honesty, recent studies are focusing more also on the effect of hormones, mainly two steroids: male sexual hormone - testosterone -, and the "stress" hormone - corticosterone. Both hormones could positively influence male's sexual traits such as ornamental coloration. On the other hand, elevated levels of these hormones possess risk to the organism (higher energetic expenditure, chronic stress), therefore also might potentially become costly. Using photographs of birds in standardized conditions as well as spectrophotometry I analyzed the plumage coloration of males of the Yellowhammer (Emberiza citrinella). Concentrations of testosterone and corticosterone deposited in feathers were analyzed using the LC-MS/MS. Also, for males in breeding season 2015,...

Like many other animals, butterflies are able to visually perceive the ultraviolet (UV) light; many species even have patterns on their wings which are visible in this part of the electromagnetic spectrum. Over the last forty years, it has been shown that these UV patterns play an important role in behaviour of many butterflies, especially in relation to sexual selection - they are involved in the process of recognising a suitable mate, and likely can signal some of the mate's qualities, such as its age, ability to handle stressful environmental factors, or efficiency in foraging. The patterns may also be used for taxonomical purposes. This dissertation thesis contains a comprehensive research into ultraviolet patterns of the Gonepteryx brimstones, with a primary focus on the issue of environmental influences in relation to the expression of these traits, on the patterns' potential role in sexual selection, or on their evolution. It has been successfully demonstrated that UV patterns of at least some Gonepteryx species are affected by the environment to a strong degree, significantly more than the traits not involved in sexual selection. On the whole, the conclusions made by submitted publications suggest that UV patterns play a role in the sexual selection of the chosen brimstones, though it is not clear...

Flower chafers are well-known beetles with apparent sexual dimorphism. Yet, in contrast to other groups of scarab beetles, only little attention has been paid to various aspects of this phenomenon. It concerns also sexual dimorphism in size, which is very common in animals. Although ultimate causes of sexual size dimorphism have been extensively studied, the developmental mechanisms are still only poorly understood. We investigated proximate causes of sexual size dimorphism in several differentially dimorphic flower chafer species. We found that in highly dimorphic species the dimorphism started to develop already in the first instar and tended to accumulate through successive larval development. In contrast, the sexes in species with a relatively low dimorphism diverged in size during only one instar. Moreover, we found variability not only in when the dimorphism arises during development, but also how: sex-related differences in both the instar duration and average growth rate were the proximate causes of sexual size dimorphism. In addition, we showed that the sexes may differ also in growth trajectory - males had relatively longer period of rapid growth than females, even in cases where the absolute development times were similar in both sexes. Further, we focused on systematic survey of sexual...