In this dissertation, I report new information that is necessary for future mating system studies in a little studied species, the marbled salamander (Ambystoma opacum). I studied female mating behavior, sexual selection, and the consequences of polyandry for individual females and salamander populations. I also compared the performance of several statistical approaches for analyzing genetic mating system data. The first chapter summarizes the characteristics of several novel microsatellite DNA loci as well as cross-amplified loci for marbled salamanders and mole salamanders that may be used for future studies. In the second chapter, I report estimates of sire number for 13 marbled salamander clutches based on microsatellite data from 32 hatchlings per clutch. Females mated with as many as three different males as indicated by conservative techniques. Less than half of females mated with multiple males. Based on comparative analyses, I recommend the parental reconstruction approach with the computer program GERUD for assessing multiple paternity. The third chapter describes an experiment designed to study sexual selection. As expected, in breeding mesocosms, the potential for sexual selection was much higher for males than for females. Size was unrelated to variance in male reproductive fitness. Only opportunity for selection and Morisita’s index conformed to theoretical expectations of the relationship between operational sex ratio and the potential for sexual selection among males. Because opportunity for selection has intuitive links to formal sexual selection theory, I recommend its continued use. In the fourth chapter, I compared polyandrous and monandrous females to explore the potential fitness consequences of multimale mating. No fitness measure at the egg or hatchling stage (clutch size, hatching success, hatchling size, etc.) differed between the two types of clutches. Size of metamorphs was not different, but polyandrous clutches had significantly higher survival to metamorphosis. In the fifth chapter, I analyzed effects of increased polyandry and male availability on genetic diversity, effective population size (Ne), and fitness of experimental populations. Although no analyses were significant, some effects were moderate to high in size. Ne was higher when estimated from hatchlings than with metamorphs.

Nos estudos sobre a teoria da Seleção Sexual, as libélulas têm sido amplamente estudadas devido à grande variedade de padrões comportamentais, de coloração e táticas reprodutivas. Como forma de demonstrar táticas reprodutivas adotadas por duas espécies de libélulas, esta dissertação teve como objetivos principais: i) investigar o papel de traços secundários como a coloração corporal na competição intra-sexual de uma espécie territorial e ii) analisar se os traços corporais como tamanho e morfologia das asas predizem a tática de acasalamento adotada por machos de uma espécie nãoterritorial. Sugere-se que a coloração corporal pode predizer o resultado de lutas e também se correlacionar positivamente com a condição física dos machos territoriais de Tigriagrion aurantinigrum. Ademais, traços corporais como o tamanho e a morfologia das asas influenciam na tática reprodutiva utilizada por machos não-territoriais de Epipleoneura williamsoni. Portanto, com os resultados obtidos, conclui-se que a variação nos sinais visuais exerce um papel essencial na comunicação animal e na resolução de conflitos, indicando ainda que pode haver uma sinalização da condição física dos machos. Além disso, os resultados mostraram evidências em como diferentes táticas reprodutivas se relacionam com traços corporais como agilidade e tamanho corporal, os quais podem influenciar no sucesso reprodutivo dos indivíduos. / In studies concerning Sexual Selection theory, dragonflies and damselflies have been well studied due to their wide range of behavioral, color and reproductive tactics patterns. To demonstrate reproductive tactics adopted by two damselfly species, this study aimed to: i) investigate the role of secondary traits such as body coloration in intrasexual competition of a territorial species and ii) analyze if body traits such as size and wing morphology predicts the adopted tactic by non-territorial males. It is suggested that body coloration can predict the fight outcome and also positively correlates with males physical condition in territorial males of Tigriagrion aurantinigrum and body traits such as body size and wing morphology influence the reproductive tactic adopted by non-territorial males of Epipleoneura williamsoni. Therefore, with these results, it is concluded that the visual signalling variation plays an important role on the animal comunication and conflict resolution, which also may indicate that there is a signalling on the males physical condition. Furthermore, the results showed evidence in how different reproductive tactics are related to body traits such as agility and size, which can influence on individuals reproductive success.

A musicalidade, concebida como o conjunto da capacidade cognitiva subjacente à dança e à comunicação sonora por meio de melodias harmonizadas e ritmadas, satisfaz vários critérios que caracterizam as adaptações biológicas. A música é muito antiga, universal e um importante aspecto em todas as culturas e épocas conhecidas. Ela provoca emoções e reações estéticas fortes, se desenvolve segundo um roteiro ontogenético padrão, envolve uma capacidade neurocognitiva especializada em receber, processar e produzir música, traz benefícios à saúde e apresenta fatores hereditários nas diferenças individuais, consome muita energia e tempo, e tem análogos na sinalização acústica de outras espécies sugerindo homologia e convergência adaptativa. Existem duas principais teorias acerca do valor adaptativo para a musicalidade: coesão grupal e seleção sexual. Elas não são excludentes ou incompatíveis e apresentam muitas sobreposições. Ambas buscam, em diferentes contextos sociais, as pressões seletivas envolvidas na valorização ancestral dos responsáveis pela produção musical e sua apreciação. Entretanto, elas diferem quanto ao grau de diferenças sexuais previsto: a coesão de grupo prevê poucas diferenças sexuais, mas para a seleção sexual as mulheres seriam mais voltadas para apreciação musical, enquanto os homens seriam mais voltados para a exibição musical via instrumento musical. O maior desafio para o enfoque adaptacionista da musicalidade é a ampliação do teste experimental de hipóteses. O objetivo geral desta tese é investigar empiricamente, por meio de diferentes propostas metodológicas, aspectos divergentes e convergentes das influências da seleção sexual e da coesão de grupo na evolução da musicalidade humana integrada às outras artes. Esta tese consiste de quatro estudos que abrangem experimentos naturais e verdadeiros controlados, acessando de forma direta e 13 através de auto-relato tanto a apreciação quanto a produção musical, usando metodologias que requerem a colaboração dos participantes (questionários e gravações do canto), e outras com medidas discretas (como estatísticas oficiais de vestibulares desde 1980), amostrando ampla variedade de cursos de graduação e pós em diferentes regiões do Brasil (São Paulo e Natal) e no exterior (Holanda e Canadá). O conjunto dos resultados revela interculturalmente e temporalmente a existência de diferenças sexuais mais quanto às motivações e disposições para e musicalidade e outras artes do que para capacidades específicas. Os homens são mais voltados para a produção musical instrumental, enquanto as mulheres são mais voltadas para a produção musical cantada, dança, apreciação musical e outras manifestações artísticas. As estratégias sexuais se relacionaram à exibição musical cantada e tocada para os homens, e à importância e apreciação musical para as mulheres. Imaginar-se em um contexto de coesão grupal influencia mais o julgamento dos músicos a partir da música para os homens e num contexto amoroso mais para as mulheres. Ambas, seleção sexual e a coesão de grupo se mostraram inter-relacionadas de novas maneiras. Uma visão ampla e integradora sobre a evolução da musicalidade e das outras artes emergiu do conjunto de resultados e suas implicações / The human musicality, considered as a set of underlying cognitive abilities to dance and sound communication through harmonized rhythmic melodies, meets several criteria which characterize biological adaptations. Music is very old, and an important aspect in all cultures and known past historical periods. It provokes strong emotions and aesthetic responses, it unfolds according to a standard developmental schedule, involves a specialized neurocognitive ability in its perception, processing and production, it gives health and psychological benefits, and there is some hereditary factors on individual differences. It is also very energy-intensive and time consuming, and there are some similarities to the acoustic signalling of other species, suggesting homology and adaptive convergence. There are two main theories about the adaptive values for human musicality, group cohesion and sexual selection. They are not mutually exclusive or incompatible, and exhibit much overlap. Both seek, in different social contexts, the selective pressures involved in the ancestral advantages for music production and appreciation. However, they differ in predictions related to sexual differences: the group cohesion predicts few sex differences, whereas sexual selection predicts that women would be more dedicated to music appreciation, while men would be more focused on displaying via musical instrument. The biggest challenge to the adaptationist approach to musicality is the expansion of the empirical testing of hypotheses. The aim of this thesis is to empirically investigate, using different methodological approaches, divergent and convergent aspects of the influence of sexual selection and group cohesion in the evolution of human musicality, integrating it with the other arts. This thesis consists of four studies covering natural experiments and real controlled ones, using direct and self-report assessments of both the 15 musical appreciation and production. We used methods that require the collaboration of the participants (questionnaires and recordings of the singing), and methods using discrete measurements (such as official statistics of vestibular since 1980). And we sampled a wide variety of undergraduate and graduate courses in different regions of Brazil (Sao Paulo and Natal) and abroad (the Netherlands and Canada). The overall results revealed cross-culturally and temporally the existence of sex differences, more on the motivational side to music and other arts than on specific skills. Men are more focused on instrumental music production, while women are more devoted to singing, dance, music appreciation and all other art forms. Sexual strategies were related to displays such as singing and playing for men, and the importance of music and music appreciation for women. Imagining oneself in a context of group cohesion influenced the person perception of the musicians by their music for men, and romantic context influenced womens judgment about the musicians. Both sexual selection and group cohesion proved to be interrelated in new ways. A broad and inclusive way of viewing the evolution of human musicality and other arts has emerged from the confluences of results as their implications

O comportamento animal associado a características morfológicas fornece evidências para um melhor entendimento de como o comportamento sexual tem evoluído, e como os organismos podem maximizar seu sucesso reprodutivo. Fatores como tamanho, reservas de energia e outros caracteres sexuais como a coloração são essenciais para o melhor desempenho em relação a outros indivíduos da mesma espécie. Estes podem transmitir informação da qualidade do macho para outros machos co-específicos como também para às fêmeas. Esta qualidade, guarda relação com a condição física (reservas de energia) que possuem, e é necessária para ter sucesso na reprodução. Sendo a reprodução uma das mais custosas em términos energéticos em comparação a outras atividades, é de se esperar que os animais invistam a maioria das reservas no comportamento reprodutivo, o qual influencia no tipo de estratégia que eles adotam e à duração em tempo das interações relacionadas a reprodução, entre outras. Portanto indivíduos com características melhor desenvolvidas ou com boa condição física, terão uma vantagem na reprodução que os outros indivíduos da comunidade. Zenithoptera lanei é uma espécie neotropical presente no Brasil, da qual se tem poucos estudos sobre sua ecologia comportamental, sendo uns dos mais importante o realizado por Guillermo-Ferreira no 2015, para descrever as estruturas que conformam esta pruinosidade e sua função na comunicação intraespecífica. Neste estudo, descrevemos o comportamento sexual de Z. lanei (Libellulidae), com a hipótese que nesta espécie apresentam machos territoriais, e que a coloração de suas asas, o tamanho corporal e a reserva de energia (gordura) devem desempenham um papel importante na condição territorial. Assim, os machos com maior quantidade de energia e maior tamanho deveriam ganhar disputas, defender territórios e, portanto, manter a condição territorial. Além, avaliamos também se essa condição de territorialidade poderia influenciar o tempo de duração das cópulas e a oviposição pelas fêmeas. Os resultados mostraram que machos são territoriais, e esta territorialidade está relacionada com a condição física e tamanho. Sendo que, machos com maior tamanho corporal e maior quantidade de reservas de energia ganharam mais disputas e mantiveram um território. Apesar dos machos serem territoriais, não houve diferença entre a duração do tempo das interações reprodutivas para machos vencedores em comparação aos machos perdedores, indicando que o tempo de duração das interações reprodutivas não são influenciadas pela condição de territorialidade do macho. / Animal behavior associated with morphological characteristics supplies evidence for a better understanding of how sexual behavior has evolved, and how organisms can maximize their reproductive success. Factors such as size, fat reserves and other sexual characters such as coloration are essential to individual better performance in relation to conspecifics. These factors? Can bring information of the male quality to other conspecifics and females. This quality keeps relation with the physical condition (energy reserves) that they have which is required to succeed in breeding, as reproduction is one of the most expensive activity in energy cost in relation to other activities. The reproductive behavior is related to the individual fat reserves that influences, among other factors, in the condition that they adopt and to the duration in time of the related interactions to reproduction. Therefore, individuals with more developed characteristics or with better physical conditions will have an advantage in the reproduction comparing with other individuals of the community. The dragonfly Zenithoptera lanei is a Neotropical species present in Brazil, only studied so far by Guillermo-Ferreira in 2015, when structures that conform this pruinosity and his function in the intraspecific communication were described. In this study, describe the sexual behavior of Z. lanei (Libellulidae). Was hypothesized that in this species males present territorial behavior, and that the coloration of wings, body size and the energy reserves (fat) may play an important role in territorial condition and reproductive success. Thus, males with higher quantity of energy and larger size should win more disputes, defend territories and, therefore, maintain the territorial condition. In addition, was also assessed whether this condition of territoriality may influence the duration of the copulation and oviposition by females. The results showed that males are territorial, and its territoriality keeps relation with size and the physical condition. In other words, males with larger body and higher energy reserves have won more disputes and maintained a territory. Although males were territorial, there was no difference between the duration of reproductive interactions, winning males and losers, thus indicating that the reproductive interactions are not influenced by the condition of territoriality of the male.

A musicalidade, concebida como o conjunto da capacidade cognitiva subjacente à dança e à comunicação sonora por meio de melodias harmonizadas e ritmadas, satisfaz vários critérios que caracterizam as adaptações biológicas. A música é muito antiga, universal e um importante aspecto em todas as culturas e épocas conhecidas. Ela provoca emoções e reações estéticas fortes, se desenvolve segundo um roteiro ontogenético padrão, envolve uma capacidade neurocognitiva especializada em receber, processar e produzir música, traz benefícios à saúde e apresenta fatores hereditários nas diferenças individuais, consome muita energia e tempo, e tem análogos na sinalização acústica de outras espécies sugerindo homologia e convergência adaptativa. Existem duas principais teorias acerca do valor adaptativo para a musicalidade: coesão grupal e seleção sexual. Elas não são excludentes ou incompatíveis e apresentam muitas sobreposições. Ambas buscam, em diferentes contextos sociais, as pressões seletivas envolvidas na valorização ancestral dos responsáveis pela produção musical e sua apreciação. Entretanto, elas diferem quanto ao grau de diferenças sexuais previsto: a coesão de grupo prevê poucas diferenças sexuais, mas para a seleção sexual as mulheres seriam mais voltadas para apreciação musical, enquanto os homens seriam mais voltados para a exibição musical via instrumento musical. O maior desafio para o enfoque adaptacionista da musicalidade é a ampliação do teste experimental de hipóteses. O objetivo geral desta tese é investigar empiricamente, por meio de diferentes propostas metodológicas, aspectos divergentes e convergentes das influências da seleção sexual e da coesão de grupo na evolução da musicalidade humana integrada às outras artes. Esta tese consiste de quatro estudos que abrangem experimentos naturais e verdadeiros controlados, acessando de forma direta e 13 através de auto-relato tanto a apreciação quanto a produção musical, usando metodologias que requerem a colaboração dos participantes (questionários e gravações do canto), e outras com medidas discretas (como estatísticas oficiais de vestibulares desde 1980), amostrando ampla variedade de cursos de graduação e pós em diferentes regiões do Brasil (São Paulo e Natal) e no exterior (Holanda e Canadá). O conjunto dos resultados revela interculturalmente e temporalmente a existência de diferenças sexuais mais quanto às motivações e disposições para e musicalidade e outras artes do que para capacidades específicas. Os homens são mais voltados para a produção musical instrumental, enquanto as mulheres são mais voltadas para a produção musical cantada, dança, apreciação musical e outras manifestações artísticas. As estratégias sexuais se relacionaram à exibição musical cantada e tocada para os homens, e à importância e apreciação musical para as mulheres. Imaginar-se em um contexto de coesão grupal influencia mais o julgamento dos músicos a partir da música para os homens e num contexto amoroso mais para as mulheres. Ambas, seleção sexual e a coesão de grupo se mostraram inter-relacionadas de novas maneiras. Uma visão ampla e integradora sobre a evolução da musicalidade e das outras artes emergiu do conjunto de resultados e suas implicações / The human musicality, considered as a set of underlying cognitive abilities to dance and sound communication through harmonized rhythmic melodies, meets several criteria which characterize biological adaptations. Music is very old, and an important aspect in all cultures and known past historical periods. It provokes strong emotions and aesthetic responses, it unfolds according to a standard developmental schedule, involves a specialized neurocognitive ability in its perception, processing and production, it gives health and psychological benefits, and there is some hereditary factors on individual differences. It is also very energy-intensive and time consuming, and there are some similarities to the acoustic signalling of other species, suggesting homology and adaptive convergence. There are two main theories about the adaptive values for human musicality, group cohesion and sexual selection. They are not mutually exclusive or incompatible, and exhibit much overlap. Both seek, in different social contexts, the selective pressures involved in the ancestral advantages for music production and appreciation. However, they differ in predictions related to sexual differences: the group cohesion predicts few sex differences, whereas sexual selection predicts that women would be more dedicated to music appreciation, while men would be more focused on displaying via musical instrument. The biggest challenge to the adaptationist approach to musicality is the expansion of the empirical testing of hypotheses. The aim of this thesis is to empirically investigate, using different methodological approaches, divergent and convergent aspects of the influence of sexual selection and group cohesion in the evolution of human musicality, integrating it with the other arts. This thesis consists of four studies covering natural experiments and real controlled ones, using direct and self-report assessments of both the 15 musical appreciation and production. We used methods that require the collaboration of the participants (questionnaires and recordings of the singing), and methods using discrete measurements (such as official statistics of vestibular since 1980). And we sampled a wide variety of undergraduate and graduate courses in different regions of Brazil (Sao Paulo and Natal) and abroad (the Netherlands and Canada). The overall results revealed cross-culturally and temporally the existence of sex differences, more on the motivational side to music and other arts than on specific skills. Men are more focused on instrumental music production, while women are more devoted to singing, dance, music appreciation and all other art forms. Sexual strategies were related to displays such as singing and playing for men, and the importance of music and music appreciation for women. Imagining oneself in a context of group cohesion influenced the person perception of the musicians by their music for men, and romantic context influenced womens judgment about the musicians. Both sexual selection and group cohesion proved to be interrelated in new ways. A broad and inclusive way of viewing the evolution of human musicality and other arts has emerged from the confluences of results as their implications

Inbreeding can have profound negative effects on individuals by reducing fertility and viability. In populations, inbreeding depression can reduce growth rates and increases extinction risk. The aims of this thesis are to investigate inbreeding depression in male guppies (Poecilia reticulata) and to study the evolution of mechanisms for inbreeding avoidance in females, using guppies from a feral population in Queensland, Australia. Male guppies are highly polymorphic in their sexual ornamentation, indeed they show one of the most extreme polymorphisms observed in nature. Female guppies exhibit complex mate choice based on preferences for ornamentation, as well as social context. I aim is to examine how these factors of inbreeding avoidance alter sexual selection. In male guppies I found strong inbreeding depression in male sperm numbers, which is amplified under semi-natural compared to laboratory conditions (Chapter 2). Moreover, inbreeding depression results in low fertility under sperm competition: an experiment using artificial insemination techniques reveals that highly inbred males are heavily disadvantaged in gaining paternity (Chapter 3). On population level, inbreeding depression is manifest in reduced growth rates, predominantly in the early stages of inbreeding (Chapter 4). Population growth at inbreeding coefficients f=0.375-0.59 did not seem to lead to inbreeding depression, whereas lower levels of inbreeding reduced population growth. Although the growth rates in inbred populations appear normal, severe inbreeding depression is uncovered after outbred immigrants are added. Specifically, male immigrants are most efficient in short-term genetic rescue, probably due to insemination of large numbers of females whereas females are limited in the number of eggs they can produce (Chapter 4). Male ornamental traits show significant inbreeding depression in semi-natural conditions only (Chapters 2 & 3). Inbreeding avoidance mechanisms seem to have evolved in females: they prefer courtship displays of non-inbred males (Chapter 2), unfamiliar males (Chapter 5) and males with rare patterns (Chapter 6). This preference might increase the mating success of immigrants, and may have evolved to facilitate the avoidance of inbreeding. Together with context-independent preferences for ornament combinations (Chapter 6), it also offers an explanation for the maintenance of polymorphism in this species.

Inbreeding can have profound negative effects on individuals by reducing fertility and viability. In populations, inbreeding depression can reduce growth rates and increases extinction risk. The aims of this thesis are to investigate inbreeding depression in male guppies (Poecilia reticulata) and to study the evolution of mechanisms for inbreeding avoidance in females, using guppies from a feral population in Queensland, Australia. Male guppies are highly polymorphic in their sexual ornamentation, indeed they show one of the most extreme polymorphisms observed in nature. Female guppies exhibit complex mate choice based on preferences for ornamentation, as well as social context. I aim is to examine how these factors of inbreeding avoidance alter sexual selection. In male guppies I found strong inbreeding depression in male sperm numbers, which is amplified under semi-natural compared to laboratory conditions (Chapter 2). Moreover, inbreeding depression results in low fertility under sperm competition: an experiment using artificial insemination techniques reveals that highly inbred males are heavily disadvantaged in gaining paternity (Chapter 3). On population level, inbreeding depression is manifest in reduced growth rates, predominantly in the early stages of inbreeding (Chapter 4). Population growth at inbreeding coefficients f=0.375-0.59 did not seem to lead to inbreeding depression, whereas lower levels of inbreeding reduced population growth. Although the growth rates in inbred populations appear normal, severe inbreeding depression is uncovered after outbred immigrants are added. Specifically, male immigrants are most efficient in short-term genetic rescue, probably due to insemination of large numbers of females whereas females are limited in the number of eggs they can produce (Chapter 4). Male ornamental traits show significant inbreeding depression in semi-natural conditions only (Chapters 2 & 3). Inbreeding avoidance mechanisms seem to have evolved in females: they prefer courtship displays of non-inbred males (Chapter 2), unfamiliar males (Chapter 5) and males with rare patterns (Chapter 6). This preference might increase the mating success of immigrants, and may have evolved to facilitate the avoidance of inbreeding. Together with context-independent preferences for ornament combinations (Chapter 6), it also offers an explanation for the maintenance of polymorphism in this species.

<p>The evolutionary goal of individuals is reproduction and sexual selection favours traits improving reproductive success. When males invest less than females in offspring, males have potentially a higher reproductive rate than females. This typically results in sex-specific reproductive strategies of male-male competition and female choice of mating partner. Under polyandry, sexual selection can continue after copulation as sperm competition and cryptic female choice. This thesis focuses on male and female pre- and post-copulatory reproductive strategies in the promiscuous red junglefowl, <i>Gallus</i> <i>gallus ssp.</i>, and its domestic subspecies the domestic fowl, <i>Gallus gallus</i> <i>domesticus</i>. Males impose high re-mating rates on females, which triggers female resistance in copulations. In addition, when sexual harassment increases, females re-mate at times of day when male mating propensity is lower, to avoid intense sexual harassment. Males allocate sperm supplies differentially according to (i) variation in female polyandry and own competitive ability, (ii) earlier sperm investment in a female, and (iii) female reproductive quality, signalled by female comb size. Males also perform ‘aspermic’ copulations (i.e. copulations with no semen transfer), which inhibit polyandry and in turn reduce sperm competition. In mating opportunities with relatives, males do not avoid inbreeding. However, females avoid inbreeding before copulation through kin recognition and after copulation by selecting against related males’ sperm. These results show that selection on males to re-mate at higher rates than females and copulate indiscriminately according to partner relatedness, trigger counteracting female responses, creating the potential for sexual conflict over fertilisation. Teasing apart pre- and post-copulatory strategies and the contribution of each sex therefore becomes crucial in order to understand the evolution of reproductive strategies and the mechanisms affecting paternity.</p>

<p>Female reproductive decisions have been suggested to be highly influenced by mate quality. I have studied whether offspring quality may be adjusted by females to match the attractiveness of males and how strong control females have over their reproductive investment focusing on egg size. This was done in the Banggai cardinalfish (Pterapogon kauderni), a sex-role reversed obligate paternal mouthbrooder where males invest heavily into reproduction. As this species is suitable for both laboratory experiments and field studies it is an ideal candidate for the study of reproductive investment. </p><p>Mating was size-assortative and both males and females benefited from pairing with large partners. However, male size determined the reproductive output of a pair. Females courted large males more intensively and produced larger, but not fewer eggs when mated to large males as compared to small males. Further, this matching of egg size to mate attractiveness may be fast. Female courtship behaviours contained honest information regarding both clutch weight and egg maturity, traits that may be highly important for male mate choice. Surprisingly, males played an important part in territory defence suggesting relatively equal sex-roles in this species. Also, this species showed stable group structures which may be important for the evolution of female plasticity in reproductive investment due to high variance in quality of available mates. </p><p>This thesis suggest that females have a remarkable control over their reproductive investments and that male quality may be highly influential on reproductive decisions regarding offspring quality. Furthermore, it suggest that sexual selection may have strong effects on the evolution of egg size and parental care on a whole.</p>

<p>In this thesis, different genetic tools are used to investigate pre- and postzygotic barriers to gene exchange and their role in speciation in the pied flycatcher (<i>Ficedula hypoleuca</i>) and the collared flycatcher (<i>F. albicollis</i>). This species complex consists of four genetically distinct clades that apparently diverged in allopatry (I). Sequencing of introns from autosomal and Z-linked genes from the two species reveals signs of selection on the Z-chromosome. Sexual selection acting on Z-linked genes might explain this pattern (II). By using large-scale genotyping of single nucleotide polymorphisms (SNPs), introgression is observed at autosomal- but not Z-linked loci, mostly from the pied- to the collared flycatcher. Male plumage characters and genes involved in hybrid fitness are largely mapped to the Z-chromosome (III). By studying mate choice of female hybrids I show that there is a link between female preferences and the Z chromosome (IV). The rate of introgression in island versus clinal hybrid zones is consistent with regional differences in hybrid fertility. Asymmetric gene flow from allopatry on the islands may oppose reinforcement, leading to introgression and a partial breakdown of postzygotic isolation. Adaptive introgression may explain the high rate of introgression observed at one of the genetic markers (V). For late breeding female collared flycatchers it appears to be adaptive to use pied flycatchers as social fathers but conspecific males as genetic fathers. Additionally, females in mixed species pairs may reduce hybridization costs by producing an excess of male hybrid offspring that are more fertile than females (VI).</p><p>In conclusion, the Z-chromosome appears to play a major role in flycatcher speciation. Sexual selection and reinforcement are important mechanisms in the divergence of these birds. However, gene flow from allopatry, introgression of adaptive genes and adaptive hetrospecific pairing by late breeding collared flycatcher females may work in the opposite direction.</p>