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Classical theories of how animals make mate choices have focused on each sex's inherited preferences for the other sex's traits or behaviours. The present thesis was undertaken to investigate how social factors play a role in determining an animal's choice of mate. In the series of experiments reported here, 'focal' female and male Japanese quail were given the opportunity to observe another quail (a 'model') of the same sex mating with a conspecific of the opposite sex (a 'target'). Results of experiments described in chapters 2 and 3 revealed that focal females: (1) displayed an increased tendency to affiliate with male targets that they had observed mating with model females, and (2) found a target male more attractive if he had been observed just standing near another female. In Chapter 4, social influences or male mate choice were investigated. Focal males: (1) exhibited a decrease in their preference for female targets that they had observed mating with model males, and (2) showed a decrease in preference for a female target only if she had been seen mating with or being courted by a model male, not simply standing near him. Finally, in chapter 5, it was determined that for quail of both sexes, affiliation time was a reliable predictor of focal subjects' actual choice of a mate. Taken together, these results are consistent with the hypothesis that females gain benefits from attending to the mate choices of other females, whereas for males there is a cost associated with mating with a female that had recently muted with another male. / Thesis / Doctor of Philosophy (PhD)

<p>Harmony and cooperation was for long believed to dominate sexual interactions. This view slowly started to change 25 years ago and is today replaced with a view where males and females act based on what is best from a costs-benefits perspective. When sex specific costs and benefits differ, concerning reproductive decision influenced by both sexes, sexual conflict will occur. The basis for discordant reproductive interests between the sexes is that males produce many small gametes, while females’ produce few and large gametes. One result of this difference is that the optimal mating rate differs between the sexes. Males, with their many small sperm, maximize their reproductive output by mating with many females, while females often do best by not mating more frequently than to fertilize their eggs, since mating often entails a cost. Sexual conflict over mating is thus an important factor shaping the interactions between the sexes. In this thesis I study this and related conflicts between the sexes, using mathematical models, fruit flies and comparative methods. Mathematical modelling was used to explore how males and females may coevolve under sexual conflict over mating. This model shows that sexual conflict over mating results in the evolution of costly female mate choice, in terms high resistance to matings, and costly exaggerated male sexual traits, aimed to manipulate females into mating. A key assumption in this model is that males which females find attractive also are more harmful to females. This assumption was tested by housing fruit fly females with either attractive or unattractive males. Females kept with attractive males were courted and mated more, and suffered a 16 percent reduction in lifetime offspring production. In another study I measured genetic variation in two antagonistic male traits used to compete over females; offence - a male’s ability to acquire new mates and supplant stored sperm, and defence - a male’s ability to induce fidelity in his mates and prevent sperm displacement when remating occurs. Independent additive genetic variation and positive selection gradients were found for both these traits, indicating an ongoing arms race between these male antagonistic traits. This arms race also had a negative impact on females, since high values of offence compromised female fitness. Genetic variation in female ability to withstand male harm was also tested for and found, indicating that females evolve counter adaptations to reduce the effect of harmful male traits. Finally, the proposed link between sexual conflict and speciation was tested. Theory suggests that perpetual sexual arms races will cause allopatric populations to evolve along different evolutionary trajectories, resulting in speciation. This theory was tested using comparative methods by contrasting the number of extant species in taxa with high and low opportunity for sexual conflict. The study showed that taxa with high opportunity for sexual conflict, on average, has four times as many species as those with low opportunity, supporting that sexual conflict is a key process in speciation.</p>

Harmony and cooperation was for long believed to dominate sexual interactions. This view slowly started to change 25 years ago and is today replaced with a view where males and females act based on what is best from a costs-benefits perspective. When sex specific costs and benefits differ, concerning reproductive decision influenced by both sexes, sexual conflict will occur. The basis for discordant reproductive interests between the sexes is that males produce many small gametes, while females’ produce few and large gametes. One result of this difference is that the optimal mating rate differs between the sexes. Males, with their many small sperm, maximize their reproductive output by mating with many females, while females often do best by not mating more frequently than to fertilize their eggs, since mating often entails a cost. Sexual conflict over mating is thus an important factor shaping the interactions between the sexes. In this thesis I study this and related conflicts between the sexes, using mathematical models, fruit flies and comparative methods. Mathematical modelling was used to explore how males and females may coevolve under sexual conflict over mating. This model shows that sexual conflict over mating results in the evolution of costly female mate choice, in terms high resistance to matings, and costly exaggerated male sexual traits, aimed to manipulate females into mating. A key assumption in this model is that males which females find attractive also are more harmful to females. This assumption was tested by housing fruit fly females with either attractive or unattractive males. Females kept with attractive males were courted and mated more, and suffered a 16 percent reduction in lifetime offspring production. In another study I measured genetic variation in two antagonistic male traits used to compete over females; offence - a male’s ability to acquire new mates and supplant stored sperm, and defence - a male’s ability to induce fidelity in his mates and prevent sperm displacement when remating occurs. Independent additive genetic variation and positive selection gradients were found for both these traits, indicating an ongoing arms race between these male antagonistic traits. This arms race also had a negative impact on females, since high values of offence compromised female fitness. Genetic variation in female ability to withstand male harm was also tested for and found, indicating that females evolve counter adaptations to reduce the effect of harmful male traits. Finally, the proposed link between sexual conflict and speciation was tested. Theory suggests that perpetual sexual arms races will cause allopatric populations to evolve along different evolutionary trajectories, resulting in speciation. This theory was tested using comparative methods by contrasting the number of extant species in taxa with high and low opportunity for sexual conflict. The study showed that taxa with high opportunity for sexual conflict, on average, has four times as many species as those with low opportunity, supporting that sexual conflict is a key process in speciation.

The evolution of elaborate male ornaments via sexual selection is well-understood while the selective pressures acting on female ornaments remains unresolved. Female ornaments in species with strong sexual selection on the male homologue of the ornament were originally thought to result from an intersexual genetic correlation. My thesis explores the evolution of ornaments in females due to direct selection by developing theoretical models and examining the biology of a neotropical mosquito (Sabethes cyaneus) with sexually homologous ornaments coinciding with male-male competition. I began by exploring the morphology of the ornaments in both sexes of S. cyaneus. Sexual dimorphism in the size and shape of the ornaments was slight and both male and female ornaments showed classic hallmarks of sexually selected traits. I then tested for direct selection on S. cyaneus male and female ornaments via mutual mate choice. I found evidence of male, but surprisingly not female, preferences for ornaments. I then further considered the evolution of male mate choice in polygynous species. First, I investigated whether male investment in courtship by S. cyaneus may result in a lower operational sex ratio and thereby reduce the costs associated with male mate choice. Male courtship did pose a significant longevity cost to male S. cyaneus. Second, I explored the possibility that a female preference for male courtship effort may contribute to the benefits of male mate choice in a series of population genetic models. The spread of a male preference gene can be driven by female preferences for male courtship when males court preferred females more. Finally, I found that female S. cyaneus are not benefitting from signalling to increase their mating rate as they are monandrous. My thesis therefore challenges standing sexual selection theory and suggests that sexual selection on females may be more widespread than previously thought. / Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 729

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Music and language are both deeply rooted in our biology, but scientists have given far more attention to the neurological, biological and evolutionary roots of language than those of music. Because of this, and probably partially due to this, the purpose of music, in evolutionary terms, remains a mystery. Our brain, physiology and psychology make us capable of producing and listening to music since early infancy; therefore, our biology and behaviour are carrying some of the clues that need to be revealed to understand what music is “for”. Furthermore, music and language have a deep relationship, particularly in terms of cognitive processing, that can provide clues about the origins of music. Non-verbal behaviours, including voice characteristics during speech, are an important form of communication that enables individual recognition and assessment of the speaker’s physical characteristics (including sex, femininity/masculinity, body size, physical strength, and attractiveness). Vocal parameters, however, can be intentionally varied, for example altering the intensity (loudness), rhythm and pitch during speech. This is classically demonstrated in infant directed speech (IDS), in which adults alter vocal characteristics such as pitch, cadence and intonation contours when speaking to infants. In this thesis, I analyse vocal modulation and its perception in human social interaction, in different social contexts such as courtship and authority ranking relationships. Results show that specific vocal modulations, akin to those of IDS, and perhaps music, play a role in communicating courtship intent. Based on these results, as well the body of current knowledge, I then propose a model for the evolution of musicality, the human capacity to process musical information, in relation to human vocal communication. I suggest that musicality may not be limited to specifically musical contexts, and can have a role in other domains such as language, which would provide further support for a common origin of language and music. This model supports the hypothesis of a stage in human evolution in which individuals communicated using a music-like protolanguage, a hypothesis first suggested by Darwin.

Interest in the question of when and how species recognition and mate preferences emerge in animals with strong species-typical predispositions has faded since the time of the classical ethologists. In its place, the role of plasticity has surfaced as a central emphasis in the study of animal behavior. Here, I step back and examine the origin and execution of sexual behavior in a tropical frog for which auditory predispositions are key. These experiments challenge assumptions about behavioral development, auditory perception, and stereotyped behavior. First, I illustrate when and how a sex- and species-typical behavior—conspecific phonotaxis—emerges during development. This study demonstrates that phonotaxis, presumably restricted to mature females, is present in both sexes early in postmetamorphic development—potentially long before such behavior might serve an adaptive function. I place this result in the context of hypotheses regarding the development of learned versus non-learned behaviors, and in light of the potential for perception to be altered by physiological changes occurring concomitantly with ontogeny. Next, I describe a set of dynamic mate choice studies that highlight how decision-making in a relatively simple system is more flexible, and less stereotyped, than was previously assumed. Results here show that frogs temporally update their mate choice decisions in a moment-to-moment fashion as advertisement signals change in real time. By decomposing the decision-making process, I determine the stimulus parameters essential for commitment to an initial phonotactic approach. These studies are followed up by experiments that reveal a high level of individual variation in female choosiness during mate choice. Lastly, I describe a mate choice study that revealed categorical perception in frogs, the first “lower” vertebrate now known to exhibit a perceptual mode previously considered a hallmark of “higher” organisms. Collectively, I make the following arguments: (1) constraints on sensory systems play a larger role in shaping behavior than is generally appreciated, irrespective of the involvement of learning; (2) unstudied sources of variation may contribute significantly to the raw material for sexual selection; and (3) phonotaxis in anurans amphibians is not the simple, stereotyped behavior that has been suggested of it in the past. / text