Resumen de Vocal, behavioral, and genetic correlates of pair-living and serial monogamy in owl monkeys (aotus azarae) of Northeast Argentina
Understanding how a social organization and mating system can be beneficial, and hence, persist in populations, requires that we investigate the perspective of all individuals involved. However, in pair-living taxa, the role of solitary floaters, individuals that have dispersed from their groups and range unassociated with other reproductively mature individuals while seeking for a reproductive position in a social group, has been largely ignored when developing hypotheses and theoretical models. This has been so even when the existence of solitary floaters influences the Operational and Adult Sex Ratio of a population and increases the intrasexual competition with mated individuals. In pair living sexually monogamous taxa, despite the fact that the variance in reproductive success likely depends on the relative number of floaters-to-established pairs, the intrasexual competition has usually been assumed to be low. This dissertation explores the role that intrasexual competition between floaters and pairs has in the social organization and mating system of wild Azara´s owl monkeys (Aotus azare), a cathemeral, pair living and sexually monogamous South American primate. In the past, intrasexual competition has been associated with sexual dimorphism in several taxa. In chapter two, focusing on identified individuals of known sex and age, I evaluated the degree of sexual dimorphism in loud calls while evaluating the hypothesis of sex-biased vocal behavior. The reduced sexual dimorphism present in sexually monogamous species often hampers to properly evaluate morphological or behavioral traits that may have been influenced by sexual selection. However, in such taxa the formation of new pairs requires individuals to be able to identify, at least, the sex of the caller. This chapter presents evidence of sexual dimorphism in call structure, with females and males only emitting one type of call, each differing in dominant frequency and Shannon entropy. Further, the data support the hypothesis of sex-biased vocal behavior, with females emitting loud calls up to twice as much as males. Hence, I propose that Azara´s owl monkeys´ loud calls are sexually selected vocal traits that play a role in mate attraction. Likewise, my data suggest that this may be more important for females, likely because due to the extensive involvement of males in parental care in the species, females may face greater intrasexual competition in order to choose the best male. Based on this evidence of sexual dimorphism in loud calls, Chapter 3, explores the behavioral responses of mated pairs towards the simulated presence of male and female unfamiliar conspecific. As such, the main question of this chapter asks whether pairs primarily defend their territory or their mates. The data suggest that male and female owl monkeys guard their mates against competitors. Overall, males reacted more strongly than females and both sexes were more reactive to male than female unfamiliar calls, as evidenced by higher rates of sociosexual and vocal responses, movement towards the speaker, and intergroup encounters. Females guarding their partners against other males may be associated with their need to secure paternal investment. Likewise, the next chapter, four, narrow the focus on this hypothesis even further, and evaluates the relationship between the replacement of a biological father and the age of death of young individuals. My results strongly suggest that the presence of a new unrelated male is associated with lower infant survival in Azara´s owl monkeys, and that this association seems to be more important if the replacement occurs during the first year of life of individuals, when infants are still dependent on direct parental care. I propose that in owl monkeys care by the male is required and, in the absence of direct attacks towards infants, those can still die from neglect or insufficient paternal care. Finally, my dissertation ends with a detailed narrative of one male´s life that shows the different forms of intrasexual competition that Azara´s owl monkeys face through their life. Together, my study adds to our knowledge of intrasexual competition in pair-living sexual monogamous animals by documenting some of the ways in which social pressures influence the mating and parenting strategies of the species. Specifically, my study emphasizes the need of biparental care in the maintenance of the social organization and mating system of Aotus azarae
