Social factors affecting female behavior, ecology, and fitness in wild bottlenose dolphins
Wallen, Megan Marie
In humans and non-human animals alike, the social environment presents context-dependent costs and benefits. Some species face extreme pressures resulting from divergent fitness traits among the sexes, leading to pronounced sexual conflict. In this dissertation, I capitalize on the 30-year longitudinal dataset on Shark Bay bottlenose dolphins (Tursiops aduncus) to understand how the fission-fusion society facilitates preferred associations and emergence of social network properties that influence fitness. Specifically, I investigate how the coercive mating system influences intersexual associations and imposes ecological costs from a perspective not often taken – that of the adult female. Social dynamics impact female reproduction, and may serve to mitigate consequences of male harassment.Chapter 1 characterizes patterns of intersexual association near conception. Females increase association with adult males just prior to conception, but juvenile male association always remains low. As expected, intersexual associations dropped off significantly post-conception, demonstrating males could detect pregnancy fairly early. Surprisingly, despite a system of bisexual philopatry whereby males and females remain in their natal area for life, mothers and weaned sons did not appear to exhibit avoidance patterns, except during the mothers’ fertile periods.Chapter 2 quantifies the ecological costs to females when in the presence of adult males, who present a threat of sexual coercion. Females appear to suffer an ecological cost to increased male association, in that preferred ranging and habitat use patterns are constrained. However, the interaction between male impact and female reproductive status demonstrates that cycling females experience the greatest impact.Finally, Chapter 3 explores the early differentiation of social tactics in juvenile female dolphins, and quantifies the relationship between social network measures and fitness. Several metrics predict calving success, but surprisingly network centrality is not a strong influence. These results suggest that strong, differentiated dyadic bonds, likely with kin, are beneficial during development and aid in later reproductive success.This work contributes to our understanding of how animals, females in particular, exploit and mitigate the unique social pressures of a coercive mating system, and highlights the importance for future studies to quantify the fitness benefits and consequences of social relationships in a free-ranging, socially complex mammal.
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