Cooperation And Competition In Kin Associations

Abstract

The presence of nearby kin, kin-directed cooperation across territory boundaries, and kin competition over extra-pair matings are potentially important influences on social evolution, yet our understanding of the complex relationships among these factors is incomplete. For example, the costs of kin competition can theoretically select for dispersal, yet other theory suggests that kin-selected reductions in the intensity of competition may counteract these costs and allow individuals to reap other benefits of kin-based living. Using both theoretical and empirical approaches, I investigate how kin structure and extra-pair mating affect each other as well as cooperative behavior. In the first chapter, I investigate competition between unrelated males over extra-pair paternity, deriving the conditions under which females are selected to invest in conflict and suggesting that males may maximize their fitness by associating in "hidden leks." In the second chapter, I show how genetic mating system and kin structure can affect the relative costs and benefits of helping versus independent breeding, suggesting that kin structure may in fact increase the benefits of breeding independently relative to rearing younger siblings. In the third chapter, I examine the effects of relatedness on extra-pair mating competition, and the effects of this kin competition on the costs and benefits of philopatry. I demonstrate that the reduced optimal investments in competition among kin mean that males benefit from philopatry, even in the face of paternity loss, and that paternity gains are skewed towards the relative with higher heritable genetic quality. In the fourth chapter, I experimentally investigate the cryptic cooperative behaviors that are expressed in western bluebird (Sialia mexicana) kin neighborhoods. I find that, while first-order male relatives exhibit cross-territorial assistance responses in dire situations, these responses are less frequent than those by stay-at-home helpers. In the fifth chapter, I examine the effects of kin presence on western bluebird extra-pair mating, and suggest that patterns resulting from kin-based living, such as paternity buffering, may influence the population genetic mating system. Together, these results indicate that the complex, and often cryptic, cooperative and competitive interactions that occur among independently breeding relatives in kin neighborhoods can importantly affect social evolution.