| Summary: | <p>In cooperatively breeding species, groups of three or more individuals cooperate in raising young. The challenge is to explain why investing in another individual’s reproduction is a better strategy for transmitting genes to future generations than breeding independently. Theoretically, individuals cooperate either because it increases their own reproduction (direct fitness) or because it increases the reproductive success of relatives with whom they share genes (indirect fitness). Life history and demographic parameters are expected to influence the direct and indirect fitness benefits of cooperating. However, how these parameters shape the evolution of cooperative breeding remains largely unexplored. In this thesis, I develop our understanding of the role of life history and demographic parameters in the evolution of cooperative breeding using birds as a model system. Specifically: 1) I review the role of longevity in the evolution of cooperative breeding; 2) I demonstrate that long life makes the evolution of cooperative breeding more likely, supporting a theoretical prediction that territory inheritance is an important incentive for helping behaviour; 3) I show that female helpers invest more in raising siblings than male helpers when they have a higher probability of breeding in their natal group, which suggests that future breeding opportunities shape investment in helping as relatedness of male and female helpers to their siblings is equal; 4) I show that ancestral polyandry only influences the likelihood of cooperative breeding evolving in family groups, not in non-family groups, and that there is a reproductive division of labour in family groups while nonfamily groups are smaller and consist of co-breeders; 5) Finally, I test whether breeders adjust their investment in parental behaviour when they have helpers at the nest in response to the reproductive costs of care.</p>
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