Better together: Cooperative breeding under environmental heterogeneity

Cooperative breeding – where more than two individuals engage in rearing offspring – has historically been attributed to a lack of independent breeding opportunities and high levels of within-group relatedness. However, cooperation often occurs between non-relatives and in non-saturated environments, suggesting alternative evolutionary causes of cooperative breeding. Environmental conditions can strongly influence the evolution of cooperative breeding, for instance when low food availability or high predation risk affects the costs of dispersal, or when cooperation under such conditions is necessary to successfully raise young. In this thesis, I investigate the relationship between environmental conditions and important components of cooperative breeding, using two distinct systems: the Seychelles warbler Acrocephalus sechellensis and the social cichlid Neolamprologus pulcher. This study offers three main conclusions. First, I argue that predation risk, while acknowledged as an important factor promoting group-living, is also an important driver of cooperative breeding and social complexity. Second, cooperative breeding has been suggested to function as a bet-hedging strategy, where groups allow reproduction under adverse conditions such as low food abundance. I show that this conclusion might be premature and that periods of low food abundance may lead to group formation, but not to cooperative breeding per se. Third, while subordinates in cooperative breeders have been suggested to make the best of a bad job, I argue that these conclusions may change if the ecological and environmental conditions under which breeding occurs are considered. Together, this thesis shows the importance of the environment and ecology for the evolution of cooperative breeding in vertebrates.