Understanding the evolution of infidelity using the Seychelles warbler system

Across socially monogamous species – where individuals form pairs to breed – infidelity is a common occurrence. However, the forces underlying its evolution are still unclear. In this thesis, I investigated several potential drivers of infidelity in the Seychelles warbler. This is a socially monogamous species with high rates of infidelity and individuals living in either pairs or groups (consisting of a breeding pair and subordinates that can help rear offspring). Moreover, I addressed a consequence of infidelity in the Seychelles warbler, i.e. the contribution of extra-group paternity (EGP) to the variance in male reproductive success. I showed that a social condition – group size – was positively associated to female infidelity. Moreover, patterns of male and female extra-group reproduction were age-dependent (changing within-individuals with age). In males, such age-related changes probably altered the age-specific contribution of EGP to the variance in reproductive success. Upon addressing whether infidelity enabled females to gain indirect genetic benefits – i.e. to increase the genetic quality of their offspring – I provided limited evidence that females use extra-group reproduction to avoid inbreeding (indirect non-additive genetic benefits). Further, I found that the age-related patterns of infidelity did not offer evidence that females use extra-group reproduction to acquire high-quality paternal alleles in offspring (indirect additive genetic benefits). Moreover, I showed that heritability of female extra-group reproduction was moderately low. These findings suggest that infidelity is unlikely to evolve via indirect additive genetic benefits in the Seychelles warbler. Other mechanisms may be at play in the evolution of this enigmatic mating strategy.