Sexual selection and speciation: mechanisms in Lake Victoria cichlid fish

Abstract

The several hundred species of cichlid fish endemic to Lake Victoria (East-Africa) are textbook examples of explosive speciation. This thesis evaluates the hypothesis that sexual selection by female mate choice has contributed to this process of divergence, by investigating the mechanisms that drive the evolution and divergence of mating preferences for colour patterns. I studied two representative model systems, the highly polymorphic species Neochromis omnicaeruleus and the species pair Pundamilia nyererei and P. pundamilia. I used observational and experimental approaches in both laboratory and field. My work indicates that the interaction between sexual selection and habitat heterogeneity, in terms of photic environment and parasite exposure, can promote population divergence in male nuptial coloration and female preferences. In contrast, predation pressure and water turbidity may constrain the evolution and persistence of conspicuously coloured morphs and species.