Nile perch was introduced in Lake Victoria in the 1950s and exploded in number during the 1980s. The process of colonization of the lake by this predatory fish is described and explained. The... Show moreNile perch was introduced in Lake Victoria in the 1950s and exploded in number during the 1980s. The process of colonization of the lake by this predatory fish is described and explained. The changes in a number of other fauna elements of Lake Victoria are described and explained. Not only Nile perch is to blame for these changes. Human influence by introducing other fish species, fisheries and agricultural practices have their impact Show less
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... Show moreThe 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. Show less
