Dissertation

Adaptive responses to environmental changes in Lake Victoria cichlids

Promotor: Prof.dr. M.K. Richardson, Co-Promotor: F. Witte

Author: J.C. van Rijssel
Date: 05 March 2014
Links: Thesis in Leiden Repository

Lake Victoria cichlids show the fastest vertebrate adaptive radiation known which is why they function as a model organism to study evolution. In the past 40 years, Lake Victoria experienced severe environmental changes including the boom of the introduced, predatory Nile perch and eutrophication. Both environmental changes resulted in a decline of haplochromine cichlid species and numbers during the 1980s. However, during the 1990s and 2000s, some haplochromine species recovered. With the use of the unique Lake Victoria cichlid of collection of the Naturalis Biodiversity Center, this thesis showed how the haplochromines have adapted their ecomorphology to the changed environment. In response to a decrease in water clarity, increased predation, larger prey and low dissolved oxygen levels, these fish adapted their eyes, body shape, upper jaw and gills in a way that would be beneficial to the survival of the fish. These adaptive responses could be the result of phenotypic plasticity or genetically based changes such as natural selection or hybridization or a combination of these three mechanisms. This research showed that the Lake Victoria cichlids are able to adapt extremely fast which is likely to have contributed to their extreme fast adaptive radiation.