Microevolutionary Processes and Macroevolutionary Patterns of Diversification in Cichlid Fishes: Lessons from Extremely Young Species Flocks

摘要

The exceptionally diverse species flocks of cichlid fishes in the East African Great Lakes are promi-nent examples for replicate adaptive radiations and explosive speciation. The hundreds of closely related cichlid species often differ greatly in ecologically relevant traits such as mouth morphology and dentition. These patterns of convergent evolution across lakes will be discussed in light of the patterns of ecological diversification of these species flocks. Cichlids also display a great diversity in coloration and pigmentation patterns indicating the importance of sexual selection in this group. We have studied the molecular evolution of several candidate color genes in East African cichlid species and find evidence for adaptive sequence evolution in some of them. For example, we can show that / csfl ra/ evolved under positive selection in the ancestor of the haplochromines (the most species-rich group of cichlids), in which this gene is expressed in the egg-dummies on male anal fins. These egg-spots mimic real eggs and play a crucial role in the breeding cycle of these mouth-brooding fish by guiding the female's mouth close to the male's genital opening. This facilitates the fertilization of the eggs within the female's mouth. The comparative analysis of color genes also provides novel insights into the general patterns of evolution in East African cichlids. The mechanisms of speciation were studied in Nicaraguan crater lakes in detail. In these ecological settings species were found to have arisen in record speed and often through sympatric speciation.