Evolution in Darwin's Dream Ponds: The Cichlid Fishes of the East African Big Lakes

More than one and a half centuries after the publication of Charles R. Darwin’s The Origin of Species, the identification of the processes governing the emergence of novel species remains a fundamental question to biology. Why is it that some groups have diversified in a seemingly explosive manner, while other lineages have remained unvaried over millions of years? What are the external factors and environmental conditions that promote diversification? And what is the molecular basis of adaptation, evolutionary innovation and diversification? A key to these and related questions is the comparative study of exceptionally diverse yet relatively young species assemblages that have radiated in geographically well-defined areas, such as the Darwin’s finches on the Galapagos archipelago, the Caribbean Anoles lizards or the cichlid fishes in the Great Lakes of East Africa. Lakes Tanganyika, Malawi, and Victoria are each teeming with a unique set of hundreds of endemic cichlid species, which have evolved in the last few millions to several thousands of years only. East Africa’s cichlid species differ greatly in ecologically relevant, hence naturally selected, characters such as mouth morphology and body shape, but also in sexually selected traits such as coloration. One of the most fascinating aspects of cichlid evolution is the frequent occurrence of evolutionary parallelisms between and even within lakes as consequence of the independent adaptation to the same ecological niches.