The non-gradual nature of adaptive radiation in cichlid fishes of Lake Tanganyika

Adaptive radiation is the likely source of much of the ecological and morphological diversity of life on Earth. Owing to their spectacular taxonomic, phenotypic, ecological and behavioral diversity and propensity for explosive speciation, the assemblages of cichlid fishes in the African Great Lakes Victoria, Malawi and Tanganyika are prime role models for this evolutionary process. The cichlid fishes of Lake Tanganyika constitute the morphologically, ecologically and behaviorally most diverse cichlid species flocks. Our in-depth examination of nearly all its approximately 250 cichlid species revealed that this spectacular adaptive radiation proceeded in a non-gradual manner, in the form of three consecutive and trait-specific pulses of accelerated phenotypic evolution. Three trait complexes – body shape, mouth morphology, and the lower pharyngeal jaw bone – are highly diverse and show a particularly strong association with the environment. In addition, there is evidence that diversification with respect to behavior as well as pigment patterns contributed to the cichlid adaptive radiation in Lake Tanganyika.