Convergent Evolution within an Adaptive Radiation of Cichlid Fishes

The recurrent evolution of convergent forms is a widespread phenomenon in adaptive radiations (e.g., [1-9]). For example, similar ecotypes of anoles lizards have evolved on different islands of the Caribbean [2, 6], benthic-limnetic species pairs of stickleback fish emerged repeatedly in postglacial lakes [1, 3], equivalent sets of spider ecomorphs have arisen on Hawaiian islands [7, 8], and a whole set of convergent species pairs of cichlid fishes evolved in East African Lakes Malawi and Tanganyika [10, 11]. In all these cases, convergent phenotypes originated in geographic isolation from each other. Recent theoretical models, however, predict that convergence should be common within species-rich communities [12, 13], such as species assemblages resulting from adaptive radiations. Here, we present the most extensive quantitative analysis to date of an adaptive radiation of cichlid fishes, discovering multiple instances of convergence in body and trophic morphology. Moreover, we show that convergent morphologies are associated with adaptations to specific habitats and resources and that Lake Tanganyika's cichlid communities are characterized by the sympatric occurrence of convergent forms. This prevalent coexistence of distantly related yet ecomorphologically similar species offers an explanation for the greatly elevated species numbers in cichlid species flocks.