Radiations and morphological divergence: complex craniofacial evolution in a diverse group of African electric fishes (Mormyridae)

Abstract The Mormyridae is a species-rich clade of weakly-electric African fishes with ancient phylogenetic origins and high diversity in the shape of the head, snout, and oral jaws. We quantified the diversity of craniofacial morphologies using micro-computed tomography, geometric morphometrics, and phylogenetic comparative methods; then assessed phenotypic evolution in functionally relevant traits likely to be implicated in trophic specialization. We found high levels of phenotypic diversity across the group and documented multiple instances of phenotypic divergence and a single instance of within-family morphological convergence. A single subclade (designated C+ clade) that diversified over the past c. 15 Mya was found to encompass more than half of the mormyrid skull shape diversity. The results show primarily divergent patterns of evolutionary change, in which the phenotypic disparity of functionally distinct skull regions is hypothesized to be influenced by many environmental factors. The biogeographic, temporal, and phenotypic patterns of mormyrid diversification closely resemble expectations of a continental radiation, in which ecological trait diversity accumulates over broad geographic and temporal scales.