Signatures of convergence in Neotropical cichlid fish.

ABSTRACT

Convergent evolution of similar phenotypes suggests some predictability in the evolutionary trajectories of organisms, due to strong and repeated selective pressures, and/or developmental constraints. In adaptive radiations, particularly in cichlid fish radiations, convergent phenotypes are commonly found within and across geographical settings. Cichlids show major repeated axes of morphological diversification. Recurrent changes in body patterns reveal adaption to alternative habitats, and modifications of the trophic apparatus respond to the exploitation of different food resources. Here we compare morphologically and genetically two Neotropical cichlid assemblages, the Mexican desert cichlid and the Nicaraguan Midas cichlid, with similar polymorphic body and trophic adaptations despite their independent evolution. We found a common morphological axis of differentiation in trophic structures in both cichlid radiations, but two different axes of differentiation in body shape, defining two alternative limnetic body patterns. Adaptation to limnetic habitats implied regulation of immune functions in the Midas cichlid, while morphogenesis and metabolic functions in the desert cichlid. Convergent phenotypic adaptions could be associated to divergent gene regulation.