Exploring phenotypic diversity: a comparative analysis of cichlid convergence

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. There are some main axes of cichlid 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 two Neotropical cichlid assemblages, the Mexican desert cichlid, and the Nicaraguan Midas cichlid, with similar polymorphic body and trophic apparatus patterns despite their independent evolution and evaluate morphological and gene expression convergence and divergence. We found a single morphological axis of differentiation in pharyngeal jaws with equivalent papilliform and molariform morphotypes in both cichlid radiations. In contrast, we found two different axes of differentiation in the shape of the body, defining two alternative limnetic body patterns. Genetic differences between morphotypes seem to be specific to each radiation, with no clear patterns of convergence.