Neotropical Riverine Cichlids: Adaptive Radiation and Macroevolution at Continental Scales

Abstract

Neotropical cichlids include over 550 species from Central and South America and the Caribbean and are increasingly recognized as models for studying evolutionary diversification. Cichlinae’s great morphological, ecological, and behavioral diversity is concentrated in the tribes Geophagini, Heroini, and Cichlasomatini. Feeding and swimming morphology broadly fit two gradients of ecomorphological differentiation: An “elongation axis” follows a ram–suction feeding gradient of deep-bodied fishes with diverse diets at one end and mostly predatory shallow-bodied taxa at the other end. Body and fin configurations correspond with habitats spanning open substrate to structured areas. A second gradient of morphology spans suction feeders and biters with benthic-feeding or complex three-dimensional habitats. Several body configurations reflect specializations to live in rapids. Rates of Cichlinae ecomorphological disparity and lineage diversification often showed early, rapid acceleration followed by a slowdown. Early divergence in South America was likely dominated by the radiation of Geophagini. Rapid geophagin diversification into new niches may have precluded divergence in other South American cichlids, particularly Heroini and Cichlasomatini. Further lineage and morphological divergence in Heroini increased after colonization of Central America. Cichlinae appear to have repeatedly radiated by taking advantage of ecological opportunity in novel environments across the Neotropics, resulting in widespread convergence.