Patterns and rates of ecological diversification among Neotropical cichlid fishes

Abstract

The rapid rise of phenotypic diversity and corresponding ecological roles is an emblematic pattern of cichlid evolution, particularly within clades of the East African Great Lakes. Herein, I evaluate the phenotypic and ecological diversification of Neotropical cichlids through time and among clades using a combination of geometric morphometrics, dietary analysis, and comparative phylogenetic methods. I found that the shape of the lower pharyngeal jaw (LPJ), which is part of a major phenotypic innovation among cichlids (i.e., pharyngognathy), is correlated with dietary patterns among Neotropical cichlids. The evolution of trophic roles such as molluscivory, algivory, and piscivory were associated with modifications in LPJ shape and tooth types. Additionally, LPJ shape evolution was correlated with body shape evolution among Neotropical cichlids; however, this pattern was driven by one of the major lineages (the Heroini) in which the evolution of these traits were highly correlated. This discrepancy among major clades may have arisen due to changes in the adaptive landscape as the Heroini colonized Middle America. Indeed, I detected diversity dependent evolution of LPJ shape following the colonization of Middle America, but not following the colonization of South America. Therefore, dissimilar evolutionary and ecological opportunities provided by the subsequent colonization of South and Middle America likely elicited different constraints during their diversification. Ecosystem-scale colonization events have been similarly important events throughout the evolutionary history of some lineages. I found that following the colonization the Paraná and Uruguay Rivers, distantly related pike cichlids (Crenicichla) diversified in situ and in parallel into similar novel ecomorphs associated with trophic specializations, namely molluscivory, crevice feedings, and periphyton grazing. These results indicate that phenotypic and ecological diversity among Neotropical cichlids has varied dramatically among clades, through time, and in response to ecological opportunities provided by the colonization of new environments.