Convergent evolution is widely viewed as strong evidence for the influence of natural selection on the origin of phenotypic design. However, the emerging evo-devo synthesis has highlighted other processes that may bias and direct phenotypic evolution in the presence of environmental and genetic variation. Developmental biases on the production of phenotypic variation may channel the evolution of convergent forms by limiting the range of phenotypes produced during ontogeny. Here, we study the evolution and convergence of brachycephalic and dolichocephalic skull shapes among 133 species of Neotropical electric fishes (Gymnotiformes: Teleostei) and identify potential developmental biases on phenotypic evolution. We plot the ontogenetic trajectories of neurocranial phenotypes in 17 species and document developmental modularity between the face and braincase regions of the skull. We recover a significant relationship between developmental covariation and relative skull length and a significant relationship between developmental covariation and ontogenetic disparity. We demonstrate that modularity and integration bias the production of phenotypes along the brachycephalic and dolichocephalic skull axis and contribute to multiple, independent evolutionary transformations to highly brachycephalic and dolichocephalic skull morphologies.
In this manuscript, we study the neurocranial evolution and development of Neotropical electric fishes (Gymnotiformes: Teleostei) using geometric morphometrics. Here, we propose the presence of a developmental bias towards the production of brachycephalic skull shapes that likely resulted in the overwhelming degree of convergent evolution in brachycephalic skull shape as compared to dolichocephalic skull shape. We also find a significant relationship between developmental integration and adult skull shape, with brachycephalic species being more modular in development and dolichocephalic species being more integrated.