Meeting Abstract
The Neo-Darwinian view of adaptation by natural selection assumes that phenotypic variation is produced randomly with respect to function. However, developmental pathways are often buffered against the effects of mutations such that small changes in the timing of gene expression may generate non-random, functionally viable phenotypes. Here we explore the role of heterochrony in the production of ontogenetic variation and phylogenetic diversity in the neurocrania of Neotropical electric fishes (Gymnotiformes: Teleostei). We assess patterns of shape changes during growth and among adults of different species using landmark-based geometric morphometrics in an explicitly phylogenetic framework. We find the brachycephalic to dolichocephalic axis of neurocranial variance, broadly observed across many vertebrate groups, represents the largest component of shape variance (PC1) in development and evolution. We also find shape changes in the face and braincase regions are more integrated during growth in some taxa, and more modular in others, thereby suggesting tradeoffs in the developmental coordination of these two skull regions. These results suggest that neurocranial evolution in gymnotiform electric fishes is constrained by common genetic and developmental pathways present in all vertebrates, and that this biased production of variation has constrained the evolution of neurocranial morphology along lines of least developmental resistance.
