Data from: Baby fish working out: an epigenetic source of adaptive variation in the cichlid jaw

Understanding the developmental processes that underlie the production of adaptive variation (i.e., the “arrival of the fittest”) is a major goal of evolutionary biology. While most evo-devo studies focus on the genetic underpinnings of adaptive phenotypic variation, factors beyond changes in nucleotide sequence can also play a major role in shaping developmental outcomes. Here we document a vigorous but enigmatic gaping behavior during early development of Lake Malawi cichlid larvae. The onset of the behavior precedes the formation of bone, and we predicted that it might influence craniofacial shape by affecting the mechanical environment in which bone develops. Consistent with this, we found that both natural variation and experimental manipulation of this behavior induced differential skeletal development that foreshadows adaptive variation in adult trophic morphology. In fact, the magnitude of difference in skeletal morphology induced by these simple shifts in behavior was similar to those caused by genetic factors. Finally, we demonstrate that this mechanical load-induced shift in skeletal development is associated with differences in ptch1 expression, a gene previously implicated in mediating between-species differences in skeletal shape. Our results underscore the complexity of development, and the importance of epigenetic (sensu Waddington) mechanisms in determining adaptive phenotypic variation.