Fink, W. L. and M. L. Zelditch

To test the hypothesis that developmental integration coordinates evolutionary change through history, we dissect the spatial and temporal integration of ontogenetic allometries of piranha body form and examine the evolutionary coordination among ontogenetic features by a phylogenetic analysis. Few of our characters provide evidence in support of the hypothesis. In general, we find that developmental integration is historically labile, being modified at virtually every speciation event. Most of the ontogenetic features are dissociated in their phylogenetic changes and evolve in a mosaic fashion. Indeed, developmental integration is so labile that primitively integrated features of ontogeny usually evolve subsequently as independent characters. Evolutionary changes in developmental integration can result in increased or decreased integration on the ontogenetic time scale. When localized features are deleted from ontogeny, or when spatially integrated features are gained, the derived ontogenies may be more integrated in a spatial sense. The end result of phylogenetic dissociations may be a more highly developmentally integrated ontogeny. Thus, in the piranhas we studied, we find a historically coupled increase in developmental integration caudally and a decrease in developmental integration cranially.