Historical Patterns of Developmental Integration in Piranhas

TO test the hypothesis that developmental integration coordinatesevolutionary change through history, we dissect the spatialand temporal integration of ontogenetic allometries of piranhabody form and examine the evolutionary coordination among ontogeneticfeatures by a phylogenetic analysis. Few of our characters provideevidence in support of the hypothesis. In general, we find thatdevelopmental integration is historically labile, being modifiedat virtually every speciation event. Most of the ontogeneticfeatures are dissociated in their phylogenetic changes and evolvein a mosaic fashion. Indeed, developmental integration is solabile that primitively integrated features of ontogeny usuallyevolve subsequently as independent characters. Evolutionarychanges in developmental integration can result in increasedor decreased integration on the ontogenetic time scale. Whenlocalized features are deleted from ontogeny, or when spatiallyintegrated features are gained, the derived ontogenies may bemore integrated in a spatial sense. The end result of phylogeneticdissociations may be a more highly developmentally integratedontogeny. Thus, in the piranhas we studied, we find a historicallycoupled increase in developmental integration caudally and adecrease indevelopmental integration cranially.