Parallel evolution of nonfeeding larvae in echinoids

The switch from feeding to nonfeeding larvae is an ecologically important transformation that has evolved on several separate occasions within the echinoids. In each case, this life history transformation has been accompanied by extensive changes in larval morphology. A phylogenetic approach is used here to reconstruct these morphological changes, to begin asking why they have taken the particular forms observed, and to assess the degree of parallel transformation in separate cases. Both traditional character mapping and a less usual aggregate analysis indicate massively parallel transformations in larval morphology associated with, and only with, this particular life history transformation. Some of these parallel morphological transformations may be due to relaxed functional constraints associated with the ancestral life history mode, but many are probably the result of new functional constraints associated with the derived mode. The comparative data suggest a simple and testable model for the switch from feeding to nonfeeding larvae involving three sequential steps.