Rates of Evolution in Developmental Processes

Abstract

The tempo and mode of morphological evolution are influenced by several factors, among which evolutionary transformations in developmental processes are likely to be important. Comparing the embryos of extant species in an explicit phylogenetic fram work allows the estimation of minimum average rates of evolution in quantitative developmental parameters. It also allows delineation of the maximum time that complex qualitative transformations in developmental mechanism take to evolve. This paper analyzes rates of quantitative and qualitative developmental evolution using examples drawn primarily from echinoderms. The results demonstrate that rates of developmental evolution can be comparable to rates of morphological evolution. There is no indication that rates of evolution in development are lower for earlier stages, contrary to the prediction of “tree” models of epigenetic interactions. In particular, rates of evolution in oogenesis can exceed rates of evolution in adult body size. Rates of developmental evolution can vary by up to two orders of magnitude within a clade. Whether such large scale variation in evolutionary rates of developmental processes is a general phenomenon can only be answered by further study.