Variation, plasticity and modularity in anuran development

Although anuran development is generally thought to be relatively conservative, a great deal of variation is evident when different species are compared. This report summarizes the results of comparative analyses of different aspects of anuran development. These include differences in sequence and timing of developmental events, the effects of genome size, and the effects of different life history strategies on anuran embryogenesis. The results show that anuran development is plastic at the evolutionary level, and many changes can occur in the developmental processes of anurans throughout their evolution. Changes are apparently rapid, and are as common as cladogenic events. This evolutionary plasticity can be attributed to the modular nature of anuran development. Different modules can shift relative to one another in time or in space, creating variations in the observed developmental patterns. However, shifts in modules can occur even without having a significant effect on the ultimate outcome of the process. I discuss the implications of the modular nature of development on the evolution of anuran development, and of the group in general.