Phenotypic plasticity, canalization, and the origins of novelty: Evidence and mechanisms from amphibians.

A growing number of biologists have begun asking whether environmentally induced phenotypic change--'phenotypic plasticity'--precedes and facilitates the origin and canalization of novel, complex phenotypes. However, such 'plasticity-first evolution' (PFE) remains controversial. Here, we summarize the PFE hypothesis and describe how it can be evaluated in natural systems. We then review the evidence for PFE from amphibians (a group in which phenotypic plasticity is especially widespread) and describe how phenotypic plasticity might have facilitated macroevolutionary change. Finally, we discuss what is known about the proximate mechanisms of PFE in amphibians. We close with suggestions for future research. As we describe, amphibians offer some of the best support for plasticity's role in the origin of evolutionary novelties.