EVOLUTION OF FACULTATIVE PEDOMORPHOSIS IN SALAMANDERS

In some salamander species the retention of larval characteristics in sexually mature adults (paedomorphosis) is an alternative to metamorphosis. In many species paedomorphosis is facultative, thus offering a unique opportunity to test predictions on the evolution of life history variation. Here I expand upon a previous hypothesis (''paedomorph advantage'') and present two alternative selection mechanisms (''best of a bad lot'' and ''dimorphic paedomorph'' hypotheses) for the maintenance of facultative paedomorphosis. Each hypothesis makes specific predictions regarding the environmental conditions favoring paedomorphosis, the resulting larval growth patterns, and the fitness consequences to each morph. I evaluate each hypothesis by testing these predictions using published data. No study has conclusively determined the relative fitness of paedomorphs and metamorphs, which limits our understanding of the evolution of this polymorphism. Larval growth patterns suggest, however, that both the paedomorph advantage and the best of a bad lot hypotheses are viable alternatives for the evolutionary maintenance of facultative paedomorphosis in different species. Thus current data on facultative paedomorphosis support the premise that selection can favor the production of an environmentally induced polymorphism through more than one mechanism.