Ecological radiation with limited morphological diversification in salamanders.

A major goal of evolutionary biology is to explain morphological diversity among species. Many studies suggest that much morphological variation is explained by adaptation to different microhabitats. Here, we test whether morphology and microhabitat use are related in plethodontid salamanders, which contain the majority of salamander species, and have radiated into a striking diversity of microhabitats. We obtained microhabitat data for 189 species that also had both morphometric and phylogenetic data. We then tested for associations between morphology and microhabitat categories using phylogenetic comparative methods. Associations between morphology and ecology in plethodontids are largely confined to a single clade within one subfamily (Bolitoglossinae), whereas variation in morphology across other plethodontids is unrelated to microhabitat categories. These results demonstrate that ecological radiation and morphological evolution can be largely decoupled in a major clade. The results also offer a striking contrast to lizards, which typically show close relationships between morphology and microhabitat.