What Determines the Distinct Morphology of Species with a Particular Ecology? The Roles of Many-to-One Mapping and Trade-Offs in the Evolution of Frog Ecomorphology and Performance.

Organisms inhabiting a specific environment often have distinct morphology, but the factors that affect this fit are unclear when multiple morphological traits affect performance in multiple behaviors. Does the realized morphology of a species reflect a compromise in performance among behaviors (i.e., trade-offs)? Or does many-to-one mapping result in morphological distinctness without compromising performance across behaviors? The importance of these principles in organismal design has rarely been compared at the macroevolutionary scale. Here I study 191 species of frogs from around the world that inhabit different microhabitats, using models of phenotypic evolution to examine how form-function relationships may explain the fit between ecology and morphology. I found three key results. First, despite being distinct in leg morphology, ecomorphs were similar in jumping performance. Second, ecomorphs that regularly swim showed higher swimming performance, which paralleled the higher leg muscle mass in these taxa. Third, many-to-one mapping of form onto function occurred at all but the highest levels of both jumping and swimming performance. The seemingly contradictory first two results were explained by the third: when one behavior occurs in all species while another is restricted to a subset, many-to-one mapping allows species with distinct ecologies to have distinct body forms that reflect their specialized behavior while maintaining similar performance in a more general shared behavior.