Ecological diversification and phylogeny of emydid turtles

Ecological diversification is a central topic in ecology and evolutionary biology. We undertook the first comprehensive species-level phylogenetic analysis of Emydidae (an ecologically diverse group of turtles), and used the resulting phylogeny to test four general hypotheses about ecological diversification. Phylogenetic analyses were based on data from morphology (237 parsimony-informative characters) and mitochondrial DNA sequences (547 parsimony-informative characters) and included 39 of the 40 currently recognized emydid species. Combined analyses of all data provide a well-supported hypothesis for intergeneric relationships, and support monophyly of the two subfamilies (Emydinae and Deirochelyinae) and most genera (with the notable exception of Clemmys and Trachemys). Habitat and diet were mapped onto the combined-data tree to test fundamental hypotheses about ecological diversification. Using continuous coding of ecological characters showed that lineages changed in habitat before diet, ecological change was most frequently from generalist to specialist, and habitat and diet rarely changed on the same branch of the phylogeny. However, we also demonstrate that the results of ancestral trait reconstructions can be highly sensitive to character coding method (i.e. continuous vs. discrete). Finally, we propose a simple model to describe the pattern of ecological diversification in emydid turtles and other lineages, which may reconcile the (seemingly) conflicting conclusions of our study and two recent reviews of ecological diversification.