Species diversification and ecomorphological evolution in the radiation of tanagers (Passeriformes: Thraupidae)

Abstract

Abstract Ecological opportunity is hypothesized to cause an early burst of species diversification and trait evolution followed by a slowdown in diversification rates as niches are filled. Nonetheless, few studies have tested these predictions empirically with ecomorphological data at the large spatial scales relevant to most of biodiversity. Tanagers (Passeriformes: Thraupidae), the largest family of songbirds, show an early burst of species diversification and provide an excellent opportunity to test one of the hallmarks of adaptive radiation: rapid ecomorphological evolution. Here, we test for an early-burst pattern of a resource-exploiting trait (bill morphology) across the radiation of tanagers using a time-calibrated molecular phylogeny and high-resolution three-dimensional surface scans of bill structure from museum study skins. Using recently developed methods of multivariate trait evolution, we find evidence for a rapid burst of bill shape evolution early in the radiation of tanagers, followed by a subsequent decrease in rates toward the present. Likewise, we show that morphological disparity is distributed among (rather than within) subclades, indicating that most of the observed bill shape disparity evolved early in the radiation of tanagers and has slowed through time. The diversification dynamics of tanagers match patterns expected from adaptive radiation and the filling of ecomorphospace.