Environmental correlates of diversification within the bee genus Melissodes (Hymenoptera: Apidae)

Abstract

For decades, biologists have debated the extent to which extrinsic vs. intrinsic forces drive diversification in various clades. Since the most obvious traits an organism possesses are its intrinsic morphological characters, extrinsic correlates of diversification are often not the focus of model-based evolutionary analyses. However, the environment plays a major role in shaping species turnover, and model-based analyses of the relationships between species turnover and species’ niche characteristics can be conducted just as readily as with intrinsic traits. Here, we examine the connections between bioclimatic variables and diversification in the bee genus Melissodes (Apidae: Eucerini) in a biogeographic context. The evolutionary history of the genus Melissodes is currently not well understood, but it was likely molded by interactions with the environment across its wide distribution. We find that changes in diversification rates over time correlate most strongly with the mean diurnal range and precipitation seasonality in habitats lineages occupy. Interestingly, the subgenera Eumelissodes and Melissodes sensu stricto are the only 2 clades to have high diversification rates near the tips. The remaining 3 subgenera exhibit consistently lower rates since approximately 10 million years ago, possibly due to range contractions. Our study sheds light on relationships between species turnover and external traits in an ecologically and economically important group of pollinators.