Spatial patterns of phylogenetic diversity in the Andean tribe Eudemeae (Brassicaceae) and their association with climatic gradients in western South America

Abstract

The spatial distribution of species and their clades reflects the interaction of different ecological, evolutionary and stochastic processes that shape the current biogeographic patterns of biodiversity. Spatial patterns of alpha and beta phylodiversity can capture different historical processes such as niche conservatism, dispersal, diversification, and extinction, which may have operated over several million years. Eudemeae (Cruciferae) represents a clade of 43 species and 11 genera distributed throughout western South America, from the Northern Andes in Colombia (c. 5°N) to the southernmost portion of the Southern Andes in Argentina and Chile (c. 55°S). In this study, we attempt to elucidate the association between climate and phylodiversity variation in Eudemeae using distributional, climatic and molecular data for a large sample of taxa. Our study showed that beta phylodiversity patterns in Eudemeae are partially explained by climate, with climate tolerance being one of the main factors associated with variation in phylogenetic turnover. In particular, thermal tolerance is associated with turnover of deeper nodes, while aridity tolerance is related to turnover of more recent nodes. Likewise, temperature gradient appears to be associated with higher alpha diversity along the temperate regions of Central and Southern Andes, displaying the tribe an inverse latitudinal gradient in species diversity consistent with the austral niche conservatism hypothesis. In addition, major evolutionary regions showed high levels of climatic/ecological differentiation, and diversity hotspots showed phylogenetic clustering, suggesting that phylogenetic niche conservatism and in situ lineage diversification were dominant processes in the evolution of the tribe.