A license to disperse: climatic niche lability and geographic expansion shape the diversification of Oleaceae

Patterns of species diversity reflect interactions among ecological, biogeographic, and lineage-specific evolutionary processes. Oleaceae provides a useful comparative system because its five tribes differ markedly in species richness, geographic extent, dispersal history, and genomic background. Using distribution data for 476 species and a time-calibrated phylogeny of 283 Oleaceae species spanning all five tribes, we integrated ecological niche modelling, ancestral-range and climatic-niche reconstruction, diversification-rate analyses, and phylogenetic comparative methods while accounting for uneven tribal sampling. Climatic niche position and breadth evolved heterogeneously across Oleaceae, while major range expansions beyond the reconstructed ancestral Asian region were concentrated in Jasmineae and Oleeae. Climatic niche evolution and speciation rates were not consistently coupled; rather, their relationships with dispersal and diversification were lineage- and climatic-axis-specific. Oleeae showed more coordinated associations among niche evolution, dispersal, and speciation, whereas Jasmineae exhibited a more restricted, axis-specific pattern. The ancient whole-genome duplication (WGD) in Oleeae may have contributed to its distinctive evolutionary trajectory. Overall, our results support a conditional 'license to disperse' framework in which climatic niche lability facilitates geographic expansion, thereby indirectly increasing opportunities for diversification.