Rapid diversification of alpine bamboos associated with the uplift of the Hengduan Mountains

Aim The Hengduan Mountains (HDM) of southwest China is a biodiversity hotspot and harbours one of the world's richest temperate floras. However, the origin and evolution of its biota remain largely unresolved. Here we explore the impact of mountain uplift on the diversification process of biodiversity in this hotspot using alpine bamboos. Location The HDM region, southwest China. Taxon Alpine bamboos. Methods We used ddRAD-seq data from the most complete sampling of alpine bamboos undertaken to date (79% of the species diversity), to investigate their evolutionary history. The ancestral area of these bamboos was reconstructed using a time-calibrated phylogeny in BioGeoBEARS and diversification rates were inferred using BAMM analyses. In addition, the impact of mountain uplift on the divergence of alpine bamboos was evaluated using trait-dependent models of diversification. Results The alpine bamboos were strongly supported as monophyletic, and the relationships within them were robustly resolved. Fargesia was found to be polyphyletic and Yushania was resolved as monophyletic. Alpine bamboos originated outside the HDM region during the late Miocene, and spread to this region in the Pliocene, undergoing a significant acceleration in net diversification, which is temporally congruent with the orogeny. The speciation rate increased with altitude and a high diversification rate, estimated to be 0.75 species per million years, was detected for alpine bamboos distributed in high elevations. Main Conclusions Our study demonstrates that heterogeneous mountain habitats and geographical isolation of alpine bamboos, which have limited dispersal ability, are important drivers for their rapid diversification. This study also highlights the power of complementary analyses in revealing the link between species diversification and past geological changes.