Diversification of freshwater crabs on the sky islands in the Hengduan Mountains Region, China

[Display omitted] •Freshwater crabs were studied on sky islands (SIs) in Hengduan Mountains Region (HMR), China;•Crab phylogeny correlated with past Oligocene uplift of HMR, and SIs emergence;•SIs form cryptic ‘species pumps’ driving speciation in montane freshwater crabs;•Dry-hot valleys between SIs isolated endemic crabs, facilitating local diversification. The numerous naturally-fragmented sky islands (SIs) in the Hengduan Mountains Region (HMR) of southwestern China constitute discontinuous landscapes where montane habitats are isolated by dry-hot valleys which have fostered exceptional species diversification and endemicity. However, studies documenting the crucial role of SI on the speciation dynamics of native freshwater organisms are scarce. Here we used a novel set of comprehensive genetic markers (24 nuclear DNA sequences and complete mitogenomes), morphological characters, and biogeographical information to reveal the evolutionary history and speciation mechanisms of a group of small-bodied montane potamids in the genus Tenuipotamon. Our results provide a robustly supported phylogeny, and suggest that the vicariance events of these montane crabs correlate well with the emergence of SI due to the uplift of the HMR during the Late Oligocene. Furthermore, ancestrally, mountain ridges provided corridors for the dispersal of these montane crabs that led to the colonization of moist montane-specific habitats, aided by past climatic conditions that were the crucial determinants of their evolutionary history. The present results illustrated that the mechanisms isolating SIs are reinforced by the harsh-dry isolating climatic features of dry-hot valleys separating SIs and continue to affect local diversification. This offers insights into the causes of the high biodiversity and endemism shown by the freshwater crabs of the HMR in southwestern China.