Glaciation-based isolation contributed to speciation in a Palearctic alpine biodiversity hotspot: Evidence from endemic species.

Organisms are unevenly distributed on earth and the evolutionary drivers of that have puzzled ecologists and evolutionary biologists for over a century. Even though many studies have focused on the mechanisms of unevenly distributed fauna and flora, there remains much to learn about the evolutionary drivers behind biodiversity hotspots. In the Tibetan Plateau and Hengduan Mountains, a biodiversity hotspot in the Palearctic realm, alpine uplift cannot be the driver for recent speciation (<two million years ago), researchers broadly refer to climatic oscillations driven biodiversity, however, the specific individual roles of glaciation and inter-glaciation periods in promoting biodiversity is unclear. The current study focuses on investigating whether recent speciation between two close-related avian species (White eared pheasant, Crossoptilon crossoptilon and Tibetan eared pheasant, C. harmani) was driven by glaciation-based isolation or by dispersal during inter-glaciation. To answer this question, we combined Sanger sequencing and next-generation sequencing technology to estimate population structure, phylogeny, divergence time, demographic history and potential historical distributions for C. crossoptilon and C. harmani, which are endemic to China. We found that the divergence time between these two species and within C. crossoptilon are both during glaciation periods. During glaciation periods, both C. harmani and C. crossoptilon experienced isolated distributions and extreme bottlenecks. The results of this study suggest that glaciation-based isolation contributed to recent speciation in the Tibetan Plateau and Hengduan Mountains, and sheds light on our understanding of the evolutionary mechanisms that contributed to the formation of Palearctic alpine biodiversity hotspots and unevenly distributed species richness pattern.