Tracing Ancient Migration Routes: Did Gloydius Pitvipers Disperse Across Paleo-Tibet Through Temperate and...

The Himalayan-Tibetan orogen has undergone complex paleoenvironmental transformations that shaped its biodiversity, yet the timing and sequence of surface uplift-and corresponding biogeographic scenarios for endemic Himalayan taxa-remain debated. We investigated the biogeographic history of Gloydius pitvipers (Serpentes: Crotalinae) from the Himalaya and Hindu Kush by integrating a time-calibrated mitochondrial phylogeny with paleoclimatic reconstructions and species distribution modeling. Our results suggest that Gloydius originated in East and Southeast Asia during the early Miocene (~18.6 Ma), with divergence of the Himalaya-Hindu Kush clade at ~14.5 Ma and subsequent diversification from ~11.7-6.9 Ma. Phylogenetic patterns suggest that ancestral lineages expanded westward across paleo-Tibet via subtropical to warm-temperate corridors, likely through a Central Paleo-Trans-Tibet Valley between the Gangdese and Tanggula Mountains, rather than along the Himalayan arc. A secondary corridor along the Indus-Yarlung Suture Zone may have allowed access to Himalayan transverse valleys, facilitating colonization of the western and central Himalaya, while the eastern Himalaya remained unoccupied despite suitable climate. Paleoclimatic models reveal dynamic habitat shifts over the last 3 million years, highlighting the sensitivity of these low-dispersal taxa to climatic fluctuations. This study provides a plausible scenario for the paradoxical phylogenetic topology of Himalayan Gloydius, offering a biogeographic model for disjunct trans-Tibet distributions of poorly dispersing taxa and a biotic perspective on the Miocene tectonic and environmental evolution of the Himalayan-Tibetan Orogen.