Comparative phylogeography of Himalopsyche (Trichoptera, Rhyacophilidae) in the Tibeto-Himalayan Region: An assessment of the mountain-geobiodiversity hypothesis

The Tibeto-Himalayan Region is famous for its geography, climatic influence, and exceptional and immense biodiversity. The “mountain-geobiodiversity hypothesis (MGH)” explores the interaction of topography, climate, and biology in the evolution of mountain biodiversity. We tested this hypothesis in the Himalayas and the Hengduan Mountains on a group of caddisflies that are endemic to this region. We investigated one caddisfly species pair from each mountain respectively, each pair containing one species inhabiting high elevation and one inhabiting low elevation. We incorporated genomic and ecological evidence to reveal population structure, demographic history, and potential habitat range dating back to the last glacial maximum (LGM) of each species. The results indicated that in both mountains, the high-elevation species showed strong local differentiation, while the low-elevation species were shaped by hydro-morphology indicating greater regional dispersal activity. Results of demographic history and species distribution modelling supported demographic expansions for all species during the LGM linked to an increase in potential habitats. Caddisfly species in the Himalayas generally exhibited an East-West oriented dispersal. Species from the Hengduan Mountains showed greater connectivity on the North-South orientation, suggesting that species have a higher chance to survive in the Hengduan Mountains by both in-situ displacement (along the elevational gradients) and long-distance dispersal (along the latitudinal gradients) during glaciation. Our study demonstrates that historical geodiversity and climate fluctuations interact and influence the diversification of caddisflies in the Tibeto-Himalayan Region, thus supporting the MGH.