Abstract
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.