Fine-scale genome-wide signature of Pleistocene glaciation in Thitarodes moths (Lepidoptera: Hepialidae), host of Ophiocordyceps fungus in the Hengduan Mountains

The Hengduan Mountains region is a biodiversity hotspot known for its
topologically complex, deep valleys and high mountains. While landscape
and glacial refugia have been evoked to explain patterns of inter-species
divergence, the accumulation of intra-species (i.e. population level)
genetic divergence across the mountain-valley landscape in this region has
received less attention. We used genome-wide restriction site-associated
DNA sequencing (RADseq) to reveal signatures of Pleistocene glaciation in
populations of Thitarodes shambalaensis (Lepidoptera: Hepialidae), the
host moth of parasitic Ophiocordyceps sinensis (Hypocreales:
Ophiocordycipitaceae) or "caterpillar fungus” endemic to the glacier
of eastern Mt. Gongga. We used moraine history along the glacier valleys
to model the distribution and environmental barriers to gene flow across
populations of T. shambalaensis. We found that moth populations separated
by less than 10 km exhibited valley-based population genetic clustering
and isolation-by-distance (IBD), while gene flow among populations was
best explained by models using information about their distributions at
the local last glacial maximum (LGML, 58 kya), not their contemporary
distribution. Maximum likelihood lineage history among populations, and
among subpopulations as little as 500 meters apart, recapitulated
glaciation history across the landscape. We also found signals of isolated
population expansion following the retreat of LGML glaciers. These results
reveal the fine-scale, long-term historical influence of landscape and
glaciation on the genetic structuring of populations of an endangered and
economically important insect species. Similar mechanisms, given enough
time and continued isolation, could explain the contribution of glacier
refugia to the generation of species diversity among the Hengduan
Mountains. --