Phylogeography of a cool-loving caddisfly: analyses of single nucleotide polymorphisms indicate lowland hybridization and highland isolation

Abstract By assessing the genetic structure and gene flow at the local population level, it is possible to visualize connectivity and barriers to migration and dispersal. We focused on the cold-adapted caddisfly Asynarchus sachalinensis Martynov, 1914 (Trichoptera: Limnephilidae) and conducted phylogenetic analyses based on information from single nucleotide polymorphisms. In addition to the two genetic lineages (groups A and B) detected by mitochondrial DNA analyses in a previous study, we discovered that A. sachalinensis is composed of three genetic groups, including group C, which originated from a hybridization of these previous known lineages. The origin of group C was estimated to be ∼.12 Ma and was evaluated to have a high level of gene flow within the group. We also evaluated gene flow within the same mountain massif, where genetic groups B and C live. The results clearly revealed restricted gene flow between the alpine and sub-alpine zones. These results indicate that previously differentiated populations of A. sachalinensis would have undergone a range shift owing to past climatic changes. However, some populations might have survived in refugia and still exist as populations isolated from others owing to topographic discontinuities and climatic differentiation. Moreover, we suggest that differences in their life cycles maintained lineage differentiation and promoted speciation.