Phylogeography of an insect inhabiting 'Sky Islands': the relationships among genetic structures and geographical characteristics, geohistorical characteristics, and cyclical climate changes

When gene flow has been restricted between populations, the genetic structure of such species often reflects geohistory and climate changes. Populations of species inhabiting high-altitude regions, known as 'Sky Islands', are isolated and exhibit restricted gene flow, so they often have habitat-specific genetic structures that correspond to their surrounding geographical structures. Here we focus on a limnephilid caddisfly, Rivulophilus sakaii, which inhabits the alpine zone of Japan. Phylogenetic analyses were conducted based on the mtDNA COI and 16S rRNA regions, and the nDNA 18S rRNA, 28S rRNA, CAD, EF1-alpha, and POL-II regions; the results indicated three phylogeographically differentiated intraspecific lineages. Haplotype network and demographic analyses based on the mtDNA COI region suggested the size of the respective isolated populations has stabilized. This suggests that mountain formation in the Japanese Archipelago due to volcanic activity has resulted in barriers to migration and dispersal between high-altitude aquatic insect populations. This was inferred to be an effect of Quaternary climate changes that caused vertical distributional shifts following mountain formation, resulting in repeated connection and fragmentation of the populations. This is important supporting information with regard to discussing the effects and functions of geohistory and climatic changes on the phylogenetic evolution of organisms presently inhabiting interglacial 'Sky Islands'.