Complex geographic- and habitat-based niche partitioning of an East Asian habitat generalist mayflyIsonychia japonica(Ephemeroptera:Isonychiidae) with reference to differences in genetic structure

We focused on the genetic structure and evolutionary divergence of a typical habitat generalist mayfly, Isonychia japonica, inhabiting rivers widely distributed across eastern Asia. In the Japanese Archipelago, they are distributed across a wide range of environments, including up- and downstream areas in 1 river basin. We analyzed DNA sequences of this mayfly from both the mitochondrial (cytochrome oxidase c subunit I [COI] and 16S ribosomal RNA) and nuclear genomes (Histone H3 and ITS2) of specimens from populations across the eastern Asian region, with emphasis on the Japanese Archipelago. Isonychia japonica is genetically differentiated into 2 major clades (C = continental clade, J = Japanese Archipelago clade). Furthermore, clade J is composed of 2 subclades (clades J-U and J-D). Clade J is separated by environment, with specimens constituting clade J-U occurring in small-scale rivers of the upstream regions and specimens constituting clade J-D occurring in large-scale rivers of downstream regions. Clade J-D further consists of 2 minor subclades that occupy different geographical regions (clades J-DN and J-DS).