Quaternary-related genetic differentiation and parallel population dynamics of the Eurasian Jay (Garrulus glandarius) in the circum-Japan Sea region

The circum-Japan Sea region (CJSR) greatly impacted animal diversity in the Eastern Palearctic during the Quaternary. However, its role in avian diversification has been underestimated because of the high dispersal capabilities of birds over the sea. We investigated the phylogeographic and demographic history of the Eurasian Jay (Garrulus glandarius), focusing on CJSR populations. We sequenced a total of 1744 bp of mitochondrial DNA (cytochrome b and control region) from 73 samples. Together with the database sequences, we reconstructed a phylogenetic tree for the Eurasian Jay over the Palearctic. The earliest phylogenetic divergence was inferred to be related to geological vicariance between the Japanese archipelago and Eurasian mainland around the Pliocene–Pleistocene boundary. Several demographic analyses have suggested that there are two divergent subspecies across the CJSR, G. g. brandtii on the mainland, Sakhalin, and Hokkaido and G. g. japonicus in the archipelago. These simultaneously experienced population contractions to independent refugia and subsequent expansions around the last glacial period, i.e., parallel population dynamics. We suggest that the two landmasses of the CJSR were important for generating and preserving the phylogenetic structure of the Eurasian Jay.