Comparative phylogeography of two marine species of crustacean: Recent divergence and expansion due to environmental changes

• Opening of the Sea of Japan contributed to divergence of Eriocheir populations.
• The formation of Taiwan Island deepened population divergence of marine species.
• O. oratoria along the China Sea originated from two ancestral populations.
• E. japonica in northwest Pacific Ocean originated from one oldest population.

Environmental changes, such as changes in the coastal topography due to Eurasian plate movements, climate oscillation during the Pleistocene, and alteration of ocean currents, have complicated the geographical structure of marine species and deepened their divergence between populations. As two widely distributed species of crustacean (Oratosquilla oratoria and Eriocheir japonica), weak differences were expected due to their high dispersal potential of planktonic larvae with ocean currents. However, results showed a significant genetic divergence between north of China and south of China in the study. In addition, the estimated north–south divergence time (27–30.5 Myr) of mantis shrimp was near the time of the Himalayan movement, and the China–Japan clade divergence time (10.5–11.9 Myr) of mitten crabs was also coincident with the time of the opening of the Sea of Japan. Thus, we hypothesized that environmental changes in the coastal topography contributed to the marine species divergence. Furthermore, based on phylogenetic analysis, network analysis and haplotype distribution, we surmised that mitten crabs originated from a population with the oldest haplotype (H6) and then divided into the north and south populations due to the recent Eurasian plate movements and ocean currents. And lineage of Japan originated from the north population for the opening of the Sea of Japan. While O. oratoria was guessed to originate from two separate populations in the China Sea. The results of “star-like” network, negative values in neutral test, and Tajima's D statistics of two marine species supported a recent rapid population expansion event after the Pleistocene glaciations.