Population divergence of the sentinel crab Macrophthalmus banzai is consistent with regional breeding season differences.

We compared the breeding season and genetic population structure of six sentinel crab (Macrophthalmus banzai) populations in southwestern Japan. Ovigerous females from Northern group populations (Wakayama, Kochi, and Tanega-shima) were observed from March to September, whereas ovigerous females from Southern group populations (Amami-oshima, Okinawa-jima, and Iriomote-jima) were observed from October to May. Genetic analysis using two markers corresponding to mitochondrial DNA encoding cytochrome oxidase subunit I (COI) and the large subunit of ribosomal RNA (16Sr-RNA) revealed a marked genetic difference between the Northern and Southern groups. A genetic boundary exists between the Tanega-shima and Amami-oshima populations, which is consistent with the interpopulation difference in the breeding season.