LAUSR

The fiddler crab Tubuca arcuata (Crustacea: Ocypodidae: Gelasiminae) is widely distributed across East Asia and northern Vietnam. Particularly, this species inhabits estuarine mangroves and mudflats of the East Asian continent, as well as the main islands of Japan and the Ryukyus. By comparing sequences of the mitochondrial 16S, cytochrome oxidase subunit I (COI), and control region genes, two main clades of this species were elucidated. The northern (N) clade was mostly restricted to the region north of the Taiwan Strait, whereas the wide (W) clade could be found throughout the entire range inhabited by this species. Based on the distribution of the ancestral haplotypes of COI and the divergence time of the two clades, our findings suggest that the land bridge barrier present in the Taiwan Strait during glaciations might have played an important role in their cladogenesis, approximately 0.93 million years ago. Here, we propose that the distribution of the ancestral haplotype of the W clade in the Ryukyus and the main islands of Japan was determined by the Paleo-Kuroshio Current, whereas the modern distribution pattern is shaped by the modern Kuroshio Current and other warm currents during the crab reproduction season in the summer.