Genetic structure and diversity of the island-endemic freshwater prawn Macrobrachium shokitai Fujino & Baba, 1973 (Decapoda: Caridea: Palaemonidae) on Iriomote Island, Ryukyu Archipelago, southern Japan

Iriomote Island is a small continental island hosting approximately 40 rivers characterized by short, steep-gradient streams and small waterfalls. We examined the population genetic structure and diversity of the freshwater prawn Macrobrachium shokitaiFujino & Baba, 1973 (Palaemonidae) using the mitochondrial cytochrome c oxidase subunit I (COI) gene sequence. Specimens were collected from 19 sites along ten rivers on the island, covering the known geographic distribution of the species. Haplotype and nucleotide diversities were very low within each river on the island. Nearly all haplotypes were exclusive to a given river, confirming distinct population structures among rivers at a small geographical scale. Slight genetic differentiation was discerned between the upper and lower sites of waterfalls in only the Yuchin River. Phylogenetic tree reconstruction, haplotype network, and principle coordinate analysis classified five clades roughly correspond to geographical groups in the western, southern, central, and northern regions of the island. Extreme caution should therefore be taken when translocating individuals to other rivers to avoid introducing genetic disturbance, even during conservation and mitigation efforts.