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.

This article focuses on the population genetic structure and diversity of the freshwater prawn *Macrobrachium shokitai* on Iriomote Island, Japan, using mitochondrial cytochrome c oxidase subunit I (COI) gene sequences. The study found that nearly all haplotypes were unique to individual rivers, indicating strong genetic differentiation and limited gene flow among populations even at small geographic scales, with slight differentiation observed above and below waterfalls in one river. Phylogenetic analyses identified five distinct clades corresponding roughly to geographic regions of the island, reflecting historical geological features and past drainage connections. The findings highlight the importance of avoiding translocation of individuals between rivers during conservation efforts to prevent genetic disturbance. The study also suggests that further research on other endemic freshwater species and the island’s paleogeography could enhance understanding of species differentiation on Iriomote.