Phylogeographic Structuring of the Kuroshio-Type Prawn Macrobrachium japonicum (Decapoda: Palaemonidae) in Taiwan and Ryukyu Islands

Oceanic currents, biological traits, and geological evidence from historical climate change have shaped the distribution of genetic diversity and demographic history in Macrobrachium japonicum. In this study, we investigated the phylogeographic structures and demographic history of M. japonicum in Taiwan and the Ryukyu Islands by the partial mitochondrial COI gene. The topology of the haplotype minimum-spanning network revealed a star-like structure, which suggested a recent range expansion. With the apparent lack of strong dispersal barriers to gene flow between ocean basins, amphidromous prawns, as marine organisms with larvae of high dispersal abilities, are generally expected to show genetic homogeneity. Divergence data suggested that M. japonicum populations diverged 0.462 ± 0.164 myr. Complex patterns of asymmetrical gene flow indicate that variation in dispersal ability is affected by the dominant Kuroshio Current systems of the Pacific Ocean. Analysis of its demographic history revealed that M. japonicum underwent a decline in size following a recent population expansion based on ABC analysis. Bayesian skyline plot analyses of all populations indicated that the expansion of M. japonicum was estimated to have occurred in 175 Kya and that the effective population size rapidly increased by approximately 50 Kya. The results of this study may offer both practical and theoretical value for the further study of conservation genetics, management, and sustainable resource utilization.