Genetic patterns in peripheral marine populations of the fusilier fish Caesio cuning within the Kuroshio Current

AIM: Mayr's central‐peripheral population model (CCPM) describes the marked differences between central and peripheral populations in genetic diversity, gene flow, and census size. When isolation leads to genetic divergence, these peripheral populations have high evolutionary value and can influence biogeographic patterns. In tropical marine species with pelagic larvae, powerful western‐boundary currents have great potential to shape the genetic characteristics of peripheral populations at latitudinal extremes. We tested for the genetic patterns expected by the CCPM in peripheral populations that are located within the Kuroshio Current for the Indo‐Pacific reef fish, Caesio cuning. METHODS: We used a panel of 2,677 SNPs generated from restriction site‐associated DNA (RAD) sequencing to investigate genetic diversity, relatedness, effective population size, and spatial patterns of population connectivity from central to peripheral populations of C. cuning along the Kuroshio Current. RESULTS: Principal component and cluster analyses indicated a genetically distinct lineage at the periphery of the C. cuning species range and examination of SNPs putatively under divergent selection suggested potential for local adaptation in this region. We found signatures of isolation‐by‐distance and significant genetic differences between nearly all sites. Sites closest to the periphery exhibited increased within‐population relatedness and decreased effective population size. MAIN CONCLUSIONS: Despite the potential for homogenizing gene flow along the Kuroshio Current, peripheral populations in C. cuning conform to the predictions of the CCPM. While oceanography, habitat availability, and dispersal ability are all likely to shape the patterns found in C. cuning across this central‐peripheral junction, the impacts of genetic drift and natural selection in increasing smaller peripheral populations appear to be probable influences on the lineage divergence found in the Ryukyu Islands.