Reconstruction of invasion pathways of East Asian crab species of the genus Hemigrapsus (Decapoda, Brachyura, Varunidae) based on a comparative phylogeographic approach

Abstract Three intertidal varunid crab species of the genus Hemigrapsus , viz. H. penicillatus , H. sanguineus , and H. takanoi , are widely distributed along the East Asian coastline. The first two became globally well-known after their introduction into Atlantic waters of North America and Europe. Since the first record in the late 1980s, they established breeding populations and now live in sympatry with native and other invasive crab species. The aim of this study was to determine the correct species identity and geographic origin of these invasive populations and, if possible, estimate the number of independent invasion events. For that purpose, specimens from the three species were obtained from native populations in Taiwan, Japan, Russia, Korea, and China, and genetically compared to invasive populations from Europe and the U.S.A. Sequences of the mitochondrial cytochrome c oxidase subunit I gene were generated and used for haplotype network and AMOVA analyses, thus providing insights into the potential invasion pathways, gene flow, and phylogeography of the two invasive species. Pronounced geographic structure for all three species is revealed in their native ranges, with a marked differentiation among northern and southern populations. We furthermore provide evidence that all invasions into North America and Europe originated from northern Asian populations, which is in line with similar climatic conditions in Europe, northeastern America and northern Asia. Our results also confirm the recent finding that all European populations previously thought to consist of H. penicillatus should be reclassified as H. takanoi .