Genetic admixture of mitten crabs in the Northeast Asia hybrid zones

Hybridization and genetic admixture in hybrid zones promote phenotypic and genotypic adaptive changes in organisms. Hybrids between Chinese mitten crab ( Eriocheir sinensis ) and Japanese mitten crab ( Eriocheir japonica ) have been reported in the Vladivostok region of Russia. However, the direction and extent of hybridization remains unknown in Northeast Asia. In this paper, genetic variation and admixture were investigated by examining a mitochondrial NADH dehydrogenase subunit II gene ( ND 2) and 10 microsatellite DNA loci in mitten crabs from the Tumen River in China and Vladivostok in Russia. In addition, the adjacent distributions of E. sinensis in China and E. japonica in Japan were analyzed. The Tumen River and Vladivostok were both identified as hybrid zones of E. sinensis and E. japonica . As indicated by ND2 sequences analysis, the mitten crabs in the Tumen River and Vladivostok displayed 5–10 times higher nucleotide diversity and more mixed haplotypes than pure E. sinensis and E. japonica . Meanwhile, approximately 31.25% of the mitten crabs in Vladivostok and 30.00% in the Tumen River were identified as potential hybrids, indicating strong genetic admixture between the two mitten crabs in these hybrid zones. Our results provide quantitative evidence of genetic admixture of E. sinensis and E. japonica in Northeast Asia.