Genetic Differences And Introgression Of Mitten Crabs In Northeast Asian Region

The mitten crabs, Eriocheir sensu stricto, including Chinese mitten crab(Eriocheir sinensis), Japanese mitten crab(Eriocheir japonicus)and Hepu mitten crab(Eriocheir hepuensis),which are the most economically significant species in East Asian region, are widely distributed in China, Korea, Japan and eastern Russia. It is reported that Vladivostok locating in Far East Russia is a sympatric zone for E. sinensis and E. japonicus, providing a good conditions for studying the genetic difference and introgression of mitten crab in Northeast Asian region. In this paper, based on morphological and molecular datasets, we studied genetic variation of the mitten crab distributing two representative important areas(Tumenjiang River and Vladivostok) in the Northeast Asia by using mitochondrial DNA and microsatellite markers. The aims of this study are to examine direction and extent of introgression between Chinese and Japanese mitten crab in the Northeast Asia region, meanwhile, to provide insight into evolutionary introgression and biogeography of other organisms in Northeast Asia. The detailed results of the study are presented as follows:1 、 Morphological differences and genetic admixture of mitten crabs in the Tumenjiang RiverThe Tumenjiang River is an international river linking China, the Democratic People’s Republic of Korea, and Russia. However, there has been little researches on the mitten crab in this river. In present study, mitten crabs were sampled in the Tumenjiang River and their morphological traits and gonad situation were compared with other populations of Chinese mitten crab(Eriocheir sinensis) sampled in the Yellow River and Liaohe Rivers and with the Japanese mitten crab(Eriocheir japonicus) collected on the Japanese mainland. Thirty-two morphological traits were examined with three kinds of multivariate analysis and a genetic cluster analysis. A discriminant analysis identified the lowest accuracy of discrimination among the Tumenjiang River crabs(83.30%). A principal components analysis revealed that the 12 largest differences in morphological traits in the Tumenjiang River population were between E. sinensis and E. japonicus. A traditional clustering analysis showed the smallest differences between the Tumenjiang River crabs and the Japanese crabs. The results of a genetic clustering analysis also revealed that 60% of the individual crabs in the Tumenjiang River clustered with E. japonicus, whereas only 10% of individuals clustered with E. sinensis, and the remaining 30% of individuals may have been an introgression type. These results indicate that the mitten crab population in the Tumenjiang River comprises overlapping distributions or a genetically mixed population of E. sinensis and E. japonicus, and that its morphological traits are closer to those of E. japonicus than to those of E. sinensis. The results of histological observation of ovary and testis of mitten crab showed the consistent gonadal development stage of mitten crabs between the Tumenjiang River in May and the Yellow, Liaohe Rivers in October, which revealed some mitten crabs in the Tumenjiang River would reach mature stage in the third year.2 、 Genetic relationship and selection pressure analyses of mitten crab in the Northeast Asian region.In this paper, genetic relationship and selection pressure were analyzed for mitten crab from the Tumenjiang River and Vladivostok and their adjacent regions in the Northeast Asian based on mitochondrial ND2 gene. The results showed the mitten crab sampled in the Tumenjiang River exhibited 63.3% frequence of mt DNA haplotype with E. sinensis and 36.7% with E. japonicus, and the mitten crab sampled in the Vladivostok exhibited 71.9% frequency of mt DNA haplotype with E. sinensis and 28.1% with E. japonicus. Nucleotide diversity in the Tumenjiang population(π=0.0133) and Vladivostok(K=0.0160) and average number of nucleotide differences in this two location(9.097 and 10.943, respectively) were higher than those of E. sinensis(π=0.0022, K=1.500) in China and E. japonicus( π =0.0028, S=1.920) in Japan, meanwhile, genetic distance within population in the Tumenjiang River and Vladivostok were higher than that in the E. sinensis and E. japonicus, indicating genetic introgression and admixture of mitten crab the Tumenjiang River and Vladivostok region. Cluster analysis showed that some individuals from the Tumenjiang River and Vladivostok clustered into E. sinensis lineage, and the reminding clustered into E. japonicus lineage. Significant positive selection was not detected in all mitten crab populations in the Northeast Asian. The present results showed genetic admixture between E. sinensis and E. japonicus in the Northeast region.3、Genetic differences and introgression of the nuclear DNA of mitten crabs in Northeast Asian regionThere is a overlap zone for E. sinensis and E. japonicus in northeast Asian region. However, the degree of admixture of the two species is not known. In this chapter, the level of admixture of the two mitten crab in the Tumenjiang River and Vladivostok was analyzed by microsatellite markers. The results showed that the genetic relationship between mitten crabs in the Tumenjiang River and Vladivostok was relatively close and moderate. Furthermore, the results revealed that the mitochondrial DNA haplotypes of E. sinensis were shared by some individuals of the crabs in the Tumenjiang River and Vladivostok which clustered with E. japonicus, and the mitochondrial DNA haplotypes of E. japonicus were also shared by those clustered with E. sinensis based on STRUCTURE genetic clustering analysis and mitochondria DNA. The results indicated that hybridization and introgression of E. sinensis and E. japonicus lay in the Tumenjiang River and Vladivostok, and a high probability happened in the introgression of E. japonicus. Further analysis of NEWHYBRIDS revealed that mixed individuals of F2-generation and F2-generation backcrossing E. japonicus were existed in the Tumenjiang River and Vladivostok, where the proportion of mixed individuals was 30.00% and 31.25%, respectively. The above results showed that the introgression between E. sinensis and E. japonicus was existed in the Tumenjiang River and Vladivostok, and a high probability was in the introgression of E. japonicus and the proportion of mixed individuals was relatively close.