Study On Genetic Variation And Introgression Of Mitten Crab In The Minjiang River

Mitten crab, belonging to Eriocheir, is endemic to East Asian, and contains severalimportant economic species, such as Chinese mitten crab (Eriocheir sinensis),Japanese mitten crab (Eriocheir japonicus) and Hepu mitten crab (Eriocheirhepuensis). E. sinensis, a mainly cultured species in China with high economic value,is distributed in most of water body connecting to sea. Eriocheir hepuensis,distrubiting in water body of southern China (e.g. Nanliujiang in Guangxi andZhujiang in Guandong), has been suffered sharply population decline in this decade.The Minjiang River drainage is a hybridizated or introgressed zone for Eriocheirsinensis and Eriocheir hepuensis, which provide a great chance for studying thegenetic variation and introgression of mitten crab. In this study, we studied geneticvariation and introgression of mitten crab in Minjiang River and discussed the geneticevolution of Eriocheir sinensis and Eriocheir hepuensis by combining with,phenotype traits, mitochondrial DNA markers and microsatellite molecular markers.1. Analysis between differentiation in phenotype traits and differentiation atneutral molecular markers of Mitten crab in Minjiang RiverDifferentiation in phenotypic traits (PST) and Differentiation at neutral molecularmarkers (FST) across populations have been become one of important researchingtopics in evolutionary biology In this section, comparison and analysis wereconducted between PSTin14phenotypic traits and FSTin six microsatellite markersfrom133individuals of mitten crab sampled in the Minjiang in2009and2010. Theresults indicated that11phenotypic traits were significantly different (P<0.01)between the2009and2010populations. Mean expected heterozygosity（HE）of2009populations was significantly higher (P=0.008) than that of2010populations，butmean allele richness (AR), observed heterozygosity（HO）and inbreeding coefficient（FIS）were all non-significant difference (P=0.136-0.675) between2009and2010populations. FSTin microsatellite markers was0.1429between the two years. In the14traits, only one trait (F2) was found with PST<FST, suggesting that stabilizingselection is favoring in trait of F2, the other13traits were PST> FST, suggesting thatdirectional selection is occurring. This study provided a valuable data in studying molecular evolution of mitten crab, and contributed a useful reference in comparingPSTand FSTin other aquatic organisms.2. Study on genetic introgression of mitten crab in Minjiang RiverWe carried out the combined analysis of phenotype trait, mitochondrial cytochromeoxidase I subunit (COI) and microsatellite markers in this section. No obviousdifferences were found in genetic diversity parameters (e.g. numbers of polymorphicsites, gene diversity, nucleotide diversity, allelic richness, observed heterozygosity、expected heterozygosity and inbreeding coefficient) between the two years (2009versus2010), and among four populations (Eriocheir sinensis in2009and2010,Eriocheir hepuensis in2009and2010). However, significant genetic differentiationand divergence were found between the two years (2009versus2010). there weresignificant genetic differentiation and divergence between Eriocheir sinensis andEriocheir hepuensis in COI gene but not in phenotype traits and SSR markers analysis.Meanwhile, significantly positive selection pressure was not detected in all mittencrab, suggesting the mitten crab in the Minjiang River is under balanceing selection innatural condition. There were obvious introgression between Eriocheir sinensis andEriocheir hepuensis in the Minjiang River. Alternately, Eriocheir sinensis hasrelatively light introgressed into Eriocheir hepuensis populatotion and Eriocheirhepuensis has relatively high introgressed into Eriocheir sinensis ipopulations.