Species Composition Of Genus Scylla And Genetic Diversity Of Scylla Paramamosain (Estampador, 1949) Populations In China

In order to study on the species composition and dominant species in the coastal waters of southeastern China in genus Scylla, 413 individuals were collected from 13 sites and 24 measurements were taken. By morphological comparison, there are 4 species being identified, namely S. serrata, S. tranquebarica , S. paramamosain, S. olivacea. The four species can be distinguished by means of the length and shape of the four frontal spines, with or without inner carpus spine and the polygonal patterning of chelipeds and legs. S. paramamosain is the most dominant and the other three species be found in Hainan waters and Beibu Bay only. The morphological characters and a key to Genus Scylla for 4 species are also given.The sequences of mtDNA COI gene fragment of 4 species of mud crabs: S. serrata (Forsk(?)l,1775), S.tranquebarica (Fabricius, 1798), S.olivavea(Herbst,1796), S.paramamosain(Estampador,l949), collected from the coastal waters of southeastern China were analyzed. The genetic difference means 0.0062 intraspecific, while 0.1413 interspecific. The NJ tree shows that all four species formed reciprocal monophyletic groups. These provide additional conclusive evidence that there are four distinct species of mud crab in China. The genetic distance between dominant species and the known S. paramamosain(GenBank accession number: AY373351) is 0.0013, and 0.1213 between dominant species and the known S.serrata(GenBank accession number: AY373341). The results of sequence analysis, genetic distance, and NJ clustering have proved that the dominant species is S.paramamosain.S. paramamosain, the dominant species, is most widely distributed in the coastal waters of southeast China and commonly occurring in estuarine and mangrove waters. The genetic structure and genetic diversity in 480 individuals including 13 wild populations and 3 cultured ones were analyzed using RAPD and AFLP.By RAPD, the percentage of polymorphic loci among wild populations range from 26.79-38.39%, the effective number of alleles per locus(Ne) range from 1.2473-1.3094, the Shannon's Information index range from 0.1511-0.1888 and the Nei's gene diversity(h) range from 0.1097-0.1372. By AFLP, the percentage of polymorphic loci among wild populations range from 61.45-65.85%, the effective number of alleles per locus(Ne) range from 1.1478-1.2103, the Shannon's Information index range from 0.2360-0.2927 and the Nei's gene diversity(h) range from 0.1503-0.1881. The results of RAPD and AFLP show that the genetic diversity of S. paramamosain is low. G_ST among wild populations of S. paramamosain ranges from 0.0154-0.0512 and 0.0029-0.0669 by RAPD and AFLP respectively. Genetic differentiation index indicates there exists some differentiation among different populations of S. paramamosain, but the differentiation is low. More than 95% of genetic diversity was derived from within the populations.The genetic diversity of 3 cultured and 3 wild populations from the same sites are compared. The percentage of polymorphic loci, the effective number of alleles per locus(Ne), the Shannon's Information index, and the Nei's gene diversity(h) of cultured populations are 40.32%, 1.2693,0.2011,0.1516 respectively. While the wild ones are 41.56%, 1.3966, 0.2083,0.1598 respectively by RAPD. The percentage of polymorphic loci, the effective number of alleles per locus(Ne), the Shannon's Information index, and the Nei's gene diversity(h) of cultured populations are 66.29%, 1.2589, 0.2901, 0.1846 respectively. While the wild ones are 68.68%, 1.2611, 0.2962, 0.1895 respectively by AFLP. The cultured populations are lower than wild ones in genetic diversity. The genetic distance between the cultured and wild populations is 0.0253 and 0.0316 by RAPD and AFLP respectively. The result of Cluster's analysis between the cultured populations and 13 wild populations show that Shantou cultured population is closely related to Shantou wild population, Xiamen cultured population and Fuzhou one are closely related to the Beibu Bay group but not to the local wild populations. The results of genetic distance and Cluster's analysis show that genetic differentiation between cultured and wild populations is also not distinct.