A Study On The Genetic Diversity In The Wild Population And Cultivate Population Of Sea Cucumber (Apostichopus Jponicus)

Polyacrytamide gel electrophoresis (PAGE) was used to investigate the isozyme genetic variation in two wild and one cultivate populations of Sea cucumber Apostichopus japonicus. 48 individuals were sampled from each populaion including two wild populations: wei hai (WH) and yantai (YT) and one laizhou cultivate population (LZ). Fifteen genic loci were detected by testing 11 isozymes in musle.The result shows: the proportion of polymorphic loci P_0.99 of YZ,WH,YT were 46.7%,33.3% and 46.7%; P0.95 of the three populations are 20%, 20% and 33.3%.The mean observed heterozygosities (H₀) were 0.0786, 0.0800 and 0.1356, while the mean expected heterozygosities (H_e) were 0.1040,0.0924 and 0.1543,respectively.The heterozygous divergent indexes (D) of them are -0.1884,-0.1994 and -0.0986 ,which shows the loss of heterozygotes. From above datum, it could be concluded that although WH and YT are both wild populations, the genetic variation of WH wild population is similar with LZ cultured population, while the YT wild population has higher genetic variation.Fragments from three mitochondrial genes of Apostichopus japonicus in three populations (YT, WH, LZ ) were amplified and sequenced, and 570bp 16S rRNA, 640bp COI and 900bp IrRNA-COI fragments were obtained. Analysis of gene fragments indicated that: 1) two haplotypes were identified in each mtDNA fragment, and the number of accession was from AY852278 to AY852283 in Genbank;2) there was no prominent difference among the three groups and no insertion, deletion or transversions among them except for a few transitions ;3) the mean A+T contents of 16S rRNA, COI and IrRNA-COI gene fragments were respectively 56.2%, 59.2% and 61.8%, which exceeded the contents of G+C; 4) The homology among three groups were from 99.84% to 99.96% ,which showed they were the same species.The sequences of Apostichopus japonicus in our study were compared with that of 8 outgroups coming from Genbank. The results showed that: there were prominentdifference among different orders or families. The sequences of three groups in our study have higher homology with Parastichopus californicus and Parastichopus parvimensis, while they have the significant difference with five groups of Dendrochirotida. All kinds of loci were analyzed by DNAsp software. The results indicated that: there were 324 sites of insertion or deletion, 388 monomorphic sites, 291 polymorphic sites and 243 parsimony informative sites in IrRNA- COI sequence; 1 site of insertion or deletion, 399 monomorphic sites, 241 polymorphic sites and 186 parsimony informative sites in total 641 sites of COI sequence. In the sequences of 16S rRNA, 363 sites of insertion or deletion, 154 monomorphic sites; 125 polymorphic sites; 110 parsimony informative sites were observed. MEGA 2.1 was used to analyze the base composition and genetic distance and construct the NJ and MP phylogenetic trees. The data showed that : the mean A+T contents exceeded the contents of G+C, and the contents of G was lower than other bases. The evolutionary relationship of the 11 groups in phylogenetic NJ and MP tree supported the conclusion in existing morphology taxon. The three groups in our study belonged to the Aspidochirotida Stichopodidae, and they were clustered with Parastichopus californicus and Parastichopus parvimensis at first. The genetic distance also supported the conclusion. The results above affirmed the evolutionary relationship of sea cucumber between our country and other countries.