Studies On The Genetic Variation And Cross Breeding In Four Populations Of Portunus Trituberculatus

Genetic variation of Portunus trituberculatus was analyzed using multianalysis and DNA Sequencing technique. And the cross breeding among wild populations of P.trituberculatus was studied. The main results were shown as follows:Mitochondrial 16S rRNA gene and COⅠgene fragments were amplified and sequenced from 4 wild populations of Portunus trituberculatus. Respectively, 524bp and 658bp long partial gene fragments of the 16S rRNA gene and the COⅠgene were obtained. A high percentage of A+T base composition in the two sequences was observed, which was similar to the results of studies on drosophila, shrimp, crab and other invertebrates. Little sequence variation was observed in 16S rRNA gene and COⅠgene fragments within species. 2 haplotypes were identified from 16 samples with 1 variation site of 16S rRNA gene and 5 haplotypes were identified from 16 samples with 4 variation sites of COⅠgene. In addition, the phylogenetic relationship among several genera of Portunidea was discussed using Eriochier sinensis as the out-group. The molecular phylogenetic trees were constructed by NJ method using software MEGA4.0, and Portunus was clustered with Callinectes first, then they were clustered with Charybdis,and finally with Eriochier sinensis. The results are consistent with classical taxonomy.Portunus trituberculatus is an economically valued crab species. However, rapid expansion in agro-industry of it in recent years in China yielded also some problems such as frequent diseases outbreak, breed/strain degeneration, and natural resource depletion. They have limited the sustainable development. In this research,matings and crosses within and among three different geographical populations(Zhoushan:ZS; Laizhou Bay:LZ; and Haizhou Bay:HZ)of the species were screened for new breed and strains.Seven populations of first filial generations have been obtained,of which three were of matings and 4 crossings.The characteristic indices of the first filial generations were measured on Days 80,100and 120.Results show that the heterosis was significant in the whole carapace width,carapace width,carapace length,body height,and body weight;for instance, the difference in heterosis of Day 80 one was 0.24%—13.50%. The heterosis in LS was greater than in ZL in all dimensions. On Day 100, the heterosis varied -0.88%—4.13% with hybrid weak ness in carapace length. On Day 120, the heterosis varied -1.91%—4.37% with hybrid weakness in carapace length and carapace width. Analysis with ANOVA program shows that some traits were significantly different among seven populations of the first filial generations. Hybridization was proved important in this study for increasing the growth performance of trituberculatus.Five morphological characters of populations of four selected Portunus trituberculatus from Haizhou Bay, Laizhou Bay, Liaodong Bay and Zhoushan were analysed by clustering,discriminant methods and One-Way ANOVA .Crabs from Haizhou Bay and Zhoushan were pooled into one group while crabs from Liaodong Bay and Laizhou Bay were pooled into another group by cluster analysis. In discriminant analysis,The accuracy rate of discriminant on four farmed Portunus trituberculatus from Haizhou Bay, Laizhou Bay, Liaodong Bay and Zhoushan were 80%,76.7%,80% and 42.9%.Total accuracy rate of discriminant was 70.3%. The discriminant functions of the populations from four populations were established,respectively. One-Way ANOVA was conducted on 4 proportional parameters. The results showed that the four proporational parameters were significantly different among the four populations. In this study all results supported that there were some morphological differences among the four populations, but variations of all the morphologieal traits were not characterized subspecies.