Studies On Biological Traits And Molecular Genetics Based On Mitochondrial DNA Of Potamocorbula

The clams of Potamocorbula with high economic value are widely distributedalong the coastal areas of China. But there is few studies on population genetics andmolecular biology research, most of them were concentrated in the nutrition andbreeding research. Taking wild river blue clams as the material, we firstly explored therelationship between the phenotypic traits and weight of Potamocorbula laevis, andanalyzed its chromosome karyotype. In this study, genetic diversity and classificationstatus of four species of Potamocorbula are also analyzed based on mitochondrial DNACOI and16S rRNA. The two mitochondrial gene fragments were also used to analyzegenetic diversity of three different geographic populations of P. amurensis and P. laevis.The results are as follows:1. The relationship between the phenotypic traits and body weight two shell colorsof P. laevis. Two kinds of wild P. laevis with different shell colors were selected100individuals in each. The shell length, shell width, shell height and live body weight ofthe200individuals were measured and made a statistical analysis with EXCEL andSPSS11.5. The results show that phenotypic values of yellow P. laevis are larger thanthose of brown ones, with highly statistical significance (P<0.01). The correlationanalysis indicated that, the correlation coefficient of phenotypic character and live bodyweight of the yellow P. laevis both reached the extremely significant level (P<0.01), andthe two correlation coefficients of brown P. laevis have reached a significant level(P<0.05). To the yellow individual, the shell length has greatest direct influence on livebody weight, and the shell height influence is minimal. However, to the brownindividuals happen to be opposite. Regression equations of two colors of P. laevisphenotypic traits and live body weight are established through multiple regression analysis, and the ANOVA analysis showed that the equation of yellow P. laevis verysignificantly exists (P<0.01), and the equation of the brown P. laevis is significantlyexisted (P<0.05).2. Chromosome karyotype of P. laevis was analyzed with preparation ofchromosome specimen in conventional method. The result showed that the chromosomenumber of P. laevis was34; and its karyotype formula was2n=34=14m+12sm+8t.There were no acrocentric chromosomes and heteromorphic chromosome.3. Genetic analysis on the sequence fragments of mitochondrial COI and16SrRNA gene from four Potamocorbula. The gene fragments of the mitochondria COI and16S rRNA in P. laevis, P. amurensis, P. ustulata and P. rubromuscula were amplifiedand sequenced. Totally,40sequences of COI gene and16S rRNA were obtained andthey are650bp and450bp in length after trimming，respectively. It showed a low GCbase composition (38.6%). The result of sequence analysis showed that the intraspecificvariation and interspecific variation in16S rRNA were lower than those in COI gene.Ten mutation sites and7haplotypes were detected in the gene fragment sequence of16SRNA. Taking M. arenaria as the out-group, the phylogenetic tree was constructed usingthe method of NJ with the software MEGA4.0. Based on the genetic distance and NJphylogenetic tree，we found that the four speices of Potamocorbula failed to achievesignificant genetic differentiation between species. This result is different from thetraditional classification.4. The genetic diversity of three populations of P. amurensis based onmitochondrial CO I and16S rRNA gene. Mitochondrial COI and16S rRNA genefragments of wild P. amurensis were amplified with universal primer; the PCR productswere sequenced,658bp and441bp nucleotide sequences were obtained. The T, C, A, Gand AT contents in this fragment were45.4%and32.0%、13.5%and13.3%、20.7%and29.3%、20.4%and25.3%、66.1%and61.3%, respectively. The AT content was higherthan the GC content. Twenty four haplotypes and43polymorphisms were inferredamong COI from three populations,9haplotypes and19polymorphisms were definedamong16S rRNA from three populations. The fixation indices (Fst) analyzed byAMOVA totaled to Fst=0.0.0090(P<0.001) and Fst=0.0674(P<0.001), showing thatthe genetic fixation intra-populations is larger than that of inter-populations, andindicating significant genetic fixation among the three populations. The Neighbor-joining phylogenetic tree was constructed from the three populations of P.amurensis. The result showed that the three populations might have originated from oneclade, while a small number of individuals mixed in other groups.5. The genetic diversity of three populations of P laevis based on mitochondrialCOI gene fragment. Universal primers were used for COI gene sequences amplificationof three geographic groups of P. laevis from DongYing, WeiFang, RiZhao, and30COIgene sequences in size of665bp were obtained. The nucleotide composition of A, T, C,G, and AT were respectively46.2%,13.3%,21.7%,18.8%and67.9%. AT content washigher than that of GC. Eighteen haplotypes,31nucleotide polymorphic loci of COIgene were detected in our study. The study reveals that the three groups of P. laevis havesmall genetic differentiation among them. From the phylogenetic trees constructed byNJ method and UPGMA method, we find that the three geographical groups of P. laevisconverge together and individuals of them blend together.The above results of potamocorbularub provide some basic data for breedingresearch and molecular genetic diversity study.