Population Genetic Diversity And Parentage Analysis Of Blunt Snout Bream (Megalobrama Amblycephala)

The blunt snout bream (Megalobrama amblycephala) is one of the commercially important species of fresh water fishes in Chinese aquaculture. To provide genetic background on germplasm of blunt snout bream(Megalobrama amblycephala), SRAP (sequence related amplified polymorphism) markers were used to investigate genetic diversity and genetic variation of natural populations from Liangzi Lake, Poyang Lake and Yuni Lake, breeding population of "Pujiang No.1" and cultured population from Yueyang, and to evaluate the novel molecular marker SRAP for its feasibility in parentage analysis of blunt snout bream from Liangzi Lake. The results obtained are as follows:1. Thirteen pairs of primer combinations, which were screened from 88 primer pairs, produced clear and polymorphic bands and were used for SRAP amplification. The numbers of amplified loci per primer pair ranged from 8 to 21, and a total of 172 loci were detected in three natural populations, a breeding population and a cultured population, of which 132 loci were polymorphism. Nei’s gene diversity (h) and Shannon’s information index (Ⅰ) ranged from 0.0904 to 0.1849 and 0.1371 to 0.2799 respectively. In the descending order the genetic diversity of 5 populations was Poyang Lake, Liangzi Lake, Yueyang, "Pujiang No.1" and Yuni Lake population.2. The genetic distance between the Yueyang and the Yuni population was the biggest (0.2701), and the genetic identity between the two populations was the smallest (0.7633). There was the smallest genetic distance (0.0866) between the Poyang and the Liangzi population with the biggest genetic identity (0.1970). The cluster analysis was carried out based on UPGMA method and revealed that five populations of blunt snout bream were pooled into three groups:Poyang Lake and Liangzi Lake, Yueyang and "Pujiang No.1", and Yuni Lake formed a single cluster.3. The AMOVA analysis indicated that the majority of genetic diversity was among populations,55.49% of the total genetic variation was among populations, and the differentiation occurred within populations was 44.51%. From the pairwise comparion of FST value, a high genetic differentiation was found among the five populations. Genetic differentiation between natural populations and breeding population or clutrued populations was obvious and the high FST value ranged from 0.52606 to 0.68538.4. Out of the total 240 primer combinations, only 10 appropriate primer pairs which displayed significant polymorphisms among eight families of blunt snout bream were used. A total of 105 fragments were identified in the study, of which 72 fragments (68.57%) were polymorphic. Among the eight families of blunt snout bream, the average Nei’s gene diversity (h) value ranged from 0.0514 to 0.1185. The average value of Shannon’s information index (Ⅰ) varied from 0.0747 to 0.1705. In addition, both of the Nei’s gene diversity and Shannon’s information index indicated that the level of genetic diversity of L36 was the highest, while L9 presented the lowest genetic diversity. The coefficient of differentiation (GST) among populations based on POPGENE was 0.6547, the gene flow was 0.2637. AMOVA analysis indicated that 67.25% of the total genetic diversity was among populations (FST=0.67248, P<0.001).5. The relationships between the offspring and their parents of eight families were investigated by the UPGMA cluster analysis based on Dice similarity coefficient. The results showed that individuals from the same family could cluster together. We selected 0.886 as standard measure value for classification, and these individuals were divided into six major groups. The three families of L30, L32 and L37 had the same male parent 2 in common, but L32 and L37 families showed less genetic similarity to their male parent. Except for individuals of L36 family, other seven families were clearly sought out their respectively parents. By the comparison of the genetic similarity between F1 individuals of L36 family and their suspected male parents, and their suspected female parents, it was showed that the mean similarity coefficient was the biggest between all the individuals from F1 of L36 family and their real male parent 5 (0.8076), female parent 10 (0.9066) respectively. The principal coordinate analysis (PCA), which was based on the genetic similarity matrix, showed similar grouping as the UPGMA dendrogram, and easily visualize the differences among all the individuals.