Evaluation Of The Effects In Hatchery Scapharca Broughtonii Release And Analysis Of Population Genetic Diversity

Scapharca broughtonii which is mainly distributed along the coast of east Asia, is an important marine bivalve with a high economic value in China. Recently, its natural resources have been declined significantly due to over-fishing and destruction of habitat environment. Aquaculture and releasing of S. broughtonii has been performed as one of many recovery efforts to solve the problem. However, no study reports the recapture rate of releasing and the impact of release on genetic variation of S. broughtonii. In this study, microsatellite markers were used to determine parentageation and evaluate its efficiency, and analyze recapture rate of released S. broughtonii. Meanwhile, we also compared the genetic variation between hatchery and wild population of S. broughtonii using microsatellite, and monitored the change of genetic diversity during different developmental stage. The information obtained in this study was useful for designing suitable management guidelines of cultured stocks and for the releasing and enhancement of the species in future. The results are as follows:1. Parentage determination and estimation of effective population size of S. broughtonii based on microsatellite analysisWith the rapid development of aquaculture industry, many problems, such as the loss of genetic variation and inbreeding rate among generations during breeding process have came into notice. It is of great importance to get the pedigree information. In this study, six highly polymorphic microsatellite markers (mean He=0.78 and PIC=0.75) were utilized to determine the pedigrees and the genetic variability between brood stock and offspring in a mass spawning event of ark shell, S. broughtonii. Parentage identification was performed on a total of 330 individuals, including 300 offspring and 30 candidate parents (16 females and 14 males). The results showed that the assignment rate was in accordance with simulation. Using 6 microsatellites reached a successful rate of over 99%. The allelic diversity of offspring populations and brood stock was similar with each other, but the expected heterozygosity of offspring was less than that of parents significantly (P<0.05). The observed heterozygosity of offspring was a little lower than that of parents, but not significant. All the 30 parents participated in the reproduction. And the existence of multiple paternity and maternity was detected in clutches and dams in these 30 parents. The variance of parental reproductive success and unequal sex ratio resulted in a decline in effective population size (Ne=26.08). An inbreeding rate of 7.68% of this small scale production indicates significantly inbreeding depression. Increasing the number of parents, balancing the sex ratio of parents and the contribution of gametes are effective measures to decrease the risk of inbreeding.2. The evaluation of the effects of S. broughtonii releaseIn this study,6 multiplex PCRs have been developed from previously isolated, microsatellites to increase the efficiency of genotyping. We used three multiplex PCRs to genotype the 46 parents which were used to produce releasing population and 208 recaptured individuals, obtained the genetic information of parents, and identified the releasing individuals by comparing the genotypes of the recaptured individuals and parents. Meanwhile, we compared the the genetic diversity of parents, offspring and released individuals identified from the recaptured samples, to monitor the genetic variation of S. broughtonii during the releasing procedure. The results showed that 66 of the 208 recaptured individuals were released offspring with a proportion of 31.73%. The genetic diversity of the released individuals in the later stage dropped significantly.3. Genetic variation between hatchery and wild populations of S. broughtonii in China based on microsatellitesIn this study, five hatchery populations of S. broughtonii were compared with two wild populations in China using 4 panels of multiplex PCRs. Results showed that the hatchery populations were slightly less variable than wild populations, but not significant. For the hatchery and wild populations, the average numbers of alleles per locus were 14.4 and 15.9, and the average expected heterozygosities were 0.817 and 0.835, respectively. Fst values showed significant genetic differentiation among the seven populations. The UPGMA clustering constructed on the basis of genetic distances between populations showed a clear separation of the hatchery populations and wild populations.