Selective Breeding Effect And Microsatellite Analysis Of Breeding Line Of Razor Clam Sinonovacula Constricta

Sinonovacula constricta belongs to the Mollusca,Lamellibranchia,Heterodonta,Veneroida,Solenidae,Sinonovacula,one of the four aquaculture bivalve in China,the typical eurythermal and euryhalinous bivalve.With the development of bivalve breeding technology,the seedling of razor clam from the natural seedlings to the current artificial breeding mainly,and supplemented by the natural seedlings.Through many years of artificial razor clam culture,smallsize parent clam and improper inbreeding and other issues will lead to the genetic diversity of S.constricta decreased,causing the degradation of its germplasm resources.In recent years,the one year old razor clam is generally small,the cost of the two year old razor clam is too high,the breeding efficiency is low and the market of S.constricta breeding has not yet carried out for breeding selection.Therefore,the artificial breeding of S.constricta to improve the genetic traits,to cultivate a fast growth,good quality,strong resistance new varieties will be the main development direction of the sustainable razor clam culture.In order to improve the genetic traits of S.constricta,the new varieties with high growth rate and strong resistance were cultivated,and microsatellite molecular analysis was carried out for breeding offspring.Identification of breeding selection results from genetic stability and genetic availability,which aims to reveal the genetic variation of the breeding lines and provide the theoretical basis for its further breeding work.Breeding lines of Sinonovaculla constricta obtained in the research group through many year selection(selective intensity 2.063).The growth differences between breeding strain F5 and control population was compared.The selective reaction,realized heritability and heredity acquisition of F5 were evaluated.The results showed that there was no statistically significant difference in egg diameter and fertilization rate between F5(P﹥0.05)and the control group.However,the metamorphosis rate,survival rate and late shell length growth of F5 were significantly superior to those of the control group(P﹤0.05).The variation ranges of selective reaction of shell length,realized heritability and heredity acquisition of F5 in 7days to 360 days were 0.30-0.78,0.14-0.37 and 4.83%-42.18%,respectively,and 0.49±0.06,0.23±0.08 and(26.49± 11.73)%on average.This study suggests that continuous multiple-generation breeding of razor clam is effective.It can significantly improve its survival ability and major economic characters such as shell length and fresh body weight.The research demonstrates that continuous selection of razor clams for five generations is effective,and further breeding is feasible,in order to breed new varieties of razor clams which have desirable traits.The genetic gain of selected razor clams’ shell length is generally low,probably because of their own genetic nature and environmental impact.Razor clams belong to a mudflat bivalve hiding in caves of silt,and their long body will reduce their adaptability to the environment.Hence,in the following breeding work,we can focus on the weight selection of razor clams,in order to obtain more practical achievements.In the group breeding,the increase of the inbred line rate and the decrease of the number of effective parents may lead to the decline of the genetic diversity of the breeding population,which leads to the decline of the breeding group.In order to monitor the genetic differences in the selection process of the artificial breeding population of Sinonovacula constricta,the genetic diversity of the wild population of Sanmen,Yueqing breeding and the artificial breeding group of F6 was studied by microsatellite DNA marker.The breeding line F6 of shell length and body weight were significantly higher than that of Yueqing cultured and Sanmen wild populations,Indicating that the S.constricta for continuous multi-generation breeding has played a significant role,shell length and weight traits of the breeding line are fully improved.Microsatellite 10 loci showed high polymorphism in Yueqing population and Sanmen wild population,and showed low polymorphism in breeding group F6.The average allele number of the three groups ranged from 2 to 5,and the expected heterozygosity was 0.2130 ~ 0.8964 and 0.1000 ~ 0.8233,respectively.The average polymorphism information content(PIC)of them was 0.383122,0.50675 and 0.2773 in Yueqing population,Sanmen wild population and artificial breeding group.The results of the Hardy-Weinberg equilibrium(HWE)test showed that the 9 population-locus combinations in the 30 population-locus combinations significantly deviated from the HWE balance(P <0.05).Fst(F-statistics)range of 0.032 ~ 0.071,the genetic differentiation between the breeding line F6 of S.constricta and Yueqing breeding group was weak in differentiation level,genetic differentiation between the Yueqing population and Sanmen wild populations was in middle differentiation level,and genetic differentiation between the Sanmen wild populations and breeding line F6 was in middle differentiation level.The results showed that the genetic diversity of the constriction population of S.constricta was stable,but there was still a breeding space.The genetic diversity and target traits can be improved by increasing the number of parents and the hybridization of different strains of S.constricta.