Genetic Parameter Estimation For Growth And Meat Rate Traits Of Pacific White Shrimp (Litopenaeus Vannamei) In Low Temperature Condition By Microsatellite Markers

The Litopenaeus vannamei,it is also called Pacific white shrimp and distributes in the Pacific coastal waters of the South America,it is one of important aquaculture species for shrimp in the world.The L.vannamei has the characteristic of wide adaptability,strong resistance to adverse environmental and fast growth.Moreover its meat is delicious and loved by people,therefore it has a very broad market prospect.However,due to climate anomalies in recent years,the cold disaster results the huge loss for L.vannamei's industry in L.vannamei's main farming areas of China's southern.The abnormal temperature not only causes large number of death for L.vannamei,but also restricts breeding season and area of L.vannamei,and then influences aquaculture production and efficiency.Therefore,for accelerating breeding new variety which have a good resistance to low temperature,it is urgent to estimate genetic parameters of resistant traits for L.vannamei.However.for the conventional breeding method called BLUP,the evaluation of genetic relationship between individuals is determined by the accuracy of manual record of the Pedigree,which can be influenced by mark off,misread,and common environmental effect,and futher make it hard to resulted to estimate genetic parameter accurately.In this study,genetic parameter estimation was by way of microsatellite markers,and construction of the Molecular Genealogy was determined by calculating the molecular genetic relatedness.Then we demonstrated the feasibility of molecular genetic relatedness in the actual estimation of genetic parameters by using cross validation.The main results were as follows:(1)In the present study,microsatellite loci with high polymorphism from the previously reported studies were selected to establish multiplex PCR systems and four multiplex PCR systems were successfully established by optimizing the combination,condition and procedure.We used the four multiplex PCR systems to perform pedigree analysis in 11 families of selected L.vannamei.The results showed that the average number of alleles(Na)were 6,the average of polymorphism information content(PIC)were 0.5813,and the average of observed heterozygosity(Ho)and expected heterozygosity(He)was 0.513 and 0.636,respectively.The four multiplex PCR systems were also used to verify their capacity of parentage assignment with Cervus 3.0 software in the 11 families of L.vannamei that the pedigree relationship was known.As a result,the combined exclusion probability of the first parent(CE-1P),the second parent(CE-2P),and a parent pair(CE-PP)were 0.99525487,0.99990862,0.99999986,respectively.Further analysis showed that,if all the multiplex PCR systems were used for pedigree analysis,both simulated assignment rate and parentage identification accuracy rate reached 100%,the full-sib and half-sib families had great identification,it showed that four multiplex PCR systems had good ability to identify.(2)In this research,four groups established multiplex PCR systems of L.vannamei were used to genotype for pedigree.We calculated molecular genetic relatedness by TrioML of Coancestry 1.0.1.2 software,constructed the Molecular Genealogy and then estimated genetic parameter for growth and meat rate traits of L.vannamei in low temperature condition by the Pedigree and the Molecular Genealogy,respectively.The results showed that molecular genetic relatedness of individuals was between 0 and 1,the mean was 0.058.The Pearson correlation coefficient of physics genetic relatedness and molecular genetic relatedness was 0.574,it was moderate positive correlation and showed the Molecular Genealogy constructed by molecular genetic relatedness had a higher credibility.Heritability estimation for body weight(BW),body length(BL),meat weight(MW)and meat rate(MR)by the Pedigree were(0.16±0.05?0.12±0.04?0.20±0.05 and 0.18±0.05,respectively.Heritability estimation by the Molecular Genealogy were 0.07±0.03(BW),0.04±0.02(BL),0.10±0.03(MW)and 0.10±0.03(MR),respectively.They were both low heritability.By the Pedigree,we calculated genetic correlation between meat rate and body measurements of L.vannamei,the results showed genetic correlation between meat rate and abdominal segment length(ASL)was the maximum(0.636±0.133),and average meat rate of L.vannamei's population in low temperature condition was 51.37%.The result of cross validation showed breeding value's the Pearson correlation coefficient of forecast and observed values between the Pedigree and the Molecular Genealogy were 0.56 and 0.55,they were close,and it indicated the Molecular Genealogy constructed by molecular genetic relatedness had similar accuracy than the Pedigree for breeding value estimation.Overall,microsatellite markers in genetic parameter estimation for aquatic animals have a huge potential.In this study,the obtained data can provide a reference for scientific breeding program,and it has a positive significance for resistance low temperature breeding of L.vannamei.