Analysis On Dominance And Indirect Genetic Effects For The Selection Populations In Shrimp

In recent years,with the rapid expansion of the aquaculture farming,most aquatic species suffered from severe degeneration of germplasm,such as slow growth rate,decrease in disease resistance and high mortality,which severely restricting the healthy and sustainable development for the aquaculture industry.The selective breeding could provide high quality seed that has huge implications for the stable development of aquaculture.Accurate estimation on the genetic parameters for the quantitative traits is crucial to estimate breeding values,to design selection index,to predict response to selection and to optimize breeding scheme.However,most of selective breeding programs targeted only on additive genetic effect,ignoring the dominance genetic effect and indirect genetic effect(IGE).In this study,we investigated the dominance and indirect genetic effects on the body weight for the selection populations of Macrobrachium rosenbergii and Litopenaeus vannamei.We hope the results will provide theoretical basis for increasing the genetic gain of object traits in shrimp.The results are listed as follows:1.Estimation of additive and dominance genetic effects for harvest body weight in advanced generations of Macrobrachium rosenbergiiThe accurate estimation of additive and dominance genetic effects is fundamental to improving the accuracy of selective breeding and accelerating the speed of genetic gains.A total of 29523 individuals from 343 full-sib families(244 half-sib families)were harvested and measured in the G7,G8 and G9 generations of Macrobrachium rosenbergii.The variance components of harvest body weight for four datasets including G7,G8,G9 and G8+G9,were estimated using the average information restricted maximum likelihood method based on two single-trait animal models.The two models were described as follow: 1)the additive genetic model: additive genetic effect plus common environmental effect(A+C).2)the additive-dominance model: in addition to A and C,dominance genetic effect was also included in the model(A+D+C).For the A+C model,heritability estimates of harvest body weight for the four datasets were all low(h2?0.15)and ranged from 0.046±0.045 to 0.082±0.035.For the A+D+C model,the heritability estimates of harvest body weight ranged from 0.063±0.070 to 0.096±0.086 and the ratio of dominance genetic variance to phenotypic variance ranged from 0.027±0.015 to 0.571±0.063.Heritability estimates for harvest body weight decreased for the G7,G9 and G8+G9 datasets,except for the G8 dataset in which an increase was observed.Low heritability estimates for harvest body weight indicate that wild or improved populations with great production performance have to be introduced and integrated with the nucleus breeding population.In addition,large differences on the ratio of dominance genetic variance to phenotypic variance among different datasets suggest that the accuracy of dominance variance estimate should be improved by new algorithm with the datasets including more generations2.Genetic parameters and genotype by environment interaction for direct genetic effect(DGE)and IGE of body weight arising from two feeding strategies in Litopenaeus vannameiTo examine and compare the effect of social interaction among individuals on the estimation of genetic parameters for body weight,6720 shrimp from 80 tagged families were tested with ad libitum(AF)and restricted(RF)feeding strategies.Each family was separated into three groups(14 shrimp per group)that were randomly assigned to 80 net cages(70 cm × 70 cm × 100 cm)with shrimp from two other families in each feeding strategy.Variance components for body weight in each strategy and the genotype by environment interaction(G×E)between feeding strategies were estimated using an animal model excluding or including IGE.Heritability estimates of body weight from the conventional animal model for RF and AF strategies were 0.25±0.11 and 0.11±0.091,respectively.The log likelihood ratio test revealed significant IGE on body weight.The IGE variance expressed relative to total heritable variance was 692.18% for RF strategy and 66.78% for AF strategy,which indicated that a substantial heritable and available genetic variation was due to the social interaction among individuals.The direct-indirect genetic correlation for body weight in RF and AF strategy was-0.93±0.15 and 0.32±0.47,respectively.The strongly negative latter showed that the presence of strongly competitive heritable interactions among individuals when feeding was restricted.The highly estimated genetic correlation of DGE on body weight between feeding strategies was 0.94±0.07,and K<0.5(K=0.06),suggesting the G×E effect was not significant.The moderately estimated genetic correlation of IGE on body weight was 0.67±0.20,and K>0.5(K=0.70),suggesting the G×E effect was significant.3.Genetic parameters and genotype by environment interaction for direct and indirect genetic effects of body weight arising from two stocking densities in Litopenaeus vannameiTo examine and compare the effect of social interaction among individual on the estimation of genetic parameters for body weight,6210 shrimp from 90 tagged families were tested with high(HD,280 individuals/m2)and low(LD,150 individuals/m2)stocking densities.Each family was separated into three groups(HD: 15 shrimps per group;LD: 8 shrimps per group)that were randomly assigned to 90 net cages(40 cm × 40 cm × 100 cm)with shrimp from two other families in each density.Variance components for body weight in each density and the genotype by environment interaction(G×E)between densities were estimated using an animal model excluding or including IGE.Heritability estimates of body weight from the conventional animal model for HD and LD were 0.04±0.12 and 0.47±0.23,respectively.The log likelihood ratio test revealed significant IGE on body weight.The IGE variance expressed relative to total heritable variance was 298.50% for HD and 1871.85% for LD,which indicated that a substantial heritable and available genetic variation was due to the social interaction among individuals.The direct-indirect genetic correlations for body weight in HD and LD were-0.95±0.26 and-1.08±0.33,respectively,which indicated the presence of strongly competitive heritable interactions among individuals for the two stocking densities.The estimated genetic correlations of DGE or IGE on body weight between stocking densities were all higher than 0.9,suggesting that G×E effects were not significant.