Estimation Of The Heritability Of Important Economic Traits And Construction Of High Density Genetic Linkage Map For Sea Cucumber(Apostichopus Japonicus)

Currently, the sea cucumber（Apostichopus japonicus） has become one of the most important aquaculture species in China, achieving valuable profits. Over the last decades, sea cucumber aquaculture industry expands rapidly, but there is a slowly progress in genetic breeding of sea cucumber, and a varity of problems has limited the development of acquaculture industry, for example, low growth rate, high frequency of disease, fragile stress-resistant ability. Selective breeding and genetic analysis may provide theoretical guidance and materials for sea cucumber breeding practice, as well as high quality seed for sea cucumber aquaculture. In this study, heritability assessment, family estimation, high density genetic linkage map construction and QTL analysis were conducted, the main main results were listed as follows:1. Estimation of heritability for main economical traits of sea cucumberIn order to provide heritability reference for breeding practice, 23 full-sib families were constructed using the materies of our projiect selected. the heritability of body length, body weight and the number of pallet of 9-month-old sea cucumber were calculated according to the quantitative genetics theory,. The results showed that the heritability of body length in full-sibs, maternal half-sibs and paternal half-sibs were estimated to be 0.86, 0.87 and 0.85, respectively. The heritability of body weight in full-sibs, maternal half-sibs and paternal half-sibs were estimated to be 0.46, 0.20 and 0.73 respectively. The heritability of the number of pallet in full-sibs, maternal half-sibs and paternal half-sibs were estimated to be 0.37, 0.43 and 0.32, respectively. T test results showed that the heritability of body length and body weight in paternal half-sibs are significant（p<0.05）, and the heritability of body length and body weight in full-sibs are extremely significant（p<0.01）, but the heritability of the number of pallet in full-sibs, maternal half-sibs and paternal half-sibs were not significant. The estimation of heritability for the 3 economic traits of large-scale seeds could provide theoretical basis and technical reference for the following artificial breeding of A. japonicus.2. Comparison and analysis of stress resistance and growth performance between different familiesIn order to evaluate and screen out the family with high growth rate and strong stress-resistant ability, the 23 family we constructed were carried out with high temperature tolerance, low salinity tolerance and bacterial infection trial respectively（experimental group and control group were repeated 1 time with same method） and measurement of body length and body weight. The results showed that the distribution range of the body is（3.47±0.15）^6.24±0.28cm, the family D2 has the largest average body weight in 9-month-old,the average body weight is（12.10±1.17）g, which is 6.2 times of the B4 family,the 5 families which have the good performance in body weight are D2,E5,C1,E2 and C3; After the trail of temperature tolerance,the survival rate of E2 family was highest, the survival rate is（46.67±3.33）%, the survival rate of A5 family is 0, the average survival rate is（19.71±1.98）%, the 2 families which have the good performance in high temperature resistance are E2 and B4; After the trial of salinity13 tolerance, the survival rate range from（23.33±3.33）% to（63.33±6.67）%, the survival rate of A4 and A5 are higher than 60%, the survival rate is（63.33±6.67）% and（63.33±0.00）% respectively, After the trial of salinity 14 tolerance, the survival rate range from（55.00±1.67）% to（81.67±1.67）%, the survival rate of D5 and D1 are higher than 80%; After the trial of bacterial infection, the survival rate of different families range from（6.67±1.67）% to（81.67±1.67）%; Finally we selected 7 families（A3, B5, C1,D1, D2, D4, D5） as the family with strong stress-resistant ability and high growth rate through clustering analysis and multiple comparision.3. Construction of high-density genetic linkage map and QTL mapping for main economical traits in sea cucumberThe construction of genetic linkage map and QTL mapping for economical traits were carried on F1 populations（142 individuals and 2 parents） using the SLAF-seq technology and High Map software. Finally we obtained 264810 SLAF markers among these markers, there were 112322 polymorphic SLAF markers. The linkage map we constructed contains 23 linkage groups, mapped marker amount to 3223.84 c M for integrated map, 3864.73 c M for male map and 2075.84 c M for female map. The average distance between 2 mapped markers is 0.92 c M, 1.92 c M and 1.10 c M for integrated map, male map and female map. Quantative traits loci associated with body length, body breath, body weight, papilla number and disease resistance were identified by the method of Internal Mapping through the software of High Map, Finally 9 QTL locus were detected which associated with the 5 economical traits through QTL analysize, There were 1 QTL locus in 22 linkage group associated with body length, which contained 1 SNP markers and could explain 14.3% of the phenotypic variation; There were 2 QTL locus in 22 linkage group associated with body breadth, which contained 8 SNP markers and could explain 9.7¹1.2% of the phenotypic variation; There were 2 QTL locus in 22 linkage group associated with body weight, which contained 12 SNP markers and could explain 11.1¹1.8% of the phenotypic variation; There were total 5 locus in 7 and 12 linkage group associated with the number of papilla,which contained 5 SNP markers and could explain 11.1¹1.8% of the phenotypic variation; There were total 2 locus in 8 and 19 linkage group associated with the disease resistance,which contained 55 SNP markers and could explain 9.3⁷4.6% of the phenotypic variation.