A High-density Genetic Map And Growth-related QTL Mapping In Gynogenetic Brown-Marbled Grouper(Epinephelus Fuscoguttatus)

The brown-marbled grouper（Epinephelus fuscoguttatus）is the femaleparent of hybrid grouper（E.fuscoguttatus×E.lanceolatus）（GS-02-004-2016）,which plays an important role in the germplasmresources of grouper.Gynogenesis and molecular marker-assisted selection（MAS）breeding is one of the most efficient breeding methods for fish with long reproductive cycle.In this study,the genetic improvement of brown-marbled grouper was carried out by integrating the techniques of artificial gynogenesis,MAS breeding and phenotype selection.Firstly,the relationship between morphological traits and body mass was analyzed based on the family of gynogenetic brown-marbled grouper.Then,SNPs were mined by GBS technology to construct a high-density genetic linkage map.Finally,quantitative trait locis（QTLs）related to growth were mapped.The results will lay a theoretical foundation for breeding of brown-marbled grouper,and also provide basic information for the large-scale breeding of hybrid grouper（E.fuscoguttatus×E.lanceolatus）.The research results of this study are as follows:（1）Correlation analysis between morphological traits and body mass of gynogenetic E.fuscoguttatus.The relationship between morphological characters and body mass of mapping family was analyzed by correlation analysis,path analysis and multiple regression analysis.The results showed that the pairwise correlation among the traits reached a very significant level（P<0.01）except eye diameter,and the maximum correlation coefficient between total length and body mass was 0.939.The multiple collinearity test shows that the whole length is seriously collinear,so it was excluded in subsequent analysis.Path analysis and coefficient of determination analysis showed that the four selected traits were the main traits affecting body weight（R²=87.2%）,and the direct effect of body length on body weight was the largest（path coefficient=0.447）.Multiple linear regression equations were established with body mass（BM）as dependent variable,body length（BL）,body height（BH）,caudal peduncle height（CPD）and head length（HL）as independent variables:BM=-490.247+44.139*HL+66.086*CPD+6.707*BL+12.182*BH was constructed by stepwise method.In conclusion,the selection of 11-month-old gynogenetic E.fuscoguttatus should be based on the body length as the main selection trait,and the body height,tail stalk height and head length as the auxiliary selection traits.（2）Construction of high-density genetic linkage map in gynogenetic E.fuscoguttatus.In this study,the 164 gynogenetic F₁offspring and female parents of E.fuscoguttatus were used as mapping population.Whole-genome resequencing and genotyping by Sequencing（GBS）were used to develop the single-nucleotide polymorphisms（SNPs）to female parent and F₁offspring,respectively.A high-density linkage map of gynogenetic brown-marbled grouper was constructed with 19301 SNPs located in 24 linkage groups（LGs）.The genetic length of the consensus map was 2343.72 c M,with an average genetic length is 97.655 c M and average marker interval of 0.12 c M.The results provide a reference for the construction of genetic map of single parent gynogenetic families and a framework for mapping of QTL.（3）QTL mapping for growth traits in gynogenetic E.fuscoguttatus.On the basis of phenotypic data evaluation and genetic linkage map,6 growth related traits were selected for QTL mapping.A total of 17 genome-wide significant correlation QTLs and 12 chromosome-wide QTL were detected in 5 LGs（LG3,LG5,LG8,LG11 and LG16）,which were related to growth trait.For QTL of growth-related traits,multiple loci were found to be shared on LG3,LG8 and LG16,and several important growth-related candidate genes were identified:raptor,pcyt2,exosc1,adcy3,eys and adgrb3.The functions of these growth-related candidate genes are mainly involved in the regulation of cell cycle,cell proliferation,energy metabolism and intracellular signal transduction.