The Genetic Marker Screening For Growth And Reproduction Properties In Litopenaeus Vannamei

Litopenaeus vannamei, also known as South Amercia vannamei, natively lived in the Central and South America along the Pacific coast. It has a series of advantages such as fast-growing, strong anti-disease, nutritious, delicious meat and so on. Therefore it is widely intensive farmed in domestic and abroad. But in recent years, a lot of reasons such as the virus disease epidemic, water quality deteriorating, the farmers’ feeding and breeding in a wrong way and so on lead to the recession of germplasm. In order to rationally protect and make full use of the excellent germplasm that can expressed stably in progeny, this research is aimed at finding the effects of morphometric traits on body weight in different groups of Litopenaeus vannamei and selecting the genetic marker about growth and reproduction in Litopenaeus vannamei. From two aspects of quantitative genetics and molecular biology, we hope to provide some reference for Litopenaeus vannamei in genetic improvement.In quantitative genetics, One-way ANOVA, path analysis, and multiple regression analysis were applied to analyze 24 morphometric traits including carapace length(L1), length of the first to sixth abdominal segment(L2-L7), telson length(L8), body length(L9), total length(L10), carapace width(W1), the width of the first to sixth abdominal segment(W2-W7), carapace height(H1), the height of the first to sixth abdominal segment(H2-H7) in order to distinguish the morphological variation in 4 groups, V101, OS, NS, and GD2, of Litopenaeus vannamei and to find the main morphometric traits significant affecting body weight(m). The results showed that there were significantly morphological variation in the morphometric traits in the 4 different groups(P<0.05), with slender type in V101 and GD2 and high fat type in OS and NS. The correlation analysis, path analysis and degree of determination analysis revealed that other groups of morphometric traits are significantly(P<0.05)or very significantly(P<0.01) correlated with body weight except telson length of NS. Carapace length and carapace height had positive effects on body weight and that the second pleopod height had a negative effect on body weight in V101. In OS, the body length, the second pleopod length and carapace width were found to be positive and the sixth pleopod length negative. For NS, carapace length and the sixth pleopod height were positive, but carapace width was negative. For GD2, carapace length and total length were positive, but body length was negative.The 4 regression equations between body weight and morphometric traits were expressed as at very significant level(P<0.01) and all the multiple correlation indexes were greater than 0.85, indicating that the major morphometric traits affecting body weight were found. The findings indicate that the major morphometric traits affecting body weight were different in the 4 groups, and that morphometric traits for selection should be considered at different populations.In molecular biology, this research is to select the particular genetic markers of Litopenaeus vannamei about growth and reproduction in genome and transcriptome level. By comparing the different genotype quantitative characters’ mean and making sure whether there is a significant difference, we can find some genetic markers which have some linkage relationship with quantitative traits, which will greatly accelerate the process of genetic breeding.In terms of growth marker screening, we used the GD1 population in Saipan as the template. The 92 individuals’ DNA were amplified by using the good polymorphic 8 microsatellite primers which were selected by our lab members. In GD1 population, we found that 8 microsatellite primers were available because of its stable and clear banding pattern and showing different genetic polymorphism in different individuals. The results, which revealed the size of Amplified fragments between 126 bp and 258 bp, the number of effective alleles beween 1.28 and 2.53, observed and expected heterozygosis’ levels ranged from 0.25 to 0.64 and from 0.22 to 0.61. The loci polymorphism information showed that most of locus were in moderate and high polymorphism because of 3 locus(PIC) > 0.5, indicating high polymorphism, 0.25 < 3 loci(PIC) < 0.5, indicating moderate polymorphism, only two locus(PIC) < 0.25, indicating low polymorphism, which would lay the foundation for the next study of selecting the growth related genetic markers of Litopenaeus vannamei. The correlation analysis revealed that there were very significant effect of the TUM-6.124 for body weight(P<0.01),and other markers were not significant(P>0.5).We also found the dominant AA genotype which represented heavier individuals. In V101 and NS population, We found the same result that TUM-6.124 was very significant(P<0.01) and the dominant genotype is AA.In breeding marker screening, we choose the OS population in saipan as the template, among which, 25 spawning very good, 25 spawning just so so, 25 no spawning. 72 EST-SSR markers derived from Litopenaeus vannamei were selected and evaluated. Stable banding pattern were shown by 42 EST-SSR markers, and 12 of them were identified as the polymorphism EST-SSR markers, and can be used in the next study.In order to eliminate the influence of body weight, the breeding index was set to unit body weight spawning. 12 EST-SSR markers Associated with breeding index were Divided into two steps. The first step was to find some markers whether it can distinguish spawning or not. The result showed that marker V-3 was extremely significant difference(P < 0.01). There were 3 genotypes including AB, BB and BC in marker V-3. The ratio between the spawning and the no spawning in different genotypes(AA, AB, BC) is 20 to 1,15 to 11, 15 to 13.We inferred that AA genotype may have some relationship with spawning. The next step was to find some markers which can distinguish spawning well or not. The results showed that marker V-15 was extremely significant difference(P < 0.01) and other markers was not significant difference(P>0.05). The results of Duncan multiple comparison showed that genotypes of BB and DD is better than CD and BC. We also get the same result in GD2 population with V-15.In conclusion, the study set the foundation for population genetics studies, selective breeding, growth and breeding quality improvement in Litopenaeus vannamei.