长牡蛎幼体生长性状的遗传力及其相关性分析

Estimates of heritabilities and genetic correlations for growth in Crassostrea gigas larvae

采用平衡巢式设计方法和人工授精技术,每个雄体配3个雌体,构建了12个半同胞家系和36个全同胞家系。应用数量遗传学的全同胞组内相关分析法,利用SPSS软件的GLM过程计算表型变量的原因方差组分,估算了长牡蛎幼体生长性状的遗传力。结果表明,5—25日龄幼体壳高狭义遗传力估计值为0.161—0.771,壳长狭义遗传力估计值为0.139—0.814,其中利用父系半同胞组内相关法估计壳高的遗传力依次为0.387、0.364、0.262、0.378、0.161,壳长的遗传力依次为0.383、0.398、0.302、0.361、0.139,二者均为中等遗传力。雌性亲本间半同胞个体具有较大的变异程度,存在着较大的母性效应;由雄性遗传方差组分估计的遗传力准确可靠,由父系半同胞组内相关法计算的狭义遗传力是长牡蛎幼体遗传力的无偏估计值。长牡蛎幼体不同生长时期壳高和壳长的遗传相关和表型相关均为正相关,相关系数的范围分别为0.091—0.820、0.224—0.360,表明以壳高或壳长为参数进行选育时,均可达到改良生长性状的效果。

Pacific oyster Crassostrea gigas is a widely cultivated aquatic species with an annual world production of 4.6 millions tons in 2006. C. gigas is cultured in most parts of Chinese coast including Liaoning and Shandong provinces in the north,and Fujian and Guangdong provinces in the south. Pacific oyster seeds are produced mainly by hatcheries. Although artificial seed production technology is well developed,genetic degradation,such as inbreeding depression, becomes a concern. To improve Pacific oyster industry, genetic improvement programs have been carried out in several countries. Selection, either natural or artificial, induces an inter-generational response only when the trait exhibits additive genetic variation. An index of additive genetic variation is narrow-sense heritability （h2） which is the ratio of additive genetic variance to phenotypic variance. According to the breeder＇ s equation, h2 is a key indicator when surveying the potential for genetic improvement in an unknown natural population with putative commercial value. Body size （and any of its surrogates suoh as mass, length and other linear dimensions） has been considered as one of the most important determinants of every possible aspect of an animal＇ s life history. In this study, the heritabilities of shell length and shell height of C. gigas larvae were estimated by means of intra group correlation of full-sib. Twelve half- sib families and thirty-six full-sib families of C. gigas were obtained by artificial fertilization of three females by single males based on a balanced nest design. The shell height and shell length of larvae were measured on day 5,10,15, 20 and 25 post-hatch （30 individuals per family）. Causal components of phenotypic variance were calculated with the GLM procedure of the SPSS software. The estimates of narrow-sense heritabilities were 0.161-0.771 for shell height and 0.139-0.814 for shell length. Narrow-sense heritabilities of paternal half-sib were 0.387,0.364,0.262,0.378 and 0.161 for shell height, and 0.383,0.398,0.302,0.361 and 0.139 for shell length at different stages, respectively. Analysis of variance showed that maternal effect existed because maternal genetic variance was significantly larger than paternal genetic variance. Hence, the estimates of narrow-sense heritabilities obtained from intra-group correlation of paternal half-sib were precise and unbiased for both shell length and shell height of C. gigas larvae at all stages. The medium heritability （0.1-0.4）at five different larval stages shows that it is possible to increase the shell size by selection during larval stage. The estimation of genetic and phenotypic correlation coefficients between the two growth traits at different stages were 0.091-0.820 and 0.224-0.360, respectively. Medium heritability estimates and positive genetic correlations indicate that both shell height and shell length should respond favorably to direct and indirect selection for growth. Further studies are needed to establish the precise contributions of these variation sources on adult stages in different environments to assess the real potential for the response to selection. [Journal of Fishery Sciences of China,2009,16 （5）： 736-743]