Heterosis and genetic diversity of intraspecific hybrids crosses between two selected lines of the Pacific oyster Crassostrea gigas

Abstract

For aquatic species, long-term intense artificial selection inevitably leads to decreased genetic diversity and increased genotypic purity in the population, which may lead to a reduction in the adaptation of populations to their environment. Consequently, how to restore a high level of population genetic diversity becomes a critical issue in the breeding process. In this study, a complete diallel crosses was performed utilizing “Haida No. 1”, which had been selected for 10 generations, and the Orange-shell line of the Pacific oyster (Crassostrea gigas), which had been selected for 8 generations. The growth and survival traits of the crossed and self-crossed groups were systematically evaluated during the larval and grow-out stages. Meanwhile, the population genetic diversity of the four combinations was also assessed using 18 microsatellite loci and mitochondrial cytochrome oxidase I sequences (mtCOI). The growth and survival of two reciprocal groups were significantly larger than those of two parental lines. Meanwhile, the average allelic richness (Ar), observed heterozygosity (Ho), expected heterozygosity (He) and number of alleles (Na) of the hybrids was considerably larger than two purebreds. Moreover, significant reduction in average inbreeding coefficient Fis was detected in hybrids when compared to purebreds. The results indicate that crossbreeding between selected lines could not only obtain phenotypically superior descendants, but also increase the genetic diversity of C. gigas.