A test for overdominance at the phosphoglucomutase-2 locus in Pacific oysters ( Crassostrea gigas) from New Zealand

Abstract

The biochemical basis of overdominance for specific activity at the phosphoglucomutase-2 (PGM-2) locus has been reported for Pacific oysters ( Crassostrea gigas) that are formed from heterozygous combinations of the allele at highest frequency and any other allele at this locus [Pogson, G.H., 1991. Expression of overdominance for specific activity at the phosphoglucomutase-2 locus in the Pacific oyster, Crassostrea gigas. Genetics 128, 133-141.]. It was suggested that this form of overdominance might explain soft tissue growth differences among adult wild Pacific oysters that are frequently reported in the literature. In the context of New Zealand's Pacific oyster aquaculture programme, we investigated the feasibility of using this overdominance as one of several different, but complementary, genetic approaches to achieve production gains for a hatchery-based breeding programme. There was no evidence of either a PGM-2 genotype-dependent effect or of overdominance for wet tissue weight among the wild juvenile oysters (9 months of age) or among the adults of this same batch of oysters 12 months later after they had been on grown. Among juveniles (5 months of age) from each of 8 full-sib hatchery reared families, there was no evidence of a PGM-2 genotype-dependent effect or of overdominance on dry shell weight, wet tissue weight, or total tissue weight within any of the families. When these juvenile oysters were pooled without regard to family, there was no evidence of overdominance for dry shell weight, wet tissue weight, or for total body weight (=dry shell weight plus wet tissue weight). Despite finding no evidence for an overdominant effect at the PGM-2 locus within either wild or hatchery-produced Pacific oysters from New Zealand, we suggest that further evaluation of the PGM-2 overdominance effect is warranted to determine if the overdominant growth advantage previously reported in the literature is present among adult oysters grown at aquaculture sites.