Allozymic variability in the Iceland scallop Chlamys islandica: geographic variation and lack of growth-heterozygosity correlations

Abstract

Populations of the Iceland scallop Chlamys islandca from the waters off Jan Mayen, Spitsbergen, Bear Island and northern Norway were inveshgated for allelic variation at 6 polymorphic gene loci. The 3 loci encoding for glucose phosphate isomerase (GPI), phosphoglucornutase (PGM) and superoxide dismutase (SOD) substantiated earlier findings of exceptionally high polyrnorphism at these loci in the Iceland scallop, higher than for many other pectinids. Loci encoding for malate dehydrogenase (MDH) and leucine-arninopeptidase (LAP) also exhibited higher polymorphism than is known for other pectinids. The high variability at an increasing number of enzyme coding loci for the subarctic/arctic species appears to contrast with predictions of negative correlations between environmental homogeneity and gene polymorphism. Allele frequencies at Mdh. Pgrn and Sod varied between populations over the geographical range surveyed, giving supportive evidence of at least partial geographic isolation between stocks. Data of the present study do not provide evidence that multiple-locus or single-locus heterozygosity affect longevity of C. islandica. Heterozygosity did not increase with age of the scallops, nor were positive growth-heterozygosity correlations demonstrated, either at singlelocus or multiple-locus heterozygosity. This contrasts with findings for several other bivalves, but is in accordance with observations for other pectinids.