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

Abstract

Populations of the Iceland scallop Chlamys islandica from the waters offJan Mayen, Spitsbergen, Bear Island and northern Norway wereinvestigated for allelic variation at 6 polymorphic gene loci. The 3loci encoding for glucose phosphate isomerase (GPI), phosphoglucomutase(PGM) and superoxide dismutase (SOD) substantiated earlier findings ofexceptionally high polymorphism at these loci in the Iceland scallop,higher than for many other pectinids. Loci encoding for malatedehydrogenase (MDH) and leucine-aminopeptidase (LAP) also exhibitedhigher polymorphism than is known for other pectinids. The highVariability at an increasing number of enzyme coding loci for thesubarctic/arctic species appears to contrast with predictions ofnegative correlations between environmental homogeneity and genepolymorphism. Allele frequencies at Mdh, Pgm and Sod varied betweenpopulations over the geographical range surveyed, giving supportiveevidence of at least partial geographic isolation between stocks. Dataof the present study do not provide evidence that multiple-locus orsingle-locus heterozygosity affect longevity of C islandica.Heterozygosity did not increase with age of the scallops, nor werepositive growth-heterozygosity correlations demonstrated, either atsingle-locus or multiple-locus heterozygosity. This contrasts withfindings for several other bivalves, but is in accordance withobservations for other pectinids.