GPI GENOTYPIC EFFECT ON QUANTITATIVE TRAITS IN THE NORTHERN BAY SCALLOP, ARGOPECTEN IRRADIANS IRRADIANS

The relationships between glucose-6-phosphate isomerase (Gpi) genotype and quantitative variation related to reproduction and growth were ex plored over the lifespan of a single cohort of northern bay scallops, Argopecten irradians irradians (Lamarck), from September 1986 to April 1988 in the Niantic River estuary, Connecticut, USA. Analyses reveale d that Gpi genotype explained an increasingly significant proportion o f variation in scallop size (up to 15%) as the cohort aged. The genoty pe-specific effects were consistent across sampling dates and among me asured traits. There was no evidence for heterosis with respect to siz e at this locus; however, rare genotypes contributed substantially to the relationship and showed some tendency to fall on the extremes of t he phenotypic distribution. The strength and consistency of the genoty pic effect on scallop size suggest that genetic variation for Gpi, or some locus in linkage disequilibrium with Gpi, may translate into bioc hemical and/or physiological variation and affect fitness in this spec ies.