Muscle esterase variation and size variation in the sand launce Ammodytes dubius

Esterase variation detected in homogenates of muscle tissue taken from the sand launce Ammodytes dubius in April, 1970 and 1971 is described. Eight alleles were found segregating at a single locus, and the frequencies of these alleles were homogenous in population samples taken on the Emerald Bank, off Nova Scotia, Canada, in successive years. When ordered by their electrophoretic mobility, the profile of the frequencies of these alleles was unimodal and symmetric. In both of the population samples, there were significant excesses of homozygotes and deficencies of heterozygotes. There was an association between genotype and size of individuals among homozygous genotypes; individual homozygous for the most common, intermediately-migrating allele were larger than homozygotes bearing alleles with relatively fast or slow mobilities.