HETEROZYGOTE DEFICIENCY AND POPULATION-STRUCTURE IN THE BIVALVE RUDITAPES-DECUSSATUS

The genetic structure of the bivalve Ruditapes decussatus from a Mediterranean lagoon was investigated at seven enzymatic loci. Samples of adults collected at the same period in different localities were genetically homogeneous. Slight allele frequency differences were observed between two annual cohorts of spat. Differences were observed between presumed cohorts of a large multicohort sample of adults. Heterozygote deficiencies were observed in multicohort samples of adults, but were not detected in cohorts of spat, nor in one sample of adults which presumably consisted of one single cohort. Thus, a relationship was found between genetic and demographic structures and is suggested to rely on the existence of differences arising through selection.