ABSTRACT: Electrophoretic examination of 8 allozyme loci in 10 Spanish natural populations of Crassostrea angulata revealed a high level of genetic variability in terms of average allele number, polymorphism and mean heterozygosity. Significant departures of genotypic frequencies from the Hardy-Weinberg conditions, which could not be explained after pooling alleles, were displayed at some loci. All populations showed a deficit of heterozygotes, according to Selander's D [(Het._observed - Het._expected)/Het._expected]; moreover, the mean D index across populations was negative for the Lap, Mdh-1, Mdh-2, Me-2 and Xdh genes, consistent with F_IT estimates, which indicates deviations from Hardy-Weinberg equilibrium within the total population. In contrast, loci Me-1 and Pgi were at equilibrium and Pgm showed a heterozygous excess. Null alleles appeared in Lap and Mdh-1 loci, which could have been responsible for the disequilibrium, at least in Mdh-1, because the increase of frequencies of null alleles was also related to the increase in the deficit of heterozygotes. Although a high level of gene flow between populations was detected, heterogeneity in the allelic frequencies of Lap, Mdh-1, Mdh-2, Me-2, Pgm and Xdh genes was shown to occur. Mean F_ST(F-statistic indicating deviations from Hardy-Weinberg equilibrium among populations) across loci was 0.031, meaning a slight genetic differentiation; however, no relationships were shown to exist between genetic distances, geographic distances and their location (estuarine or marine sites).

KEY WORDS: Crassostrea angulata · Polymorphism · Oysters · Genetic differentiation · Allozymes

Published in MEPS Vol. 154 (1997) on July 31
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1997