Microsatellites are one of the most popular markers in genetic studies but typically they
need to be isolated and characterized de novo for each species. In this
work, a genomic library enriched for a trinucleotide motif was constructed to identify
polymorphic microsatellite loci in Aequipecten opercularis, a scallop
species commercially fished in Europe, and to examine the level of genetic variation and
genetic differentiation in samples from Spain and Northern Ireland. Sequencing of 83
clones led to the identification of 30 microsatellite-containing sequences which showed
often other repeated sequences. Five microsatellite loci were successfully amplified and
found polymorphic. The number of alleles and the expected heterozygosity per locus ranged
from 9 to 86 and 0.341 to 0.927, respectively, all localities showing similar levels of
genetic variation (allelic richness, 13.164–15.487; expected heterozygosity, 0.527–0.638).
Discrepancies in genotype proportions from Hardy-Weinberg equilibrium were observed in 11
out of 25 locality-locus combinations, a heterozygote deficiency occurring in all cases
probably due to null alleles. Significant genetic differentiation was detected among
A. opercularis from Northern Ireland, Fuengirola (southern Spain) and
the homogeneous samples from northwest Spain. Isolation by distance was the most likely
hypothesis to explain the differentiation detected.