Temporal patterns in allele frequencies of the gamete-recognition locus M7 lysin within a population of Mytilus galloprovincialis in southwestern England

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Abstract

Loci that encode proteins involved in gamete recognition often show patterns of rapid adaptive evolution and recent studies have shown that different alleles at gamete-recognition loci can be favoured under different sperm concentrations, leading to density-dependent selection during fertilization. While these density-dependent fertilization processes are likely to vary across time and space, it is possible that they are not typically observed at the larger scale of larval recruitment since most larval cohorts likely consist of multiple pools of larvae produced under a variety of sperm concentrations, which tends to homogenize the allele frequencies across time and space. We tested the hypothesis that allele frequency of the gamete-recognition locus M7 lysin in Mytilus galloprovincialis would show significant temporal variation among cohorts of spat and adult age classes. Adult and juvenile mussels and multiple cohorts of newly settled spat were collected from four locations within a predominantly pure population of M. galloprovincialis in southwestern England. Each mussel was then genotyped at the species-specific locus Glu-5′ and the gamete-recognition locus M7 lysin. Allele frequencies at Glu-5′ did not differ among any age classes or cohorts, suggesting that the samples did not contain migrants from adjacent hybrid populations with M. edulis. Similarly, there was little evidence of variation in allele frequencies at M7 lysin among cohorts of spat or among juvenile and adult age classes. The lack of significant temporal variation in allele frequency at M7 lysin suggests that the results of local and small-scale density-dependent selection may not typically be observed during recruitment of marine organisms with pelagic larval stages.

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