PCR-based nuclear markers identify alien blue mussel (Mytilusspp.) genotypes on the west coast of Canada

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Abstract
Two blue mussel sibling species, Mytilus edulis and Mytilus galloprovincialis, have been imported to Pacific northwest waters in separate attempts to circumvent early mortality experienced by the native species (Mytilus trossulus) when cultured. Here we describe two novel markers based on the polymerase chain reaction that discriminate the two non-native, or alien, mussel species from the native species. The two markers are inherited in a Mendelian fashion, show no evidence of close linkage, and are highly diagnostic. To screen British Columbian mussel populations for the presence of the alien species, we assayed genotypes at the two marker loci in 482 subtidal mussels collected at 12 sites. Animals with at least one alien allele were present at 9 of 12 sampling sites with an overall frequency of 6.2%. The distribution of alien alleles at the two marker loci differed among sampling sites, suggesting differential introgression. The widespread incidence of alien alleles, combined with evidence of extensive hybridization between the alien and native species, indicates that the introduced alleles will probably persist in British Columbia mussels for some time.