Microsatellite loci indicate population structure and selection between Atlantic and Gulf of Mexico populations of the bay scallop Argopecten irradians

Declines in populations of bay scallops over the last 3 decades have spurred interest in their conservation and restoration. The development of sound restoration and management strategies requires a clear understanding of the genetic diversity and structure of populations throughout the species' range. In an effort to assess the population genetic structure of bay scallops, we evaluated 6 populations in the western North Atlantic and the Gulf of Mexico using 9 microsatellite markers, 5 of which are presented here for the first time. Results of traditional F-statistics indicate strong population structure between scallops in the Gulf of Mexico and western North Atlantic (F-ST >= 0.120) and a low level of differentiation between North Atlantic (New York and North Carolina, USA) populations (F-ST = 0.035). However, distinct differences in high-frequency alleles at a single locus were largely responsible for the dramatic population genetic structure observed between Gulf and Atlantic populations. Further evaluation of loci by comparing observed data with simulated neutral distributions of FST indicates that selection is likely acting on the variation at 3 loci, while the variation at the other 6 loci does not deviate from the expectations of neutrality. Results suggest that the genetic structure between populations of bay scallops in the Gulf and Atlantic is affected by both selective pressure and restricted gene flow and that caution should be taken to maintain the native genetic diversity during commercial or restoration-based aquacultural activities.