Substantial gene flow caused by long-term translocation between natural bank populations of the Peruvian scallop (Argopecten purpuratus) is supported by RAD-Seq analyses

The Peruvian scallop (Argopecten purpuratus, Lamarck 1989) is a marine bivalve of high commercial value in the aquaculture industry, with wild populations distributing from northern Peru to Chile. Growing demand for it in the world aquaculture markets and limited availability of hatchery-based seeds caused long-term seed translocations among wild populations to recover depleted local populations and for production needs. We investigated long-term translocation effects on the genetic diversity and structure of wild populations using next-generation RAD sequencing. We sampled individuals from Sechura, Lobos de Tierra, Samanco, and Bahia Independencia in Peru, and La Rinconada in Northern Chile. We identified 8,345 polymorphic RAD loci and 24,218 SNPs for the five populations. We estimated high observed heterozygosity for all populations and high SNP frequency compared to similar studies on marine bivalves. We detected no spatial divergence among populations in Peru (pairwise F_ST from 0 to 0.003), but strong differentiation with the population in Chile. Migration rate estimates suggested asymmetric directionality of seed translocation. Overall, our results support a remnant effect of an intense historic translocation and ongoing gene flow among wild populations in Peru, challenging the identification of outlier loci and certification of sustainable origin of cultured scallops using genetic markers.