The genetic diversity pattern of Mytilus galloprovincialis in Galician Rías (NW Iberian estuaries)

Abstract

The culture of Mytilus galloprovincialis in Galician Rías (NW Iberian estuaries) is a milestone for the aquaculture development in Spain. Despite the significant advances made on several biological aspects of this species, no detailed phylogeographic studies have been carried out locally to determine how its genetic diversity is distributed among Rías where large intensive cultivation takes place. We report the largest study on genetic variation of Galician mussels using six microsatellites on 27 mussel samples from the main five Galician Rías. Despite the narrower geographical range comprised in this study, allelic richness and heterozygosity were 5% and 2.7% larger, respectively, in Galician Rías than in other samples from the Atlantic Iberian coast. This result suggests a relationship between allele diversity and the large population sizes of mussels cultivated in Galician Rías. The interpopulation differentiation ( F ST = 0.0122) was half of that previously reported for Iberian Atlantic samples ( F ST = 0.0240) using the same loci. This weak genetic divergence suggests that no genetic structuring exists neither within Rías (inner versus outer or northern versus southern banks) nor among the five Rías compared. The highest local differentiation was observed between the sample pools from Rías Altas versus Rías Bajas, which are separated by the oceanographic boundary described in Cape Finisterre. Current knowledge on seed management suggests that seed transfer between Rías has probably reduced the natural divergence that naturally exists between these pools. These results could be useful for the genetic management of Galician populations and may serve as a baseline in monitoring future genetic changes in their genetic diversity, either due to environmental impact or to management practices.