Genetic characterization of the invasive zebra mussel (Dreissena polymorpha) in the Iberian Peninsula

The zebra mussel, Dreissena polymorpha (Pallas, 1771), is a successful invasive bivalve native to the brackish and freshwaters systems of the Ponto-Caspian regions. It is considered one of the world’s 100 worst invasive alien species and has high ecological and economic impacts. Over the past 200 years, it has expanded across the European and North American continents. Since the recent invasion of the Iberian Peninsula in 2001, D. polymorpha has expanded along the Ebro River basin and colonized adjacent basins in Northeastern Iberia. Using 9 microsatellite markers, we analyzed one population from the low Danube and several European and North American introduced locations, including a large number of Iberian sites, to genetically characterize the zebra mussel invasion and to identify putative routes of colonization. Our results reflect a high homogeneity of the Iberian samples, indicating that D. polymorpha colonized the Iberian Peninsula via a single invasion event. The genetic singularity of the populations observed in this region (including 9 unique alleles and significant genetic distances with the rest of analyzed samples) indicates that additional sites from the native and introduced range must be sampled to identify the source of the Iberian invasion.