Multiple dispersal strategies of the invasive quagga mussel (Dreissena bugensis) as revealed by microsatellite analysis

The recent invasion of the Laurentian Great Lakes by Dreissena polymorpha and Dreissena bugensis presents a unique opportunity to study the role of high dispersal ability in the colonization success of invading species. While the dispersal of D. polymorpha has been characterized by several jump dispersal events, census data suggest a more gradual diffusion of D. bugensis from its point of introduction through the lower Great Lakes. In this study, we use six highly polymorphic microsatellite markers to investigate the present-day population genetic structure of D. bugensis in North America in an effort to clarify the role of multiple dispersal strategies in its colonization success. In contrast with survey data, which would suggest a gradual spread ultimately resulting in a pattern fitting a model of isolation-by-distance, the significant allelic and F-ST differences observed between 18 of 28 population pairs do not correlate with any simple geographic relationship. Deviations from isolation-by-distance are due, in part, to a higher gene flow between disjunct populations than that expected under a normally distributed pattern of dispersal. These results, in combination with recent reports of the quagga mussel outside its established North American range, suggest that boater-mediated jump dispersal of D. bugensis may be contributing to its colonization and spread in North America.