ABSTRACT
For a long time, European mountain ridges such as the Alps and Pyrenees formed dispersal barriers just like straits in marine waters (i.e., Irish Sea). However, zebra mussels attached to recreational boats transported on trailers bypassed the Alps and colonized one alpine lake after another in the 1970s and also colonized Italian water bodies southward; a process that is still going on (Kinzelbach 1992, Cianfanelli et al. 2010). Ireland was colonized by zebra mussels attached to recreational boats that were transported from the United Kingdom in seagoing vessels, hence bypassing the Irish Sea. All these barriers could be passed when delays in transport were substantially reduced as the European Union expanded and inner borders and abolition of the value added tax (VAT) on secondhand boats were removed (Pollux et al. 2003). Finally, mountains of the Pyrenees were passed, and dispersal of the zebra mussel on the Iberian Peninsula is still going on (Durán et al. 2010). The newly established populations appeared genetically most similar to nearby populations (Pollux et al. 2003, Astanei et al. 2005, Rajagopal et al. 2009).
