Muddied Waters: Disentangling a Complex History of Range Expansion of the Northern Crayfish

The northern or virile crayfish, Orconectes virilis, is one of the most widespread crayfish species in North America, and continues to expand its range primarily through anthropogenic introduction into novel habitats. Although the historical distribution of O. virilis in the Prairie Provinces of Canada is largely unknown, a combination of surveys, fisheries reports, and recent collections suggests recent and rapid spread of the species in western Saskatchewan and Alberta. Current presence of O. virilis in multiple river systems of the Prairies suggests multiple colonization events, either through natural upstream dispersal from different drainages to the east, or through human-mediated translocation. Our objective was to determine potential routes of colonization into the region using multiple molecular markers. We studied regional and intra-river spatial patterns of genetic structure in O. virilis collected from the Prairie Provinces and adjacent states.  We found that O. virilis in the Canadian prairies is represented by two genetically distinct lineages. One lineage, restricted to southern Alberta, is genetically similar to O. virilis sensu stricto from the United States, and appears to have been introduced via illegal bait-bucket release.  The second lineage is widespread across the Prairie Provinces, North Dakota, South Dakota, and Minnesota, and displays regional patterns of genetic structure and diversity consistent with northward and westward expansion, as might be expected following glacial recession. Intra-river patterns in this latter lineage indicate contemporary expansion may be natural, albeit exceedingly rapid, raising questions of potential environmental factors associated with the spread. Our data also show hybridization in an area where individuals of both lineages co-occur, further complicating management issues.