Parasites may be transmitted between native and invasive species during invasions; however, the importance of parasites for most invasions is unknown. In the Great Lakes region, a trematode parasite (Microphallus sp.) reduces invasive rusty crayfish (Faxonius rusticus) population growth and antipredator behavior. Microphallus also reduces antipredator behavior in native congeners (F. virilis and F. propinquus) to a greater extent than in F. rusticus. We were interested in whether this parasite was introduced to the Great Lakes region with F. rusticus, or if it was transmitted to F. rusticus from a native congener. Further, we were interested in whether Microphallus has greater behavioral effects on novel hosts or hosts with which it shares a long coevolutionary history. To answer these questions, we genotyped parasites to determine whether the same species of parasite was present in all three crayfish congeners and whether it was present in the native range of F. rusticus. We collected all three congeners from 25 lakes in the Great Lakes region and F. rusticus from 38 streams in the native range. We sequenced an ~800 bp region of the mitochondrial COI gene for 182 trematode parasites from collected crayfish.
Results/Conclusions
Parasite genotypes were similar among all three crayfish hosts in the Great Lakes region and diverged significantly between the Great Lakes region and native range of F. rusticus. These data suggest that the species of Microphallus present in the Great Lakes was transmitted from congeners to F. rusticus after it was introduced. Thus, Microphallus affects crayfish behavior to a greater extent in hosts with which it shares a long coevolutionary history. This parasite is trophically-transmitted, so reducing crayfish antipredator behavior may be an adaptation of the parasite to increase transmission to higher trophic levels. These results provide new evidence that the behavioral effects of trophically-transmitted parasites may be diminished in novel hosts and that parasites acquired by invasive species can alter their impacts.