Co-invasion or spillback: tracking the movements of the invasive faucet snail and its trematode parasites

Background/Question/Methods

Invasive species present one of the greatest threats to terrestrial and aquatic biodiversity. Understanding the source of an invasion and the mechanisms by which it is spread are vital to management efforts and basic research on invasion dynamics. However, this information often remains elusive and requires that the pathway of invasion be pieced together using historical observations rather than tracking it in real-time. Fortunately, natural history observations can now be coupled with genomic resources to better achieve this goal. We used these tools to recreate the invasion pathway of an aquatic freshwater snail (faucet snail, Bithynia tentaculata) from its native Europe to the Great Lakes and upper Mississippi River region of North America.

Results/Conclusions

We found genomic support for the hypothesis that the snail was first introduced to the Great Lakes and traveled in an east to west route, invading the Mississippi River, where it is currently progressing southward. The snail either co-invaded with several trematode species or has become an optimal alternative host to native trematodes (i.e., spillback). In either case, the trematodes have been implicated in large-scale waterfowl die-offs in the upper Mississippi River region. Waterfowl serve as the definitive host for these parasites. Similar die-offs are no longer observed in presumed established areas of the invaded range, despite the snail and trematodes still being present. Our goal now is to recreate the invasion histories of several of the trematodes to determine whether a co-invasion or spillback occurred, explaining the observed variation in virulence along this invasion pathway.