A team of biologists led in part by the University of Iowa has traced the origins of an invasive snail in the Great Lakes.

In a new study, published in the journal Molecular Ecology, the biologists say freshwater snails arrived in the Great Lakes from their native New Zealand and via Europe after being transported likely through ballast water to the continent in the 19^th century. The two lineages since have taken hold in the Great Lakes, altering ecosystems by covering rocks and vegetative surfaces and changing nutrient flow patterns. What remains to be seen is whether, like the infamous invasive zebra mussels, they crowd out native species, the biologists say.

“In this study, we retraced the pathway how these invasive snails got to the Great Lakes,” says Carina Donne, a second-year master’s student in the UI Department of Biology and first author on the study. “Once we know that, we can find out modes of transportation how they got there, and that information can be used to prevent future invasions.”

The snails first arrived in the western United States in at least 1987; in some lakes and streams in the region, they number as high 50,000 snails per square meter. They are believed to have been in the Great Lakes since about 1991.

The snails have been extensively studied in laboratories because females can reproduce sexually and asexually (without males). Each type—sexual and asexual—has been found in the Great Lakes.

Maurine Neiman, a co-author on the study and Donne’s mentor, says biologists seek to understand how asexual females are able to thrive as an invasive species, despite their low genetic diversity.

In general, she says, the snails have an advantage because “they’re really hardy, and they can withstand a lot of different types of environments. Native snails in New Zealand have a lot of parasites, worms that attack them. There are no similar parasites in the US, which might help explain why these snails are so invasive.”