An Investigation of Invasive Ecology and Genetics in Northern Indiana

Lumbricus terrestris, the common nightcrawler, is non-native in the Great Lakes region including northern Indiana, introduced from Europe after the last glaciation. Since its introduction L. terrestris has become established and widespread throughout the region, though there are identified areas where invasion has not yet occurred. Spread of this species is known to be related to human-mediated dispersal along roadways and at common fishing sites, where bait dumping occurs. The goal of this study was to determine whether landscape features such as the Eel River in northern Indiana facilitate the spread of L. terrestris populations. We hypothesized that the river connects L. terrestris populations, predicting that populations along the river would lack genetic differentiation, and retain higher genetic diversity, than populations in more isolated forest patches. We used six microstatelite loci to compare the genetic diversity of four earthworm populations along the river to two earthworm populations is forest patches. We found that genetic differentiation did not follow the predicted pattern, and that genetic diversity was high and widely varying among sample sites. A STRUCTURE analysis revealed only two genetic clusters, though tests of population differentiation revealed significant differences among several populations. Earthworm densities also varied greatly among sites, suggesting that further fine-scale and ecological studies are warranted in order to determine how landscape features affect earthworm invasion.