Resolving the 150 year debate over the ecological history of the common periwinkle snail, Littorina littorea, in northeast North America.

摘要

Littorina littorea (common periwinkle snail) is highly abundant in both Europe and North America. A known native of Europe, its presence in North America has been the subject of a one-hundred year debate. Prior published work attempting to resolve its cryptogenic (=uncertain origin) status with historical, archaeological, ecological and/or genetic data were not successful. I therefore included novel parasite and molecular evidence to definitively resolve L. littorea's North American cryptogenic status.;First, I explored trematode species richness patterns in European versus North American L. littorea and two co-occurring native congeners, L. saxatilis and L. obtusata. Through extensive field and literature surveys, I found only L. littorea to possess significantly fewer trematode species in North America, while all Littorina sp. North American trematodes were a nested subset of Europe. Overall, these results suggest a recent invasion to North America for L. littorea and an older, natural expansion to North America for L. saxatilis and L. obtusata..;Second, I explored genetic founder effect signatures in North American L. littorea. I sequenced a ∼1200 base-pair region of mitochondrial DNA in nearly 400 Europe and North American snails. My results demonstrate a significant reduction in overall genetic diversity in North America versus Europe, nested and common haplotype frequencies in North America, and a divergence estimate of no greater than 450 years ago.;Third, I explored genetic founder effect signatures in L. littorea's most common trematode parasite, Cryptocotyle lingua. I sequenced a 1043 base-pair region of mitochondrial DNA and found Cr. lingua to show several signatures of a recent introduction to North America, including a significant reduction in haplotype diversity in North America, nested and common haplotype frequencies in North America, and a range of divergence estimates between 240-480 years ago.;Altogether, these three corroborative pieces of evidence suggest a recent, likely human-mediated introduction of North American L. littorea from Europe. This work represents the first time ecological studies of parasites and genetics have been used in concert to resolve the cryptogenic status of an important marine species. The successful application of these techniques can therefore be useful in cryptogenic investigations worldwide.