Discerning the Ecological History of a Cyptogenic Marine Snail, Littorina Littorea

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L. littorea is a conspicuous and ecologically dominant species in the intertidal community of New England, influencing the distribution and abundance of intertidal species through competition and heavy grazing. Despite its prominence, its biogeographic history remains unclear. L. littorea was first recorded in North America in 1840 in Pictou, Nova Scotia. Within 40 years of its establishment in the Gulf of Saint Lawrence, it had spread ~1500 km southwards to New York. For over 100 years scientists have debated whether the population that invaded the northeast United States was introduced from Europe or was native to Canada and expanded its range southwards. A characteristic often used to determine whether a species is nonindigenous is a reduction in its genetic diversity (founder effects) in the introduced population compared to the native range. By genetically sequencing snail populations on both sides of the Atlantic, the PIs will discern the ecological history of L. littorea in the northeastern United States. Additionally, L. littorea is infected with at least five trophically transmitted trematode parasites within North America. Thus, the PIs will employ a novel second approach by examining the potential reduction in the genetic diversity of the parasite species themselves in the introduced region. Since parasites typically infect only a fraction of hosts, the PIs expect founder effects to be more pronounced in parasites introduced with the hosts. This study uses a multifaceted approach to resolve L. littorea.s ecological history in the nearshore community of North America. New evidence will be generated on the biogeographic origin of L. littorea by assessing the genetic diversity of L. littorea and its trematode parasites. Intellectual Merit. Not only will this project inform the ecological history of a dominant marine species, but it will also develop a powerful general approach to inform the origin of many cryptogenic species. Analyses of genetic signals of both parasites and hosts may prove to be a powerful combination in unveiling the ecological history of invasive species. Broader Impacts. This project includes support of a graduate student and several undergraduates. This project will create mentored research opportunities for undergraduates in particular by involving a student at the Shoals Marine Laboratory REU program. Results of this project will be broadly disseminated in high impact journals, presentations at scientific meetings, and a publicly available website. If results of this work are favorable they will provide ample data to allow a strong resubmission of a full proposal to NSF to support related follow-up work in this system.