Terrestrial communities in North America were assembled through a history of climate-driven colonization across the Bering Land Bridge, which periodically connected Asia to North America during the Pleistocene. Taxa moving across the bridge carried their parasites, and studying these parasites can inform our understanding of the host’s intercontinental dispersal. For instance, the pika, a small lagomorph, carries a wide diversity of parasites that have recently indicated two different aspects of pika biogeographic history. Phylogenetic studies of Schizorchis, a genus of tapeworms that resides in pikas, demonstrated two episodes of North American colonization from Asia roughly 10 million and 4 million years ago. Separately, evidence from five lineages of pika parasites depicted a northward colonization from North America’s Intermountain West to Northern Canada and Alaska. We tested these hypotheses using an extended dataset obtained from two subgenera of pinworms, Labiostomum (Labiostomum) and Labiostomum (Eugenuris). We sequenced three regions of DNA: two mitochondrial and one nuclear. We used these data to create phylogenetic trees that show the relationships between pinworms of different localities, which then depict the colonization history. Our results confirmed two episodes of eastward colonization; however, the south-to-north hypothesis was not supported. These findings imply distinct waves of eastward colonization by pikas, but movement of host populations within North America was not resolved.

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Kurt Galbreath

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