Date of Award


Degree Type


Degree Name

Master of Science




Biology (MS)

First Advisor/Chairperson

Kurt Galbreath


Parasites are an understudied group that can provide important information on ecosystem dynamics and climate change as well as host biogeographic history. I performed a comparative biogeographic study on two endoparasitic helminth lineages associated with pikas (Ochotona) -the tapeworm genus Schizorchis and the pinworm subgenus Labiostomum (Eugenuris). Colonization history across Beringia was assessed using analyses of historical range estimation and tests for simultaneous divergence. Analysis results allow me reject the hypothesis that these parasites colonized the Nearctic during a single glacial cycle, as evidenced by multiple Nearctic and Palearctic lineage pairs that did not diverge simultaneously. This evidence indicates a pre-Pleistocene (>2.5Mya) history of multiple, independent colonizations of pikas and their parasites across Beringia primarily in an eastward direction. Comparison of these two major parasite lineages indicates semi-independent histories, with trans-Beringian parasite lineage formation likely driven by taxon pulses, with expansion and vicariance cycles reflecting periods of environmental stability and perturbation, leading to complex histories of colonization and host-switching within pikas.

Access Type

Open Access