Date of Award


Degree Type


Degree Name

Master of Science




Biology (MS)

First Advisor/Chairperson

Dr. Kurt Galbreath


During the Pleistocene, advancing glacial ice fragmented populations of species, which restricted populations from expanding, ultimately inhibiting gene flow. As glaciers receded, expansion out of unglaciated-isolated areas was possible. In addition to glacial barriers, landscape features such as rivers and mountain ranges served as barriers to dispersal of populations during the Pleistocene, influencing the phylogeography of multiple species. Though divergence between multiple lineages is a common feature of North American mammal diversity, circumstances that affected the post-glacial expansion of structured diversity within regions are less well-documented. Northern short-tailed shrews (Blarina brevicauda) are restricted to eastern North America, yet they exhibit three different mitochondrial lineages that diverged when historical populations retracted and became isolated from one another. In this study, I investigated the history of post-glacial expansion in historically isolated phylogroups of B. brevicauda, and interactions between these phylogroups across the contact zones where they meet. Using a genetic and morphological approach, I evaluated evidence for hybridization between historically isolated phylogroups of B. brevicauda by quantifying the distribution of genetic and morphological variation within and across contact zones. Individuals representing the Western phylogroup are larger than those of other lineages. In the Upper Peninsula of Michigan, where geographic overlap between adjacent B. brevicauda lineages is extensive, individuals that represent the Western genetic lineage are morphologically more similar to East-Central lineage individuals, indicating that genetic introgression between lineages is probable.

Access Type

Open Access

Available for download on Wednesday, April 01, 2026

Included in

Evolution Commons