Here, Dr. Hamilton is presenting on a collaborative research project investigating the species limits and geographic structure with the North American Deer Mouse species complex. Since its original description in 1845, over 60 subspecies have been described based on various morphological and ecological characteristics, and the composition of species and subspecies within the deer mouse species group has been modified several times. Most recently, mitochondrial data have been used to support at least nine species within this species complex, with three species alone within the North American deer mouse. It is unknown if many of these taxa can be differentiated morphologically, and the extent of genetic species boundaries is likewise unknown. Verifying if multiple species exist with the deer mouse complex is vital given that species within this group are an established model system for evolutionary studies, including studies of zoonotic diseases (e.g., Hantavirus and Lyme disease). We investigate the species boundaries of lineages using genomic (ultraconserved elements) and computed tomography (CT) scanning technology of specimens from natural history collections across North America.