The North American deer mouse Peromyscus maniculatus is one of the most widespread and geographically variable rodent species in North America, with a range extending from Canada south across most of the United States and into Mexico. Not surprisingly, there is some limited evidence that cryptic lineages may exist across this large geographic area. Determining if multiple species exist within P.maniculatus is vital given that this species is a known reservoir for multiple diseases and is often used as a model system for evolutionary and ecological studies. Dr. Light will discuss her recent research in the genus Peromyscus, including her attempts to differentiate and delimit cryptic lineages within P.maniculatus using morphological and molecular data from specimens housed in natural history collections.