The white-footed mouse (Peromyscus leucopus) is a rodent native to North America from southern Canada to the southwestern United States and Mexico.

[5] They are timid and generally avoid humans, but they occasionally take up residence in ground-floor walls of homes and apartments, where they build nests and store food.

[16] Results of a landscape genomics study showed evidence of positive selection in mitochondrial genes of urban mice that are responsible for lipid and carbohydrate breakdown and digestion.

[16] This change in physical traits could be explained by the availability of higher-quality food sources in urban forests, which negates the need for long, powerful teeth.

A comparative transcriptome study found evidence of positive selection acting on the genes of urban mice that play major roles in detoxification and xenobiotic metabolism.

[18] This means that urban populations of white-footed mice that live in highly polluted environments uniquely benefit from an active demethylase enzyme that removes methyl groups from DNA.

Genes associated with spermatogenesis, sperm locomotion, and sperm-egg interactions in urban mice show a divergent pattern of regulation compared to their rural counterparts.

The divergence between rural and urban white-footed mice is especially prominent due to impeded gene flow between these populations, which is caused by landscape barriers including roads, highways, and pedestrian sidewalks.

[22] Monitoring the strength of immune defenses in P. leucopus is of special importance because they are commonly infected with dangerous pathogens such as hantaviruses and Borrelia burgdorferi.