The long-tailed vole (Microtus longicaudus) exhibits karyotypic variation in western North America. In the American Southwest, the species has a disjunct, relict distribution. However, karyotypes obtained from 20 specimens in 5 isolated mountain ranges (White Mountains, Arizona; Mount Taylor and the Sangre de Cristo, Jemez, and Mogollon mountains, New Mexico) exhibited no variation. These and previously reported karyotypes from the region had a diploid number (2n) of 56 and fundamental number (FN) of 84, which is the most commonly reported karyotype for the species.
Frey, Jennifer K.; Frey, Benjamin J.; and Moore, Dwight W.
"Karyotypes of the long-tailed vole (Microtus longicaudus) in isolated mountain ranges of the American Southwest,"
Western North American Naturalist: Vol. 69
, Article 13.
Available at: http://scholarsarchive.byu.edu/wnan/vol69/iss3/13