Rock pocket mouse
|Rock pocket mouse|
Found mainly in rocky outcrops in the deserts of the southwestern United States and Mexico, the rock pocket mouse is medium-sized (length ~18 cm, weight ~12–18g) and nocturnal. It eats mainly plant seeds and makes small burrows in soil close to or under rocks to evade owls, its main predator. The breeding season spans a few months, starting in February or March, and the litter size is typically between three and six. As with most pocket mice, the tail is longer than the body (~10 cm).
Historically, rock pocket mice have been subdivided into as many as ten subspecies (Benson 1933; Dice and Blossom 1937) based on geographical distribution and coat colour. Most rock pocket mouse populations have light, tawny fur consistent with the colour of the desert rocks on which they live. However, darker coloured rock pocket mice are found living amid black, basaltic rock formations.
In 2003, scientists sampled DNA from both light- and dark-coloured rock pocket mice from areas in Pinacate Peaks, Mexico and New Mexico, USA. In the Pinacate mice, they discovered a perfect association between different versions of the Melanocortin-1 receptor (Mc41r6) gene and coat colour . Subsequent studies demonstrated that there is strong selective pressure maintaining Mc1r allele and coat colour frequencies across the short geographic distances between the light- and dark-coloured rock islands.
Thus melanism in rock pocket mice is considered a fabulous example of adaptation by natural selection. Changes in the Mc1r gene sequence are not responsible for the colour difference in the mice sampled from New Mexico, however, leading the researchers to conclude that the almost identical dark coat colours developed multiple times in rock pocket mice, an example of convergent evolution.
- Linzey, A.V., Timm, R., Álvarez-Castañeda, S.T., Castro-Arellano, I. & Lacher, T. (2008). Chaetodipus intermedius. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 18 January 2009. Database entry includes a brief justification of why this species is of least concern
- "ITIS Standard Report Page: Perognathus intermedius".
- Nachman MW, Hoekstra HE, D'Agostino SL (April 2003). "The genetic basis of adaptive melanism in pocket mice". Proc. Natl. Acad. Sci. U.S.A. 100 (9): 5268–73. doi:10.1073/pnas.0431157100. PMC 154334. PMID 12704245.
- Hoekstra HE, Drumm KE, Nachman MW (June 2004). "Ecological genetics of adaptive color polymorphism in pocket mice: geographic variation in selected and neutral genes". Evolution 58 (6): 1329–41. PMID 15266981.
- Hoekstra HE, Nachman MW (May 2003). "Different genes underlie adaptive melanism in different populations of rock pocket mice". Mol. Ecol. 12 (5): 1185–94. doi:10.1046/j.1365-294X.2003.01788.x. PMID 12694282.
- Desert Mice Offer New Lessons on Survival of the Fittest, news article from the University of Arizona.
- Rock pocket mouse, profile from the Smithsonian Natural History Museum.