Sinaloan pocket mouse

Sinaloan pocket mouse
State of Sinaloa in Mexico
Conservation status
Least Concern  (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Rodentia
Family:	Heteromyidae
Genus:	Chaetodipus
Species:	C. pernix
Binomial name
Chaetodipus pernix (J. A. Allen, 1898)

The Sinaloan pocket mouse, C. pernix, is one of 17 species of pocket mice in the genus Chaetodipus. Two subspecies of C. pernix are recognized, C. p. pernix and C. p. rostratus, all are endemic to Mexico.

This small mouse lives among shrubs and has a wide range of coat colors due to variations in the environment within a population.

Description

The Sinaloan pocket mouse is one of the smallest in the genus Chaetodipus with a total length of less than 200mm. Their skull is narrow with an elongated nose and medium sized ears. C. pernix has a thinly haired tail that is longer than the body length. Their coat color is variable (usually yellowish-brown), but always darker on the back and lighter on the sides and belly. Their diet consists of grains and seeds. The average litter size is seven.

Color Polymorphism

Many different coat colors, or polymorphisms, are seen between species of pocket mice and even within the same population. These differences in coat color are due to genetic variation and adapting to varying environments. Many hypotheses exist for why there is so much variation between coat colors in mammals. In 2005 Caro explained color patterning using three main hypotheses: concealment, communication, and physiological processes.

Coloration in pocket mice evolved mostly for concealment and physiological processes. The owl is the largest predator of pocket mice. Mice with coat colors that better match their environment have a better chance of going unnoticed by predators and surviving. This is why pocket mice living in different environments have different coat colors; to better blend with their surroundings. The Sinaloan pocket mouse usually has a yellow-brown coat with black hairs because they live in a sandy environment under shrubs. This is very different from the Rock pocket mouse that usually has a grey or black coat color.

As noted above, pocket mice almost always have a lighter belly and sides compared to the darker color of their back. This color pattern also helps in concealment from predators and is called countershading. This is seen in many mammal species as it helps reduce the appearance of their shadow in sunny environments. Pocket mice developed this color pattern to again, avoid predation from owls in their sunny, desert habitat.

The coat color of the Sinaloan pocket mouse also developed to help regulate physiological processes of the body. Sinaloan pocket mice live in the desert and are subject to very high heat and levels of sunlight. Having a lighter color coat in this environment is beneficial to help regulate body temperature. Multiple aspects of the environment put selective pressures on pocket mice to adapt their coat colors.

Genetic Basis

The genetic difference for varying coat colors is controlled largely by two proteins in pocket mice. First, the melanocortin-1-receptor (MC1R) is a G protein-coupled receptor responsible for activating the pathway that causes melanocytes to produce the pigment eumelanin giving hair a black or brown color. Second is the agouti-signaling protein, which is an antagonist of MC1R. Agouti expression causes decreased levels of eumelanin production and increased levels of pheomelanin, giving hair a red color. Variation in the environment can cause proteins to be expressed differently producing variation in coat color between two different environments.

Range and Habitat

C. pernix mostly lives in the coastal plain of Sinaloa state within Mexico, which extends from Southern Sonora to Northern Nayarit. Their habitat consists mostly of small trees, shrubs, and cacti. Sinaloan pocket mice are found on sandy soil, living under low bushes or dense networks of vines and grasses. Their habitat does not contain any rock material, unlike in its sister species, the rock pocket mouse.

References

• Patton, J. L. 2005. Family Heteromyidae. Pp. 844-858 in Mammal Species of the World a Taxonomic and Geographic Reference. D. E. Wilson and D. M. Reeder eds. Johns Hopkins University Press, Baltimore.