Rock pocket mouse
Encyclopedia
The rock pocket mouse, C. intermedius, is one of 19 species
of pocket mice in the genus
Chaetodipus. (It is sometimes grouped in the genus Perognathus
.)
Found mainly in rocky outcrops in the desert
s 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 owl
s, 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, basalt
ic 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 (Mc1r) 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 an elegant 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
.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of pocket mice in the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Chaetodipus. (It is sometimes grouped in the genus Perognathus
Perognathus
Perognathus is a genus of pocket mouse. Like other members of their family they are more closely related to pocket gophers than to true mice.-Characteristics:...
.)
Found mainly in rocky outcrops in the desert
Desert
A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...
s of the southwestern United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
, the rock pocket mouse is medium-sized (length ~18 cm, weight ~12–18g) and nocturnal
Nocturnal animal
Nocturnality is an animal behavior characterized by activity during the night and sleeping during the day. The common adjective is "nocturnal"....
. It eats mainly plant seeds and makes small burrows in soil close to or under rocks to evade owl
Owl
Owls are a group of birds that belong to the order Strigiformes, constituting 200 bird of prey species. Most are solitary and nocturnal, with some exceptions . Owls hunt mostly small mammals, insects, and other birds, although a few species specialize in hunting fish...
s, its main predator. The breeding season
Breeding season
The breeding season is the most suitable season, usually with favourable conditions and abundant food and water, for breeding among some wild animals and birds . Species with a breeding season have naturally evolved to have sexual intercourse during a certain time of year in order to achieve the...
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
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
(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, basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic rock formations.
In 2003, scientists sampled DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
from both light- and dark-coloured rock pocket mice from areas in Pinacate Peaks
Pinacate Peaks
The Pinacate Peaks are a volcanic group of volcanic peaks and cinder cones located mostly in the Mexican state of Sonora along the international border adjacent to the U.S...
, Mexico and New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
, USA. In the Pinacate mice, they discovered a perfect association between different versions of the Melanocortin-1 receptor (Mc1r) gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
and coat colour . Subsequent studies demonstrated that there is strong selective pressure maintaining Mc1r allele
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
and coat colour frequencies across the short geographic distances between the light- and dark-coloured rock islands.
Thus melanism
Melanism
Melanism is an undue development of dark-colored pigment in the skin or its appendages, and the opposite of albinism. It is also the medical term for black jaundice.The word is deduced from the , meaning black pigment....
in rock pocket mice is considered an elegant example of adaptation by natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
. 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
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
.
Further reading
- Desert Mice Offer New Lessons on Survival of the Fittest, news article from the University of ArizonaUniversity of ArizonaThe University of Arizona is a land-grant and space-grant public institution of higher education and research located in Tucson, Arizona, United States. The University of Arizona was the first university in the state of Arizona, founded in 1885...
. - Rock pocket mouse, profile from the Smithsonian Natural History Museum.