The rock pocket mouse (''Chaetodipus intermedius'') is one of 19

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of pocket mice in the

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

Chaetodipus ''Chaetodipus'' is a genus of pocket mice containing 17 species endemic to the United States and Mexico. Like other members of their family such as pocket mice in the genus '' Perognathus'', they are more closely related to pocket gophers than ...

''. It is sometimes grouped in the genus ''

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 The silky pocket mice are small animals with soft pelage, long tails, and small f ...

''.

Description

Found mainly in rocky outcrops in the

desert A desert is a landscape where little precipitation occurs and, consequently, living conditions create unique biomes and ecosystems. The lack of vegetation exposes the unprotected surface of the ground to denudation. About one-third of the la ...

s of the southwestern

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

and

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

, the rock pocket mouse is medium-sized (length ~18 cm, weight ~12–18g) and

nocturnal Nocturnality is a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite. Nocturnal creatur ...

. It eats mainly plant seeds and makes small burrows in soil close to or under rocks to evade

owl Owls are birds from the order Strigiformes (), which includes over 200 species of mostly solitary and nocturnal birds of prey typified by an upright stance, a large, broad head, binocular vision, binaural hearing, sharp talons, and feathers a ...

s, its main

predator Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

. The

breeding season Seasonal breeders are animal species that successfully mate only during certain times of the year. These times of year allow for the optimization of survival of young due to factors such as ambient temperature, food and water availability, and ch ...

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).

Taxonomy

Historically, rock pocket mice have been subdivided into as many as ten

subspecies In Taxonomy (biology), biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (Morphology (biology), morpholog ...

(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 (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

ic rock formations.

Example of natural selection

In 2003, scientists sampled

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

from both light- and dark-coloured rock pocket mice from areas in

Pinacate Peaks The Pinacate Peaks (Sierra Pinacate, ) are a volcanic group, group of volcanic peaks and cinder cones located mostly in the Mexican state of Sonora along the international border adjacent to the U.S. state of Arizona, surrounded by the vas ...

, Mexico and

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

, USA. In the Pinacate mice, they discovered a perfect association between different versions of the

Melanocortin-1 receptor The melanocortin 1 receptor (MC1R), also known as melanocyte-stimulating hormone receptor (MSHR), melanin-activating peptide receptor, or melanotropin receptor, is a G protein–coupled receptor that binds to a class of pituitary peptide hormones ...

(''Mc41r6'')

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

and coat colour. Subsequent studies demonstrated that there is strong selective pressure maintaining ''Mc1r''

allele An allele is a variant of the sequence of nucleotides at a particular location, or Locus (genetics), locus, on a DNA molecule. Alleles can differ at a single position through Single-nucleotide polymorphism, single nucleotide polymorphisms (SNP), ...

and coat colour frequencies across the short geographic distances between the light- and dark-coloured rock islands. Thus

melanism Melanism is the congenital excess of melanin in an organism resulting in dark pigment. Pseudomelanism, also called abundism, is another variant of pigmentation, identifiable by dark spots or enlarged stripes, which cover a large part of the bod ...

in rock pocket mice is considered a fabulous example of adaptation by

natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the Heredity, heritable traits characteristic of a population over generation ...

. 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 is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...

Description

Taxonomy

Example of natural selection

See also

References

Further reading