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Brief Summary

    Cactus mouse: Brief Summary
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    The cactus mouse (Peromyscus eremicus) is a species of rodents in the family Cricetidae. It is one species of a closely related group of common mice often called deer mice. Cactus mice are small, between 18 and 40 g in weight. Females weigh slightly more than males and are significantly larger in body length, ear length, length of mandible, and bullar width of skull. Cactus mice can be identified by having naked soles on their hind feet and almost naked tails, which are usually the same length or longer than the animals' body length. Their ears are nearly hairless, large, and membranous. Their fur is long and soft; coloration varies between subspecies and between different populations. Color of fur varies from ochre to cinnamon, with white ventral areas, and the sides and top of head slightly grayish. Females tend to be slightly paler in color than males, while juveniles appear more gray than their parents.

Comprehensive Description

Distribution

    Distribution
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    Peromyscus eremicus is found in the southwestern United States, northern Mexico, Baja California and several nearby islands (Nowak 1991). The subspecies Peromyscus eremicus eremicus can be found farther north in Utah (Species Information Library, Peromyscus eremicus eremicus 1994).

    Biogeographic Regions: nearctic (Native )

Morphology

    Morphology
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    The range of masses given includes both male and females, as little research has been conducted on sexual dimorphisms in size. Average body length (not including the tail) is 8.0 to 9.0 centimeters and the average tail length is 10.0 to 14.0 centimeters (Parker 1990). This species is noted for its unusually long tail. A possible function for such a long tail is body temperature regulation (Hanney 1975). The color of the thick pelage appears to vary. Parker remarks that Peromyscus eremicus has a pale gray back (1990). The Species Information Library, however, reports that species have been found in New Mexico with a spectrum of fur shades between pale yellowish and blackish (1994). A possible explanation is that two subspecies, one with darker fur (Peromyscus eremicus anthonyi) and lighter fur (Peromyscus eremicus eremicus) have interbred in New Mexico. Nowak describes the underparts of the cactus mouse as white or near-white (1991). The tail is usually less haired than that of other mice in its genus. Cactus mice have naked soles on their hind feet, which distinguish them from other southwestern Peromyscus species. Facial and skull characteristics are also important in distinguishing the cactus mouse from other Peromyscus mice. Peromyscus eremicus has small ears and one to two upper molars with usually one mesoloph. The zygomatic arches of the skull are weak and not flared out and the auditory bulla are not greatly inflated (Species Information Library Peromyscus eremicus 1994). The nasal branches of the premaxillae extend posteriorly behind the nasals.

    Range length: 80 to 90 mm.

    Other Physical Features: endothermic ; heterothermic ; homoiothermic; bilateral symmetry

    Sexual Dimorphism: sexes alike

    Average mass: 25 g.

    Average basal metabolic rate: 0.173 W.

Habitat

    Habitat
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    Peromyscus eremicus primarily lives in desert areas with cacti, hence the name cactus mouse. It lives in steppes and semi-arid deserts. Peromyscus eremicus may be found in the rocky foothills of desert mountain ranges. Subspecies found in Utah (Peromyscus eremicus eremicus) can be semi-arboreal and inhabit shrubs (Species Information Library 1994). Cactus mice build nests in self-dug tunnels, lodges of other rodents, brickwork buildings, and piles of rock or brushwood (Parker 1990). Price and Waser's study of the post-fire reinhabition of an area of California costal sage scrub revealed Peromyscus eremicus preference for rock and brush habitats over open areas and debris (1984).

    Habitat Regions: temperate ; terrestrial

    Terrestrial Biomes: desert or dune ; chaparral

Trophic Strategy

    Trophic Strategy
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    Cactus mice are opportunistic omnivores. They eat mainly fruits and blossoms of shrubs and annual seeds such as hackberry (Ulmaceae) and mesquite (Leguminoseae) (Species Information Library, Peromyscus eremicus eremicus 1994). Pinus and Juniperus seeds are eaten during the winter. In addition, cactus mice eat insects, leaves, and green vegetation (Parker 1990).

    Animal Foods: insects

    Plant Foods: leaves; seeds, grains, and nuts; fruit; flowers

    Primary Diet: omnivore

Associations

    Associations
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    Cactus mice are important seed predators and form an important prey base for a variety of predators in their desert habitats.

    Associations
    provided by Animal Diversity Web

    Cactus mice, like other Peromyscus species, are abundant small mammals in the areas in which they live. They form an important prey base for predators such as owls, rattlesnakes, foxes, and other predators. They can run quickly and are generally secretive and nocturnal, which helps to protect them from some predation. Their ability to reproduce rapidly also means that populations respond robustly to heavy predation pressure.

    Known Predators:

    • rattlesnakes Crotalus)
    • owls (Strigiformes)
    • foxes (Vulpes)

    Anti-predator Adaptations: cryptic

Behavior

    Behavior
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    The vocalizations of Peromyscus species have been described as thin squeaks and shrill buzzings. Most species, when excited, thump their forefeet rapidly upon the ground to produce a drumming noise (Nowak 1991). Like other Peromyscus species, cactus mice have keen vision and hearing and use chemical cues extensively in communication.

    Communication Channels: visual ; chemical

    Perception Channels: visual ; tactile ; acoustic ; chemical

Life Expectancy

    Life Expectancy
    provided by Animal Diversity Web

    Like other Peromyscus, most cactus mice live about 1 year.

    Average lifespan
    Status: wild:
    1 years.

    Average lifespan
    Status: captivity:
    7.4 years.

Reproduction

    Reproduction
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    Mating systems in cactus mice are not well understood. Like other Peromyscus species they are likely to have a promiscuous mating system.

    The gestation period for Peromyscus eremicus is 20 to 25 days. Litter size is 1 to 4 offspring and average weight at birth is 2.1 to 2.9 grams (Parker 1990). Females may have up to 4 litters per year. The female has two pairs of teats rather than three, which has been suggested to correlate with the number of offspring (Parker 1990). The weaning period is unknown. Females reach sexual maturity after about two months, and the age of male sexual maturity is unknown. The average age for the female cactus mouse's first estrus is 39.2 days (Nowak 1991). Females have been observed to reproduce continuously and year round, and specifically during January, February, June, and September in central Arizona (Spotorno 1992).

    Male Peromyscus eremicus have a simple penis, distinct from the complex penis of some other murids. The os baculum is simple, lacking the three distal prongs typical of complex penes. Young cactus mouse penes were found to have three bluish cartilaginous condensations near the tip of a well-ossified baculum. One condensation was located at the apex and two were located laterally, where the normal distal prongs in a complex penis would occur (Spotorno 1992). This characteristic is not only distinguishing, but it suggests that possession of a 3-pronged baculum may be primitive. The penis is nevertheless broad, and its size has been suggested to increase "locking" during 3.5 percent of copulations (Species Information Library Peromyscus eremicus 1994). Additionally, bone-ossification and sexual maturity are both controlled by testosterone.

    Breeding interval: Cactus mice can have multiple litters in a year.

    Breeding season: Breeding occurs throughout the year.

    Range number of offspring: 1 to 4.

    Range gestation period: 20 to 25 days.

    Average age at sexual or reproductive maturity (female): 2 months.

    Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous

    Average birth mass: 2.33 g.

    Average number of offspring: 2.6.

    Average age at sexual or reproductive maturity (female)
    Sex: female:
    129 days.

    Young cactus mice are born with their ears and eyes closed. The ears open in the first day after birth and the eyes open in 11 to 15 days. Females nurse and care for their young in their nest until they are weaned, probably within a few weeks of birth. Juveniles go through their first molt at 5 weeks old.

    Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female)

Conservation Status

    Conservation Status
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    Cactus mice are generally abundant within their range.

    US Federal List: no special status

    CITES: no special status

    IUCN Red List of Threatened Species: least concern

Benefits

    Benefits
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    No negative effects on humans are known. However, the closely related species Peromyscus maniculatus is harmful to forest regeneration because it eats seeds, particularly those of conifers (Nowak 1991). Cactus mice are known to eat Pinus and Juniperus seeds as well, so it makes sense that they could be an additional threat to forest regeneration. They also prey on insects pests of forests, so the impact of their seed predation may be balanced by their impact on insects.

    Benefits
    provided by Animal Diversity Web

    Peromyscus eremicus is an excellent model for physiological and genetic studies. It is clean, lives well in cages, and has a high rate of productivity (Nowak 1991).

    Positive Impacts: research and education

Notes

Other Articles

    Untitled
    provided by Animal Diversity Web

    Peromyscus eremicus is in the subgenus Haplomylomys. Cactus mice have two main adaptations for their desert habitat, a lowered metabolism and an ability to enter torpor when deprived of food and water. To investigate the claim that the low metabolism of desert rodents is maintained by low thyroid gland activity, Hulbert et al. (1985) measured the level of plasma thyroxine in heteromyids versus cricetids (including Peromyscus eremicus). Their results suggested that the environment affects thyroxine levels, since all species displayed lower metabolisms in a desert versus a coastal habitat. In extreme conditions such as deprivation of both water and food, cactus mice may enter torpor within twelve hours. Below thirty degrees Celsius, there is a depression in body temperature and oxygen consumption. At temperatures lower than fifteen degrees Celsius, cactus mice enter torpor more slowly (Species Information Library Peromyscus eremicus 1994). This effect of temperature on torpor has been suggested as a possible explanation for their southern distribution. The desert adaptation of lowered metabolism comes with a cost. A study of five species of Peromyscus established that for female Peromyscus eremicus, the basal rate of metabolism is correlated to the rate it processes energy for reproduction during lactation (Glazier 1985). In practical terms, this means that the higher the rate of metabolism for the mother and the young, the faster food can be transformed into milk and eventually offspring growth. Thus, Peromyscus eremicus's drier habitat limits it to a litter size of about two to three offspring (Parker 1990).