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House mouse
Housemouse.jpg
General Information
Universe Real Life
Classification Mus musculus
Species Type Mouse
Homeworld Earth
Environment Human homes
Intelligence Non-sapient
Biochemistry Carbon-based
Biological Information
Lifespan Less than a year
Reproduction Sexual, viviparous
Average Weight 40–45 g (1+3⁄8–1+5⁄8 oz)
Average Length 7.5–10 cm (3–4 in)
Locomotion Quadrupedal
Feeding Behavior Omnivorous
Predators Domestic cats
Foxes
Weasels
Ferrets
Mongooses
Lizards
Snakes
Hawks
Falcons
Owls
Lineage Information
Descendant(s) Fancy mouse
Related Species Little Indian field mouse
Ryukyu mouse
Fawn-colored mouse
Cook's mouse
Cypriot mouse
Servant mouse
Sheath-tailed mouse
Macedonian mouse
Mus nitidulus
Steppe mouse
Algerian mouse
Earth-colored mouse
Cultural Information
Sociocultral characteristics
Scientific Taxonomy
Planet Earth
Domain Eukaryota
Kingdom Animalia
Subkingdom Eumetazoa
Infrakingdom Deuterostomia
Phylum Chordata
Subphylum Vertebrata
Infraphylum Gnathostomata
Superclass Tetrapoda
Class Mammalia
Subclass Theria
Infraclass Placentalia
Superorder Euarchontoglires
Order Rodentia
Suborder Myomorpha
Superfamily Muroidea
Family Muridae
Subfamily Murinae
Tribe Murini
Genus Mus
Subgenus Mus
Species M. musculus
Other Information
Status Least Concern
Creator God (debated)

The house mouse (Mus musculus) is one of the most common species of mice.

Characteristics[]

House mice have an adult body length (nose to base of tail) of 7.5–10 centimetres (3–4 in) and a tail length of 5–10 cm (2–4 in). The weight is typically 40–45 g (1+38–1+58 oz). In the wild they vary in color from grey and light brown to black (individual hairs are actually agouti coloured), but domesticated fancy mice and laboratory mice are produced in many colors ranging from white to champagne to black. They have short hair and some, but not all, sub-species have a light belly. The ears and tail have little hair. The hind feet are short compared to Apodemus mice, only 15–19 mm (91634 in) long; the normal gait is a run with a stride of about 4.5 cm (1+34 in), though they can jump vertically up to 45 cm (18 in). The voice is a high-pitched squeak. House mice thrive under a variety of conditions; they are found in and around homes and commercial structures, as well as in open fields and agricultural lands.

Newborn males and females can be distinguished on close examination as the anogenital distance in males is about double that of the female. From the age of about 10 days, females have five pairs of mammary glands and nipples; males have no nipples. When sexually mature, the most striking and obvious difference is the presence of testicles on the males. These are large compared to the rest of the body and can be retracted into the body.

The tail, which is used for balance, has only a thin covering of hair as it is the main peripheral organ of heat loss in thermoregulation along with—to a lesser extent—the hairless parts of the paws and ears. Blood flow to the tail can be precisely controlled in response to changes in ambient temperature using a system of arteriovenous anastomoses to increase the temperature of the skin on the tail by as much as 10 °C to lose body heat. Tail length varies according to the environmental temperature of the mouse during postnatal development, so mice living in colder regions tend to have shorter tails. The tail is also used for balance when the mouse is climbing or running, or as a base when the animal stands on its hind legs (a behavior known as tripoding), and to convey information about the dominance status of an individual in encounters with other mice.

In addition to the regular pea-sized thymus organ in the chest, house mice have a second functional pinhead-sized thymus organ in the neck next to the trachea.

Behavior[]

House mice usually run, walk, or stand on all fours, but when eating, fighting, or orienting themselves, they rear up on their hind legs with additional support from the tail – a behavior known as "tripoding". Mice are good jumpers, climbers, and swimmers, and are generally considered to be thigmotactic, i.e. usually attempt to maintain contact with vertical surfaces.

Mice are mostly crepuscular or nocturnal; they are averse to bright lights. The average sleep time of a captive house mouse is reported to be 12.5 hours per day. They live in a wide variety of hidden places near food sources, and construct nests from various soft materials. Mice are territorial, and one dominant male usually lives together with several females and young. Dominant males respect each other's territories and normally enter another's territory only if it is vacant. If two or more males are housed together in a cage, they often become aggressive unless they have been raised together from birth.

House mice primarily feed on plant matter, but are omnivorous. They eat their own faeces to acquire nutrients produced by bacteria in their intestines. House mice, like most other rodents, do not vomit.

Mice are generally afraid of rats which often kill and eat them, a behavior known as muricide. Despite this, free-living populations of rats and mice do exist together in forest areas in New Zealand, North America, and elsewhere. House mice are generally poor competitors and in most areas cannot survive away from human settlements in areas where other small mammals, such as wood mice, are present. However, in some areas (such as Australia), mice are able to coexist with other small rodent species.

Social behavior[]

The social behavior of the house mouse is not rigidly fixed into species-specific patterns but is instead adaptable to the environmental conditions, such as the availability of food and space. This adaptability allows house mice to inhabit diverse areas ranging from sandy dunes to apartment buildings.

House mice have two forms of social behaviour, the expression of which depends on the environmental context. House mice in buildings and other urbanized areas with close proximity to humans are known as commensal. Commensal mice populations often have an excessive food source resulting in high population densities and small home ranges. This causes a switch from territorial behaviour to a hierarchy of individuals. When populations have an excess of food, there is less female-female aggression, which usually occurs to gain access to food or to prevent infanticide. Male-male aggression occurs in commensal populations, mainly to defend female mates and protect a small territory. The high level of male-male aggression, with a low female-female aggression level is common in polygamous populations. The social unit of commensal house mouse populations generally consists of one male and two or more females, usually related. These groups breed cooperatively, with the females communally nursing. This cooperative breeding and rearing by related females helps increase reproductive success. When no related females are present, breeding groups can form from non-related females.

In open areas such as shrubs and fields, the house mouse population is known as noncommensal. These populations are often limited by water or food supply and have large territories. Female-female aggression in the noncommensal house mouse populations is much higher, reaching a level generally attributed to free-ranging species. Male aggression is also higher in noncommensal populations. In commensal populations, males come into contact with other males quite frequently due to high population densities and aggression must be mediated or the risk of injury becomes too great.

Both commensal and noncommensal house mouse males aggressively defend their territory and act to exclude all intruders. Males mark their territory by scent marking with urine. In marked territories, intruders showed significantly lower aggression than the territory residents. House mice show a male-biased dispersal; males generally leave their birth sites and migrate to form new territories whereas females generally stay and are opportunistic breeders rather than seasonal.

Senses and communication[]

Vision[]

The visual apparatus of mice is basically similar to that of humans but differs in that they are dichromats and have only two types of cone cells whereas humans are trichromats and have three. This means that mice do not perceive some of the colors in the human visual spectrum. However, the ventral area of the mouse retina has a much greater density of ultraviolet-sensitive cones than other areas of the retina, although the biological significance of this structure is unknown. In 2007, mice genetically engineered to produce the third type of cone were shown to be able to distinguish a range of colors similar to that perceived by tetrachromats.

Olfaction[]

House mice also rely on pheromones for social communication, some of which are produced by the preputial glands of both sexes. The tear fluid and urine of male mice also contains pheromones, such as major urinary proteins. Mice detect pheromones mainly with the vomeronasal organ (Jacobson's organ), located at the bottom of the nose.

The urine of house mice, especially that of males, has a characteristic strong odor. At least 10 different compounds, such as alkanes, alcohols, etc., are detectable in the urine. Among them, five compounds are specific to males, namely 3-cyclohexene-1-methanol, aminotriazole (3-amino-s-triazole), 4-ethyl phenol, 3-ethyl-2,7-dimethyl octane and 1-iodoundecane.

Odours from adult males or from pregnant or lactating females can speed up or retard sexual maturation in juvenile females and synchronise reproductive cycles in mature females (i.e. the Whitten effect). Odours of unfamiliar male mice may terminate pregnancies, i.e. the Bruce effect.

Tactile[]

Mice can sense surfaces and air movements with their whiskers which are also used during thigmotaxis. If mice are blind from birth, super-normal growth of the vibrissae occurs presumably as a compensatory response. Conversely, if the vibrissae are absent, the use of vision is intensified.

Life cycle and reproduction[]

Female house mice have an estrous cycle about four to six days long, with estrus itself lasting less than a day. If several females are held together under crowded conditions, they will often not have an estrus at all. If they are then exposed to male urine, they will come into estrus after 72 hours.

Male house mice court females by emitting characteristic ultrasonic calls in the 30 kHz–110 kHz range. The calls are most frequent during courtship when the male is sniffing and following the female; however, the calls continue after mating has begun, at which time the calls are coincident with mounting behaviour. Males can be induced to emit these calls by female pheromones. The vocalizations appear to differ between individuals and have been compared to bird songs because of their complexity. While females have the capability to produce ultrasonic calls, they typically do not do so during mating behaviour.

Following copulation, female mice will normally develop a copulation plug which prevents further copulation. The plug is not necessary for pregnancy initiation, as this will also occur without the plug. The presence or absence of the plug will not affect litter size either. This plug stays in place for some 24 hours. The gestation period is about 19–21 days, and they give birth to a litter of 3–14 young (average six to eight). One female can have 5 to 10 litters per year, so the mouse population can increase very quickly. Breeding occurs throughout the year. (However, animals living in the wild do not reproduce in the colder months, even though they do not hibernate.)

The pups are born blind and without fur or ears. The ears are fully developed by the fourth day, fur begins to appear at about six days and the eyes open around 13 days after birth; the pups are weaned at around 21 days. Females reach sexual maturity at about six weeks of age and males at about eight weeks, but both can copulate as early as five weeks.

Polygamy[]

Although house mice can be either monogamous or polygamous, they are most commonly polygamous. They generally show characteristics of mate-defense polygyny in that males are highly territorial and protective of their mates, while females are less agonistic. The communal nursing groups that result from these behaviors lead to lower numbers of infanticide since more females are able to protect greater numbers of offspring.

Evolutionary and behavioral consequences[]

Both evolutionary and behavioral consequences result from the polygamous nature of the house mouse. One consequence is the paternal investment, which is lower in polygamous mice than in mice that are monogamous. This occurs due to the fact that males spend more time involved in sexual competition than do females, leaving less time for paternal care. Polygamous male house mice spend less time alone with pups. They are also less likely and slower to retrieve lost pups than males of monogamous mice. In contrast, the maternal investment is similar between female mice that have mated once versus multiply.

The polygamous behavior of female house mice promotes sperm competition, which affects both male and female evolutionary fitness. Females who mate with multiple males tend to produce both pups in greater numbers, and with higher survival rates, increasing female fitness. Sperm competition that arises from polygamy favors males with faster, more motile sperm in higher numbers, increasing male fitness. The competitive aspect of insemination increases the frequency of polyandrous events and fertilizations. Polyandry has evolved to increase reproductive success. Male mating behavior is also affected in response to the practice of polygamous behavior. Compared to monogamous house mice, polygamous house mice mate for longer periods of time. This behaviour allows for an increase in both the transfer of sperm and paternity success, which in turn increases male fitness.

Polyandry[]

As opposed to polygyny, polyandrous behavior in females is the act of breeding with several males in the same season. Variation in number of males that females mate with occurs among a population. Polyandrous behavior is a common mating pattern in the subspecies Mus musculus musculus as well as its relative Mus musculus domesticus.

Polyandry occurs in 30% of all wild populations of house mice. Litters from multiple sires tend to be more genetically diverse than litters of single sires. Multiple paternity is also more common in larger populations than smaller populations, because there is a larger number of mates and more diverse mates to choose from. Within a population, males and females show different levels of multiple mating. Females show bias toward unrelated males rather than related males during sexual selection, resulting in more genetically diverse offspring and a reduction of inbreeding depression. Inbreeding depression increases genetic incompatibilities, levels of homozygosity, and the chance of expression of deleterious recessive alleles. Polyandry has been shown to increase offspring survival compared to monandry.

Evolutionary consequences[]

The fitness of females increases in polyandrous lines due to more genetic diversity and greater litter size.

Due to polyandry, males can be confused by the identity of new offspring. Multiple mating by females and paternity confusion can decrease rates of infanticide. If the males are uncertain if the offspring are theirs, they are less likely to kill the offspring.

Intrauterine insemination causes an evolutionary consequence resulting from polyandrous behavior. When multiple males mate with one female, there are multiple sets of sperm gametes in a female mouse. Offspring fertilized by multiple males can compete more strongly for mother's resources and can lead to a decrease in body size and variation in body size.

Genetics[]

A region of mouse chromosome 16 is associated with thyroid function in mice. However, mice with a knockout of 16 genes - 550kb - in this region produced a normal phenotype, excluding these genes in particular from the dysfunction being pursued in that study.

Life expectancy[]

House mice usually live less than one year in the wild, due to a high level of predation and exposure to harsh environments. In protected environments, however, they often live two to three years. The Methuselah Mouse Prize is a competition to breed or engineer extremely long-lived laboratory mice. As of 2005, the record holder was a genetically engineered mouse that lived for 1,819 days (5 years less 7 days). Another record holder that was kept in an enriched environment but did not receive any genetic, pharmacological, or dietary treatment lived for 1,551 days (4 years, 90 days).

Inbreeding violence[]

Since inbreeding is detrimental, it tends to be avoided. In the house mouse, the major urinary protein (MUP) gene cluster provides a highly polymorphic scent signal of genetic identity that appears to underlie kin recognition and inbreeding avoidance. Thus there are fewer matings between mice sharing MUP haplotypes than would be expected if there were random mating. Another mechanism for avoiding inbreeding is evident when a female house mouse mates with multiple males. In such a case, there appears to be egg-driven sperm selection against sperm from related males.

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