House Mouse INTRODUCED - CONFIRMED (Mammals of Yourka Reserve)

House Mouse INTRODUCED - CONFIRMED

Mus musculus

Summary ⁴

The house mouse (Mus musculus) is a small mammal of the order Rodentia, characteristically having a pointed snout, large rounded ears, and a long and almost hairless tail. It is one of the most abundant species of the genus Mus. Although a wild animal, the house mouse has benefited significantly from associating with human habitation to the point that truly wild populations are significantly less common than the semi-tame populations near human activity.

Characteristics ⁵

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 .mw-parser-output .frac{white-space:nowrap}.mw-parser-output .frac .num,.mw-parser-output .frac .den{font-size:80%;line-height:0;vertical-align:super}.mw-parser-output .frac .den{vertical-align:sub}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}40–45 g (1+3⁄8–1+5⁄8 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 (9⁄16–3⁄4 in) long; the normal gait is a run with a stride of about 4.5 cm (1+3⁄4 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.^{[citation needed]}

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.^{[citation needed]}

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 (10 K; 18 °F) 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 behaviour 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 ⁵

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.^{[citation needed]}

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.^{[citation needed]} 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.^{[citation needed]}

House mice primarily feed on plant matter, but are omnivorous.^{[citation needed]} 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.

Life cycle and reproduction ⁵

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^{[citation needed]} 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 mating 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.

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.

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.

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.

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.

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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