The Mouse

Oct 19, 2008 Features / Columnists, Interesting Creatures in Guyana

---

A mouse (plural mice) is a small animal that belongs to one of the thousands of rodent species, which is regarded to be the second most successful mammalian genus living on Earth today after humans.

Although mice may live up to two-and-a-half years in a laboratory, the average mouse in the wild lives only about four months, primarily due to heavy predation.

Cats, wild dogs, foxes, birds of prey, snakes and even certain kinds of insects have been known to prey heavily upon mice.

Nevertheless, due to their remarkable adaptability to almost any environment, and the ability to live commensally with humans, they have been surviving remarkably.

Mice are often considered harmful pests, damaging and eating crops and spreading diseases through their parasites and faeces.

In western North America, breathing dust that has come in contact with mouse faeces has been linked to the deadly hantavirus.

The original motivation for the domestication of cats is thought to have been for their predation of mice and their relatives, the rats.

Mice have been known to humans since antiquity and it is said that the Romans differentiated poorly between mice and rats, calling rats Mus Maximus (big mouse) and referring to mice as Mus Minimus (little mouse).

Mice range in size from 11 to 21 centimetres (cm) (4 to 8 inches) long which also includes a long tail.
They can weigh from .25 to 2 oz (7.1 to 57 g) and their coat colour can range from white to brown to grey.

Most mice have a pointed snout with long whiskers, round ears, and thin tails, and are known to scurry along the ground, while others have been seen hopping or jumping.

Breeding onset for mice is at about 50 days of age in both females and males, although females may have their first estrus at 25-40 days.

Mice are polyestrous and breed year round, with the process of ovulation being spontaneous. The duration of the estrous cycle is four to five days and estrus itself lasts about 12 hours, occurring in the evening. Vaginal smears are useful in timed matings to determine the stage of the estrous cycle.

Mating is usually nocturnal and may be confirmed by the presence of a copulatory plug in the vagina up to 24 hours post-copulation. The presence of sperm on a vaginal smear is also a reliable indicator of mating.

Female mice housed together tend to go into anestrus and do not cycle. If exposed to a male mouse or the pheromones of a male mouse, most of the females will go into estrus in about 72 hours.

This synchronization of the estrous cycle is known as the ‘Whitten effect’. The exposure of a recently bred mouse to the pheromones of a strange male mouse may prevent implantation (or pseudopregnancy), a phenomenon known as the ‘Bruce effect’.

The average gestation period is 20 days. A fertile postpartum estrus occurs 14-24 hours following parturition, and simultaneous lactation and gestation prolongs gestation 3-10 days due to delayed implantation. The average litter size is 10-12 during optimum production, but is highly strain dependent.

As a general rule, inbred mice tend to have longer gestation periods and smaller litters than outbred and hybrid mice.

The young are called pups and weigh 0.5–1.5 gramme (0.018–0.053 oz) at birth, are hairless, and have closed eyelids and ears. Cannibalism is uncommon, but females should not be disturbed during parturition and for at least two days postpartum.

Pups are weaned at three weeks of age with weaning weight being about 10–12 gramme (0.35–0.42 oz). If the postpartum estrus is not utilized, the female resumes cycling 2-5 days postweaning.

Newborn male mice are distinguished from newborn females by noting the greater anogenital distance and larger genital papilla in the male. This is best accomplished by lifting the tails of littermates and comparing perineums.

Mice are common experimental animals in biology and psychology, primarily because they are mammals, and so share a high degree of homology with humans.

They are the most commonly used mammalian model organism, more common than rats. The mouse genome has been sequenced, and virtually all mouse genes have human homologs.

They can also be manipulated in ways that would be considered unethical to do with humans. Other reasons why mice are used in laboratory research is that they are small, inexpensive, easily maintained, and can reproduce quickly.

Several generations of mice can be observed in a relatively short period of time and they are generally very docile if raised from birth and given sufficient human contact. However, certain strains have been known to be quite temperamental.
(Source: Wikipedia Free Online Encyclopedia)

---

---