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Rat

From Wikipedia, the free encyclopedia.

This is an article about wild rats; for pet rats, see fancy rat

Rats
Fossil Range: Early Pleistocene - Recent

Black Rat (Rattus rattus)

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Rodentia
Superfamily:	Muroidea*
Family:	Muridae
Subfamily:	Murinae
Genus:	Rattus Fischer de Waldheim, 1803

Species

50 species; see text
*Several subfamilies of Muroids
include animals called rats.

A rat is any one of about 56 different species of small, nearly omnivorous rodents belonging to the genus Rattus. The most well-known species are the Black Rat Rattus rattus and the Brown Rat Rattus norvegicus. The group is generally known as the old world rats or true rats, and originated in Asia. Rats are bigger than their relatives the mice, but seldom weigh over 500 grams in the wild. The common term rat is also used in the names of other small mammals which are not true rats. Examples include the North American pack rats, a number of species loosely called kangaroo rats, and a number of others. Other rats such as the Bandicoot rat Bandicota bengalensis are murine rodents related to the true rats, but are not members of the genus Rattus. The widely distributed and problematic commensal species of rats represent a minority in this diverse genus. Many species of rats are island endemics and some have become endangered due to habitat loss or competition with brown, black, or Polynesian rats.

In Western countries, many people keep domesticated rats as pets. These are of the species Rattus norvegicus, which originated in the grasslands of China and spread to Europe and eventually, in 1775, to the New World. Pet rats are descendants of Brown Rats bred for research, and may be called "fancy rats." But they are the same species as the common city "sewer" rat. Domesticated rats tend to be both more docile than their wild ancestors and more disease prone, presumably due to inbreeding.

Rats have a significant impact on food production. Estimates vary, but it is likely that anything between 1/5 and a 1/3 of the world's total output is eaten, spoiled or destroyed by rats and other rodents.

Brown Rat (Rattus norvegicus)

The common species are opportunistic survivors and often live with and near humans. The Black Plague is traditionally believed to have been caused by the micro-organism Yersinia pestis, carried by the rat flea Xenopsilia cheopis which preyed on Rattus rattus living in European cities of the day; it is notable that these rats were also victims themselves. It should perhaps also be noted that it has recently been suggested that neither rats nor infected fleas would have spread fast enough through Europe to have been a likely culprit. Regardless, rats are frequently blamed for damaging food supplies and other goods. Their reputation has carried into common parlance: in the English language, "rat" is an insult and "to rat on someone" is to betray them by denouncing a crime or misdeed they committed to the authorities. While modern wild rats can carry Leptospirosis and some other "zoonotic" conditions (those which can be transferred across species, to humans, for example), these conditions are in fact rarely found. Wild rats living in good environments are typically healthy and robust animals. Wild rats living in cities may suffer themselves from poor diet and internal parasites but do not largely spread disease to humans.

The rat makes a fine pet, known for its intelligence, playfulness and sociality. They are extremely clean. Rats can be taught entertaining tricks, as many other domesticated animals. As with any pet, it is best to seek a rat from a professional breeder rather than a pet store.

A pet rat

1 Rats in the laboratory
2 Rats in culture
3 See also
4 Taxonomy of Rattus
- 4.1 Species of Rats
5 Further reading and references
6 External links

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Rats in the laboratory

Like mice, rats (especially albino Rattus norvegicus) are frequently subjects of medical, psychological and other biological experiments. This is only partially due to their rapid growth to sexual maturity and because they are easily kept and bred in captivity. Rats are, in fact, socially, behaviorally, and in many ways physiologically similar to humans. Scientists have bred many strains or "lines" of rats specifically for experimentation. However, these lines are generally not transgenic because the easy techniques of genetic transformation that work in mice do not work in rats. This has frustrated many investigators, who regard many aspects of behavior and physiology in rats as more relevant to humans and easier to observe than in mice, but who wish to trace their observations to underlying genes. As a result, many researchers have been forced to study questions in mice and fruit flies (Drosophila melanogaster)[1] that might be better pursued in rats. In October 2003, however, researchers succeeded in cloning two laboratory rats by the problematic technique of nuclear transfer. This may lead to more rats being used as genetic research subjects.

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Rats in culture

In imperial Chinese culture, the rat (sometimes referred to as a mouse) is the first of the twelve animals of the Chinese zodiac. Consequently every twelfth year is known as a "year of the rat" in the Chinese calendar. People born in such years are expected to possess qualities associated with rats. These include creativity, honesty, generosity, ambition, a quick temper and wastefulness. "Rats" (i.e. people born in a year of the rat) are said to get along well with "monkeys" and "dragons," and to get along poorly with "horses."

In India in the northwestern city of Deshnoke, the Karni Mata Temple (the indogermanic roots of Mata traceable to the modern english "Mother") in reverence of an incarnation of Durga, the Goddess of War is devoted to the worship of rats. The holy animals are called "Kabbas" and many people undertake pilgrimage from afar to see these animals. It is believed the rats will be reincarnated into their next lives as Sadhus, Hindu holy men. The attending priests feed milk and grain to the animals of which also the pilgrims partake. Eating food that has been touched by the animals is considered a blessing.

The stereotypes associated with rats in Western civilization are less complimentary. Rats are seen as vicious, unclean, parasitic animals that steal food and spread disease. In one particularly infamous example, ravenous rats are used as a torture device in the novel Nineteen Eighty-Four, and in the movie 2 Fast 2 Furious. When anthropomorphized, rats are usually depicted as selfish, crude and untrustworthy, with the characters of The Secret of NIMH, Ratz, and Terry Pratchett's The Amazing Maurice and his Educated Rodents being the major exceptions. Describing a person as "rat-like" usually implies they are unattractive and suspicious. By contrast, mice are stereotyped as cute and bourgeois.

On the Isle of Man the word rat should be used with caution; even today many people may be shocked, and indeed offended upon its utterance. It is considered bad luck to mention this word. The origins of this superstition date far back, possibly to a time when many Manx people lived off the sea, where it was a sign of trouble when the rats were leaving the ship. Local alternatives include longtail, joey, queerfella, ringie and the Manx Gaelic word, roddan. In recent times, many young people have converted to saying "r-a-t", owing to the influence of British immigrants.

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Taxonomy of Rattus

The genus Rattus is a member of the giant subfamily Murinae. There are several other murine genera that are sometimes considered part of Rattus. These are: Lenothrix, Anonymomys, Sundamys, Kadarsanomys, Diplothrix, Margaretamys, Lenomys, Komodomys, Palawanomys, Bunomys, Nesoromys, Stenomys, Taeromys, Paruromys, Abditomys, Tryphomys, Limnomys, Tarsomys, Bullimus, Apomys, Millardia, Srilankamys, Niviventer, Maxomys, Leopoldamys, Berylmys, Mastomys, Myomys, Praomys, Hylomyscus, Heimyscus, Stochomys, Dephomys, and Aethomys.

The genus Rattus proper contains 56 species. A subgeneric breakdown of the species has been proposed, but does not include all species. The five groups are: