Rat

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

Rats
Conservation status: Secure

Black Rat (Rattus rattus)

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Rodentia
Superfamily:	Muroidea*
Family:	Muridae
Subfamily:	Murinae
Genus:	Rattus

Species

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

A rat is a small nearly omnivorous rodent of the genus Rattus which comprises 56 different species of what is commonly known as the Old World Rats or true rats who originated in Asia. Rats are bigger than their relatives the mice, but seldom weigh over 500 grams. The common term rat is also used in the names of other small mammals which are not true rats. Examples include the North American Wood or pack rat, a number of species loosely called kangaroo rats, the Bandicoot Rat, Bandicota bengalensis and a number of others.

In Western countries, many people keep domesticated rats as pets. These are of the species Rattus Norvegicus -- the Norway Rat, Asian Black Rat, Black Rat or Barn Rat -- who originated in the grasslands of China and spread to Europe and eventually, in 1775, to the New World. Pet rats are descendants of Norway 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.

Contents

1 Varieties

2 Rats in the laboratory

5 Further reading and references

6 External links

Varieties

There are 56 species of Old World Rat, the most well-known of which are Norvegicus; the Black Rat, Rattus rattus, also known as the Asian Brown Rat, the Brown Rat, the Ship Rat and the Roof Rat; and the Polynesian Rat, Rattus exulans.

These three common species are survivally opportunistic and often live with and near humans which has incidentally given them a poor reputation. The Black Plague is 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 noteable that these Roof Rats were not carriers, but were also victims themselves. Rats are also 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 show as perfectly healthy and robust animal specimens. Wild rats living in cities may suffer themselves from poor diet and internal parasites but do not largely spread disease to humans.

The Norway Rat makes a fine pet, known for their intelligence and playfulness. They are extremely clean and have an excellent sense of humor. As with any pet, it is best to seek a rat from a professional breeder rather than a pet store.

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. Rat are, in fact, socially, behaviorally and in many ways physiologically similar to humans. The species Rattus norvegicus albinus has a dental formula of ICPM 1/1, 0/0, 0/0, 3/3. 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 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.

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."

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. When anthropomorphized, rats are usually depicted as selfish, crude and untrustworthy, with the characters of The Secret of NIMH being the major exception. Describing a person as ratlike usually implies they are unattractive and suspicious. By contrast, mice are stereotyped as cute and bourgeois.

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: