Rat

Rats Temporal range: Early Pleistocene – Recent
The common brown rat (Rattus norvegicus)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Rodentia
Superfamily:	Muroidea
Family:	Muridae
Subfamily:	Murinae
Genus:	Rattus Fischer de Waldheim, 1803
Species
64 species
Synonyms
Stenomys Thomas, 1910

Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus. Many members of other rodent genera and families are also referred to as rats, and share many characteristics with true rats.

Rats are typically distinguished from mice by their size; rats are generally large muroid rodents, while mice are generally small muroid rodents. The muroid family is very large and complex, and the common terms rat and mouse are not taxonomically specific. Generally, when someone discovers a large muroid, its common name includes the term rat, while if it is small, the name includes the term mouse. Scientifically, the terms are not confined to members of the Rattus and Mus genera, for example, the pack rat and cotton mouse.

Species and description

The best-known rat 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 most Old World mice, which are their relatives, but seldom weigh over 500 grams (1.1 lb) in the wild.

The 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 others. Rats such as the bandicoot rat (Bandicota bengalensis) are murine rodents related to true rats, but are not members of the genus Rattus. Male rats are called bucks, unmated females are called does, pregnant or parent females are called dams, and infants are called kittens or pups. A group of rats is either referred to as a pack or a mischief.

A rat in a city street

Statue of a rat in Patan (Nepal)

The common species are opportunistic survivors and often live with and near humans; therefore, they are known as commensals. They may cause substantial food losses, especially in developing countries. However, the widely distributed and problematic commensal species of rats are 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 the brown, black or Polynesian rat.

Wild rodents, including rats, can carry many different zoonotic pathogens, such as Leptospira, Toxoplasma gondii, and Campylobacter. The Black Death is traditionally believed to have been caused by the micro-organism Yersinia pestis, carried by the tropical rat flea ( Xenopsylla cheopis) which preyed on black rats living in European cities during the epidemic outbreaks of the Middle Ages; these rats were used as transport hosts. Other zoonotic diseases linked to pest rodents include classical swine fever and foot-and-mouth disease.

The average lifespan of any given rat depends on which species is being discussed, but many only live about a year due to predation.

The black and brown rats diverged from other Old World rats during the beginning of the Pleistocene in the forests of Asia.

Pets

A domesticated rat

Specially bred rats have been kept as pets at least since the late 19th century. Pet rats are typically variants of the species brown rat, but black rats and giant pouched rats are also known to be kept. Pet rats behave differently from their wild counterparts depending on how many generations they have been kept as pets. Pet rats do not pose any more of a health risk than pets such as cats or dogs. Tamed rats are generally friendly and can be taught to perform selected behaviors.

Subjects for scientific research

A laboratory rat strain, known as a Zucker rat, is bred to be genetically prone to diabetes, the same metabolic disorder found among humans.

In 1895, Clark University in Worcester, Massachusetts (United States) established a population of domestic albino brown rats to study the effects of diet and for other physiological studies. Over the years, rats have been used in many experimental studies, which have added to our understanding of genetics, diseases, the effects of drugs, and other topics that have provided a great benefit for the health and well-being of humankind. Laboratory rats have also proved valuable in psychological studies of learning and other mental processes (Barnett, 2002), as well as to understand group behaviour and overcrowding (with the work of John B. Calhoun on behavioural sink). A 2007 study found rats to possess metacognition, a mental ability previously only documented in humans and some primates.

Domestic rats differ from wild rats in many ways. They are calmer and less likely to bite; they can tolerate greater crowding; they breed earlier and produce more offspring; and their brains, livers, kidneys, adrenal glands, and hearts are smaller (Barnett 2002).

Brown rats are often used as model organisms for scientific research. Since the publication of the rat genome sequence, and other advances, such as the creation of a rat SNP chip, and the production of knockout rats, the laboratory rat has become a useful genetic tool, although not as popular as mice. When it comes to conducting tests related to intelligence, learning, and drug abuse, rats are a popular choice due to their high intelligence, ingenuity, aggressiveness, and adaptability. Their psychology, in many ways, seems to be similar to humans. Entirely new breeds or "lines" of brown rats, such as the Wistar rat, have been bred for use in laboratories. Much of the genome of Rattus norvegicus has been sequenced.

Intelligence

A Rat in a suburb of Vancouver.

Because of the ability to learn, rats were early on investigated to see whether they may exhibit general intelligence like larger or more complex animals. A 1929 study did not find a g factor, nor did a 1990 work; a 1935 study did:

Robert Thorndike, for example, provided strong evidence for g in rats by the use of a variety of tests such as mazes, problem-solving tasks, and simple avoidance conditioning (Thorndike 1935). Performances tended to correlate across tasks, with stronger associations found between mazes and problem-solving than with simple avoidance tasks. Thorndike (1935) also reviewed a dozen earlier studies which also suggested that the highest correlations are found between more complex problem-solving tasks. However, it should be noted that there were other contemporary studies that found split or near zero-order correlation matrices for other populations of rats across cognitive batteries (see Royce 1950).

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In 1993, Anderson measured rat performance and factor analysis produced a g, and also correlations with rat brain size (like in humans and primates). Locurto & Scanlon 1998, Matzel et al. 2003, Matzel et al. 2004, Kolata et al. 2009 and Matzel et al. 2011 replicated the factor (but did not investigate brain size); 2003 Locurto et al., 2006 Locurto et al. in contrast found their factor analysis giving 4 factors rather than 1.

Social intelligence

Controlled study found rats are actively prosocial. They demonstrate altruistic behaviour to other rats in experiments.

Food

Rat meat dishes in Yangshuo, Guangxi, China

Rat meat is a food that, while taboo in some cultures, is a dietary staple in others. Taboos include fears of disease or religious prohibition, but in many places, the high number of rats has led to their incorporation into the local diets.

In some cultures, rats are or have been limited as an acceptable form of food to a particular social or economic class. In the Mishmi culture of India, rats are essential to the traditional diet, as Mishmi women may eat no meat except fish, pork, wild birds and rats. Conversely, the Musahar community in north India has commercialised rat farming as an exotic delicacy. In the traditional cultures of the Hawaiians and the Polynesians, rat was an everyday food for commoners. When feasting, the Polynesian people of Rapa Nui could eat rat meat, but the king was not allowed to, due to the islanders' belief in his "state of sacredness" called tapu. In studying precontact archaeological sites in Hawaii, archaeologists have found the concentration of the remains of rats associated with commoner households accounted for three times the animal remains associated with elite households. The rat bones found in all sites are fragmented, burned and covered in carbonized material, indicating the rats were eaten as food. The greater occurrence of rat remains associated with commoner households may indicate the elites of precontact Hawaii did not consume them as a matter of status or taste.

Bandicoot rats are an important food source among some peoples in Southeast Asia, and the United Nations Food and Agriculture Organization estimated rat meat makes up half the locally produced meat consumed in Ghana, where cane rats are farmed and hunted for their meat. African slaves in the American South were known to hunt wood rats (among other animals) to supplement their food rations, and Aborigines along the coast in southern Queensland, Australia, regularly included rats in their diet.

Ricefield rats ( Rattus argentiventer) have traditionally been used as food in rice-producing regions such as Valencia, as immortalized by Vicente Blasco Ibáñez in his novel Cañas y barro. Along with eel and local beans known as garrafons, rata de marjal is one of the main ingredients in traditional paella (later replaced by rabbit, chicken and seafood). Ricefield rats are also consumed in the Philippines, the Isaan region of Thailand, and Cambodia. In late 2008, Reuters reported the price of rat meat had quadrupled in Cambodia, creating a hardship for the poor who could no longer afford it.

Elsewhere in the world, rat meat is considered diseased and unclean, socially unacceptable, or there are strong religious proscriptions against it. Islam and Kashrut traditions prohibit it, while both the Shipibo people of Peru and Sirionó people of Bolivia have cultural taboos against the eating of rats.

Rats are a common food item for snakes, both in the wild, and as pets. Captive-bred ball pythons, in particular, are fed a diet of mostly rats. Rats, as food items, are available from many suppliers individual snake owners, as well as to large reptile zoos. In Britain, the government in 2007 ruled out the feeding of any live mammal to another animal. The rule says the animal must be dead (frozen) then given to the animal to eat. The rule was put in to place mainly because of the pressure of the RSPCA and people who found it cruel.

Medicine

Rats can serve as zoonotic vectors for certain pathogens and thus cause disease, such as Lassa fever, leptospirosis and Hantavirus infection. However the rat is almost never directly responsible for the pathogen. Though it is commonly believed that R. rattus is responsible for the outbreak of bubonic plague the European citizens are to blame. After throwing waste into the street the rats moved where it was easy to find food. The rat flea then spread the plague from there. It is estimated that as many, if not more rats died from the plague than people.

Odour detection

Rats have a keen sense of smell and are easy to train. These characteristics have been employed, for example, by the APOPO Norwegian NGO, which trains rats (specifically African giant pouched rats) to detect landmines and diagnose tuberculosis through smell.

Rats as pests

Rats have long been considered deadly pests. Once considered an modern myth, the rat plague in India has now been verified. Indeed every fifty years, armies of bamboo rats descend upon rural areas and devour everything in their path. Rats have long been held up as the chief villain in the spread of the Bubonic Plague, however recent studies show that they alone could not account for the rapid spread of the disease through Europe in the Middle Ages. Still, the Centre for Disease Control does list nearly a dozen diseases directly linked to rats. Most urban areas battle rat infestations. Rats in New York City are famous for their size and prevalence. Some statistics claim there are more rats than people in the Big Apple and that they are pretty wily characters. New York has specific regulations for getting rid of rats—multi-family residences and commercial businesses must use a specially trained and licensed exterminator. Places to look for rat infestations are around pipes, behind walls and near garbage cans. Effective rat control requires municipal workers and individuals to work together.

Rats as invasive species

When introduced into locations where rats previously did not exist they cause a huge amount of environmental degradation. Rattus rattus, the black rat, is considered to be one of the worlds worst invasive species.

As part of island restoration some islands have had their rat populations eradicated to protect or restore the ecology. Hawadax Island, Alaska was declared rat free after 229 years and Campbell Island, New Zealand after almost 200 years. Breaksea Island in New Zealand was declared rat free in 1988 after an eradication campaign based on a successful trial on the smaller Hawea Island nearby.

Culture

Ancient Romans did not generally differentiate between rats and mice, instead referring to the former as mus maximus (big mouse) and the latter as mus minimus (little mouse).

On the Isle of Man (a dependency of the British Crown), there is a taboo against the word " rat".

Asian cultures

The rat (sometimes referred to as a mouse) is the first of the twelve animals of the Chinese zodiac. People born in this year are expected to possess qualities associated with rats, including creativity, intelligence, honesty, generosity, ambition, a quick temper and wastefulness. 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 indigenous rats are allowed to run freely throughout the Karni Mata temple.

In Indian tradition, rats are seen as the vehicle of Ganesha, and a rat's statue is always found in a temple of Ganesh. In the northwestern Indian city of Deshnoke, the rats at the Karni Mata Temple are held to be destined for reincarnation as Sadhus ( Hindu holy men). The attending priests feed milk and grain to the rats, of which the pilgrims also partake.

European cultures

European associations with the rat are generally negative. For instance, "Rats!" is used as a substitute for various vulgar interjections in the English language. These associations do not draw, per se, from any biological or behavioural trait of the rat, but possibly from the association of rats (and fleas) with the 14th-century medieval plague called the Black Death. Rats are seen as vicious, unclean, parasitic animals that steal food and spread disease. However, some people in European cultures keep rats as pets and conversely find them to be tame, clean, intelligent, and playful.

Rats are often used in scientific experiments; animal rights activists allege the treatment of rats in this context is cruel. The term "lab rat" is used, typically in a self-effacing manner, to describe a person whose job function requires them to spend a majority of their work time engaged in bench-level research (such as postgraduate students in the sciences).

Terminology

Rats are frequently blamed for damaging food supplies and other goods, or spreading disease. Their reputation has carried into common parlance: in the English language, "rat" is often an insult or is generally used to signify an unscrupulous character; it is also used, as the term nark, to mean an individual who works as a police informant or who has turned state's evidence. Writer/director Preston Sturges created the humorous alias "Ratskywatsky" for a soldier who seduced, impregnated, and abandoned the heroine of his 1944 film, The Miracle of Morgan's Creek. It is a term ( noun and verb) in criminal slang for an informant - "to rat on someone" is to betray them by informing the authorities of a crime or misdeed they committed. Describing a person as "rat-like" usually implies he or she is unattractive and suspicious.

Among unions, "rat" is a term for nonunion employers or breakers of union contracts, and this is why unions use inflatable rats.

Judeo-Christianity

• In Leviticus 11:29, rats are prohibited as food.

Fiction

Imperial Japan was depicted as a rat in a World War II United States Navy propaganda poster.

Depictions of rats in fiction are historically inaccurate and negative. The most common falsehood is the squeaking almost always heard in otherwise realistic portrayals (i.e. non anthropomorphic). While the recordings may be of actual squeaking rats, the noise is uncommon - they may do so only if distressed, hurt, or annoyed. Normal vocalizations are very high-pitched, well outside the range of human hearing. Rats are also often cast in vicious and aggressive roles when in fact, their shyness helps keep them undiscovered for so long in an infested home.

The actual portrayals of rats vary from negative to positive with a majority in the negative and ambiguous. The rat plays a villain in several mouse societies; from Brian Jacques's Redwall and Robin Jarvis's The Deptford Mice, to the roles of Disney's Professor Ratigan and Kate DiCamillo's Roscuro and Botticelli. They have often been used as a mechanism in horror; being the titular evil in stories like The Rats or H.P. Lovecraft's The Rats in the Walls and in films like Willard and Ben. Another terrifying use of rats is as a method of torture, for instance in Room 101 in George Orwell's Nineteen Eighty-Four or The Pit and the Pendulum by Edgar Allan Poe.

Selfish helpfulness —those willing to help for a price— has also been attributed to fictional rats. Templeton, from E. B. White's Charlotte's Web, repeatedly reminds the other characters that he is only involved because it means more food for him, and the cellar-rat of John Masefield's The Midnight Folk requires bribery to be of any assistance.

By contrast, the rats appearing in the Doctor Dolittle books tend to be highly positive and likeable characters, many of whom tell their remarkable life stories in the Mouse and Rat Club established by the animal-loving doctor.

Some fictional works use rats as the main characters. Notable examples include the society created by O'Brien's Mrs. Frisby and the Rats of NIMH, Doctor Rat, Rizzo the Rat from The Muppets, and animated films such as Pixar's Ratatouille. Mon oncle d'Amérique ("My American Uncle"), a 1980 French film, illustrates Henri Laborit's theories on evolutionary psychology and human behaviors by using short sequences in the storyline showing lab rat experiments.

In Harry Turtledove's science fiction novel Homeward Bound, humans unintentionally introduce rats to the ecology at the home world of an alien race which previously invaded Earth and introduced some of its own fauna into its environment. And A. Bertram Chandler pitted his space-bound protagonist, Commodore Grimes, against giant, intelligent rats who took over several stellar systems and enslaved their human inhabitants. " The Stainless Steel Rat" is nickname of the (human) protagonist of a series of humorous science fiction novels written by Harry Harrison.

The Pied Piper

One of the oldest and most historic stories about rats is The Pied Piper of Hamelin, in which a rat-catcher leads away an infestation with enchanted music—the piper is later refused payment, so he in turn leads away the town's children. This tale, placed in Germany around the late 13th century, has inspired the realms of film, theatre, literature, and even opera. The subject of much research, some theories have intertwined the tale with events related to the Black Plague, in which black rats may have played an important role. Fictional works based on the tale that focus heavily on the rat aspect include Pratchett's The Amazing Maurice and his Educated Rodents, and Belgian graphic novel Le Bal du Rat Mort (The Ball of the Dead Rat).

Taxonomy of Rattus

The genus Rattus is a member of the giant subfamily Murinae. Several other murine genera are sometimes considered part of Rattus: 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 64 extant species. A subgeneric breakdown of the species has been proposed, but does not include all species.

Species