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?Rats
Fossil range: Early Pleistocene - Recent
Black Rat (Rattus rattus)
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.

Rats are various medium sized rodents. "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, R. norvegicus. Many members of other rodent genera and families are also called rats and share many characteristics with true rats.

Rats are distinguished from mice by their size; rats generally have bodies longer than 12 cm (5 inches). Squirrels of most species are about the same size as rats but are members of their own family, Sciuridae, and are usually more specialized than rats.

The RatEdit

The best-known rat species are the Black Rat Rattus rattus and the Brown Rat R. norvegicus. The group is generally known as the Old World rats or true rats, and originated in Asia. Rats are bigger than most of their relatives, the Old World mice, but seldom weigh over 500 grams (1 lb) in the wild.

In Western countries, many people keep domesticated rats as pets. These are of the species R. norvegicus, which originated in the grasslands of China and spread to Europe and eventually, in 1775, to the New World. Pet rats are Brown Rats descended from those bred for research, and are often called "fancy rats", but they are still 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.

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 Xenopsylla cheopis which preyed on R. rattus living in European cities of the day; it is notable that these rats were victims of the plague themselves. It has recently been suggested that neither rats nor infected fleas would have spread fast enough through Europe to be a likely culprit, although this is controversial and research continues.[How to reference and link to summary or text] 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 to the authorities a crime or misdeed they committed. 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.[How to reference and link to summary or text] 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 and mites, but do not generally spread disease to humans.

Rats have a normal lifespan ranging from two to five years, though three years is typical.

Rats as vermin Edit

Rattus norvegicus 1

Brown Rat (Rattus norvegicus)

By most standards, rats are considered pests or vermin. They can be very destructive to crops and property. Rats can quickly overpopulate when they live in a place where they have no predators, such as in certain cities, and their numbers can become hard to contain. Because of this, the entire province of Alberta, Canada has upheld and maintained a rat-free status since the early 1950s[1]; it is even illegal to keep pet rats there.

Rats have a significant impact on food production. Estimates vary, but it is likely that about one-fifth of the world's total food output is eaten, spoiled or destroyed by rats. [2] It is interesting to note that about one-third of the food purchased by humans is thrown away as garbage in certain areas. [3]

Rats can carry over thirty different diseases dangerous to humans, including Weil's disease, typhus, salmonella and bubonic plague. Black rats are suspected to have had a role in the Black Death, an epidemic which killed at least 75 million people in Europe, the Middle East, and Asia in the mid-late 14th century.

A variety of rat control methods have been used throughout human history to either reduce or eliminate rat populations in homes, markets, farms, and industrial sites. The two most widely used methods are rat poison and rat traps, though cats and dogs have also been employed to hunt rats. Professional rat-catchers can be found in many developing countries.

Because rats are nocturnal, daytime sightings of rat activity can mean that their nesting areas have been disturbed or, more likely, that there is overpopulation of them in the local area. [4] It is typically at this point that vermin control measures tend to increase.

Rats often chew electrical cables. Around 26% of all electrical cable breaks are caused by rats, and around 18% of all phone cable breaks. Around 25% of all fires of unknown origin are estimated to be caused by rats.[5]

Rats, particularly roof rats (Rattus rattus), can enter the attics of homes where they mate and nest. This problem occurs commonly in coastal, temperate climates and affects even the cleanest, well-kept homes.

Rats as subjects of scientific researchEdit

Main article: Brown rat#Brown rats in science
Rat diabetic

A domesticated rat, suffering from Diabetes mellitus a metabolic disorder being also a common disease among humans.

In 1895, Clark University in Worcester, Massachusetts (United States) established a population of domestic white 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 wellbeing of humankind. Laboratory rats have also proved valuable in psychological studies of learning and other mental processes (Barnett 2002). A 2007 study found rats to possess metacognition, a mental ability previously only found in humans and some primates.[1]

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 model organisms for scientific research. When conducting genetic research rats are much rarer than mice. When it comes to conducting tests related to intelligence, learning and drug abuse rats are a popular choice since 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 like the Wistar rat have been bred for use in laboratories. Much of the genome of Rattus norvegicus has been sequenced.[2]

Rat learning Edit

Laughter in ratsEdit

It was discovered that rats emit short, high frequency, ultrasonic, socially induced vocalization during rough and tumble play, and when tickled. The vocalization is described as a distinct “chirping”. Humans cannot hear the “chirping” without special equipment. It was also discovered that like humans, rats have “tickle skin”. These are certain areas of the body which generate more laughter response than other areas. The laughter is associated with positive emotional feelings and social bonding occurs with the human tickler, resulting in the rats becoming conditioned to seek the tickling. Additional responses to the tickling were those that laughed the most also played the most, and those that laughed the most preferred to spend more time with other laughing rats. This suggests a social preference to other rats exhibiting similar responses. However, as the rats age, there does appear to be a decline in the tendency to laugh and respond to tickle skin. The initial goal of Jaak Panksepp & Jeff Burgdorf’s research was to track the biological origins of joyful and social processes of the brain by comparing rats and their relationship to the joy and laughter commonly experienced by children in social play. Although, the research was unable to prove rats have a sense of humor, it did indicate rats can laugh and express joy. Panksepp & Burgdorf 2003 Chirping by rats is also reported in additional studies by Brian Knutson of the National Institutes of Health. Rats chirp when wrestling one another, before receiving morphine, or having sex. The sound has been interpreted as an expectation of something rewarding. Science News 2001

Rats as foodEdit

Rats, like all mammals, are edible by humans and are sometimes captured and eaten in emergency situations. Bandicoot rats are an important food source among some peoples in India and Southeast Asia. Among the reasons rat meat is not more widely utilized are the strong prohibitions against it in Islamic and Jewish dietary laws, the prohibition of all meat in Hinduism, and the rat's bad reputation in many cultures.

Taxonomy of RattusEdit

The genus Rattus is a member of the giant subfamily Murinae. There are several other murine genera that 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 56 species. A subgeneric breakdown of the species has been proposed, but does not include all species. The five groups are:

  • norvegicus group
  • rattus group
  • Australian native rat species
  • New Guinea native rat species
  • xanthurus group

The following list is alphabetical.

Species of ratsEdit

Further reading Edit

  • The Story of Rats: Their Impact on Us, and Our Impact on Them, S. Anthony Barnett, Allen & Unwin, Crows Nest, NSW, Australia, 2002, trade paperback, 202 pages, ISBN 1-86508-519-7 .
  • Jahn, G. C., P. Cox, S. Mak, and N. Chhorn 1999. Farmer participatory research on rat management in Cambodia. In G. Singleton, L. Hinds, H. Leirs and Zhibin Zhang [Eds.] “Ecologically-based rodent management” ACIAR, Canberra. Ch. 17, pp. 358-371. ISBN: 1 86320 262 5
  • Leung LKP, Peter G. Cox, G. C. Jahn and Robert Nugent. 2002. Evaluating rodent management with Cambodian rice farmers. Cambodian Journal of Agriculture Vol. 5, pp. 21-26.
  • Musser, G. G. and M. D. Carleton. 1993. Family Muridae. Pp. 501-755 in Mammal Species of the World a Taxonomic and Geographic Reference. D. E. Wilson and D. M. Reeder eds. Smithsonian Institution Press, Washington D.C.
  • Nowak, R. M. 1999. Walker's Mammals of the World, Vol. 2. Johns Hopkins University Press, London.
  • Sullivan, Robert. 2004. Rats - A Year with New York´s Most Unwanted Inhabitants. Granta Books, London.
  • Sullivan, Robert. 2005. Rats: Observations on the History and Habitat of the City's Most Unwanted Inhabitants. Bloomsbury USA. ISBN 1-58234-477-9

References and notesEdit

  1. | Rats Capable Of Reflecting On Mental Processes
  2. Genome project. www.ensemble.org. URL accessed on 2007-02-17.

See alsoEdit


External linksEdit

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