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| Rats | |
|---|---|
.jpg) | |
| Brown rat (Rattus norvegicus) | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Mirorder: | Simplicidentata |
| Order: | Rodentia |
Rats are various medium-sized, long-tailedrodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genusRattus. Other rat genera includeNeotoma (pack rats),Bandicota (bandicoot rats) andDipodomys (kangaroo rats).
Rats are typically distinguished frommice by their size. Usually thecommon name of a largemuroid rodent will include the word "rat", while a smaller muroid's name will include "mouse". The common termsrat andmouse are nottaxonomically specific. There are 56 known species of rats in the world.[1]
The best-known ratspecies are theblack rat (Rattus rattus) and thebrown rat (Rattus norvegicus). This group, generally known as theOld World rats or true rats, originated inAsia. Rats are bigger than most Old Worldmice, which are their relatives, but seldom weigh over 500 grams (17+1⁄2 oz) in the wild.[2]
The termrat is also used in the names of other smallmammals that are not true rats. Examples include the North Americanpack rats (also known as wood rats[3]) and a number of species loosely calledkangaroo rats.[3] Rats such as thebandicoot rat (Bandicota bengalensis) aremurine rodents related to true rats but are not members of the genusRattus.[4][5]
Male rats are calledbucks; unmated females,does, pregnant or parent females,dams; and infants,kittens orpups. A group of rats is referred to as amischief.[6]
The common species are opportunistic survivors and often live with and nearhumans; therefore, they are known ascommensals. They may cause substantial food losses, especially in developing countries.[7] However, the widely distributed and problematic commensal species of rats are a minority in this diverse genus. Many species of rats areisland endemics, some of which have becomeendangered due to habitat loss or competition with the brown, black, orPolynesian rat.[8]
Wild rodents, including rats, can carry many differentzoonotic pathogens, such asLeptospira,Toxoplasma gondii, andCampylobacter.[9] TheBlack Death is traditionally believed to have been caused by the microorganismYersinia pestis, carried by thetropical rat flea (Xenopsylla cheopis), which preyed on black rats living in European cities during the epidemic outbreaks of theMiddle Ages; these rats were used as transport hosts. Another zoonotic disease linked to the rat isfoot-and-mouth disease.[10]
Rats become sexually mature at age 6 weeks, but reach social maturity at about 5 to 6 months of age. The average lifespan of rats varies by species, but many only live about a year due to predation.[11]
The black and brown rats diverged from otherOld World rats in the forests of Asia during the beginning of thePleistocene.[12]
The characteristic longtail of most rodents is a feature that has been extensively studied in various rat species models, which suggest three primary functions of this structure:thermoregulation,[13] minorproprioception, and anocifensive-mediateddegloving response.[14] Rodent tails—particularly in rat models—have been implicated with a thermoregulation function that follows from its anatomical construction. This particular tail morphology is evident across the family Muridae, in contrast to the bushier tails of Sciuridae, thesquirrel family. The tail is hairless and thin skinned but highly vascularized, thus allowing for efficientcountercurrent heat exchange with the environment. The highmuscular andconnective tissue densities of the tail, along with ample muscle attachment sites along its plentifulcaudal vertebrae, facilitate specific proprioceptive senses to help orient the rodent in a three-dimensional environment.[15] Murids have evolved a unique defense mechanism termeddegloving that allows for escape from predation through the loss of the outermostintegumentary layer on the tail. However, this mechanism is associated with multiplepathologies that have been the subject of investigation.[citation needed]
Multiple studies have explored the thermoregulatory capacity of rodent tails by subjecting test organisms to varying levels of physical activity and quantifyingheat conduction via the animals' tails. One study demonstrated a significant disparity inheat dissipation from a rat's tail relative to its abdomen.[16] This observation was attributed to the higher proportion ofvascularity in the tail, as well as its highersurface-area-to-volume ratio, which directly relates to heat's ability to dissipate via the skin. These findings were confirmed in a separate study analyzing the relationships of heat storage andmechanical efficiency in rodents that exercise in warm environments. In this study, the tail was a focal point in measuring heat accumulation and modulation.[citation needed]
On the other hand, the tail's ability to function as a proprioceptive sensor and modulator has also been investigated. As aforementioned, the tail demonstrates a high degree of muscularization and subsequentinnervation that ostensibly collaborate in orienting the organism.[17] Specifically, this is accomplished by coordinatedflexion and extension of tail muscles to produce slight shifts in the organism'scenter of mass, orientation, etc., which ultimately assists it with achieving a state of proprioceptive balance in its environment. Further mechanobiological investigations of the constituenttendons in the tail of the rat have identified multiple factors that influence how the organism navigates its environment with this structure. A particular example is that of a study in which the morphology of these tendons is explicated in detail.[18] Namely,cell viability tests of tendons of the rat's tail demonstrate a higher proportion of livingfibroblasts that produce thecollagen for these fibers. As in humans, these tendons contain a high density ofgolgi tendon organs that help the animal assess stretching of musclein situ and adjust accordingly by relaying the information to highercortical areas associated with balance, proprioception, and movement.[citation needed]
The characteristic tail of murids also displays a unique defense mechanism known asdegloving in which the outer layer of the integument can be detached in order to facilitate the animal's escape from a predator. This evolutionary selective pressure has persisted despite a multitude ofpathologies that can manifest uponshedding part of the tail and exposing more interior elements to the environment.[19] Paramount among these arebacterial andviral infection, as the high density ofvascular tissue within the tail becomes exposed uponavulsion or similar injury to the structure. The degloving response is a nocifensive response, meaning that it occurs when the animal is subjected to acutepain, such as when a predator snatches the organism by the tail.[citation needed]
Domesticated rats, selectively bred for specific traits, have been kept aspets since at least the late 19th century. Pet rats are most commonly domesticated variants of thebrown rat (Rattus norvegicus), though other species, such as theblack rat (Rattus rattus) and thegiant pouched rat (Cricetomys spp.), are also occasionally kept. Pet rats behave differently from their wild counterparts depending on how many generations they have been kept as pets.[20] Pet rats do not pose any more of a risk ofzoonotic diseases than pets such ascats ordogs.[21] Tamed rats are generally friendly and can be taught to perform selected behaviors.
Selective breeding has brought about different color and marking varieties in rats. Genetic mutations have also created different fur types, such as rex and hairless. Congenital malformation in selective breeding have created the dumbo rat, a popular pet choice due to their low, saucer-shaped ears.[22] A breeding standard exists for rat fanciers wishing to breed and show their rat at a rat show.[23]
In 1895,Clark University inWorcester, Massachusetts, established a population of domesticalbino brown rats to study the effects of diet and for otherphysiological studies.[citation needed] Over the years, rats have been used in many experimental studies, adding to our understanding ofgenetics,diseases, the effects ofdrugs, and other topics that have provided a great benefit for thehealth and wellbeing of humankind.[24]
Theaortic arches of the rat are among the most commonly studied in murine models due to markedanatomical homology to the humancardiovascular system.[25] Both rat and human aortic arches exhibit subsequent branching of thebrachiocephalic trunk, leftcommon carotid artery, and leftsubclavian artery, as well as geometrically similar, nonplanar curvature in theaortic branches.[25] Aortic arches studied in rats exhibit abnormalities similar to those of humans, including alteredpulmonary arteries and double or absent aortic arches.[26] Despite existing anatomical analogy in the inthrathoracic position of the heart itself, the murine model of the heart and its structures remains a valuable tool for studies of human cardiovascular conditions.[25]
The rat's larynx has been used in experimentations that involve inhalation toxicity, allograft rejection, and irradiation responses. One experiment described four features of the rat's larynx. The first being the location and attachments of the thyroarytenoid muscle, the alar cricoarytenoid muscle, and the superior cricoarytenoid muscle, the other of the newly named muscle that ran from the arytenoid to a midline tubercle on the cricoid. The newly named muscles were not seen in the human larynx. In addition, the location and configuration of the laryngeal alar cartilage was described. The second feature was that the way the newly named muscles appear to be familiar to those in the human larynx. The third feature was that a clear understanding of how MEPs are distributed in each of the laryngeal muscles was helpful in understanding the effects of botulinum toxin injection. The MEPs in the posterior cricoarytenoid muscle, lateral cricoarytenoid muscle, cricothyroid muscle, and superior cricoarytenoid muscle were focused mostly at the midbelly. In addition, the medial thyroarytenoid muscle were focused at the midbelly while the lateral thyroarytenoid muscle MEPs were focused at the anterior third of the belly. The fourth and final feature that was cleared up was how the MEPs were distributed in the thyroarytenoid muscle.[27]
Laboratory rats have also proved valuable in psychological studies of learning and other mental processes (Barnett 2002), as well as to understandgroup behavior and overcrowding (with the work ofJohn B. Calhoun onbehavioral sink).[28][29] A 2007 study found rats to possessmetacognition, a mental ability previously only documented in humans and someprimates.[30][31]
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 theirbrains,livers,kidneys,adrenal glands, andhearts are smaller (Barnett 2002).
Brown rats are often used asmodel organisms for scientific research. Since the publication of the ratgenome sequence,[32] and other advances, such as the creation of a ratSNP chip, and the production ofknockout rats, thelaboratory rat has become a useful genetic tool, although not as popular asmice. Entirely newbreeds or "lines" of brown rats, such as theWistar rat, have been bred for use in laboratories. Much of the genome ofRattus norvegicus has been sequenced.[33]
When it comes to conducting tests related tointelligence, learning, anddrug abuse, rats are a popular choice due to their high intelligence, ingenuity,aggressiveness, andadaptability. Theirpsychology seems in many ways similar to that of humans.[34] Inspired byB. F. Skinner's famous box which dispensed food pellets when rats pushed a lever, photographer Augustin Lignier gave two rats periodic, unpredictable rewards for pressing a button. He likened their repeated button-pressing behaviors to people's fascinations with digital and social media.[35]
Early studies found evidence both for and against measurable intelligence using the "g factor" in rats.[36][37] Part of the difficulty of understandinganimal cognition, generally, is determining what to measure.[38] One aspect of intelligence is the ability to learn, which can be measured using a maze like theT-maze.[38] Experiments done in the 1920s showed that some rats performed better than others in maze tests, and if these rats were selectively bred, their offspring also performed better, suggesting that in rats an ability to learn was heritable in some way.[38]
Rat meat is afood that, whiletaboo in some cultures, is a dietary staple in others.[39]
Rats have been used asworking animals. Tasks for working rats include the sniffing of gunpowder residue,demining, acting andanimal-assisted therapy. Rats have a keen sense of smell and are easy to train. These characteristics have been employed, for example, by the Belgiannon-governmental organizationAPOPO, which trains rats (specificallyAfrican giant pouched rats) to detectlandmines and diagnosetuberculosis through smell.[40]
Rats have long been considered deadlypests. Once considered a modern myth, therat flood inIndia occurs every 50 years, as armies ofbamboo rats descend upon rural areas and devour everything in their path.[41] Rats have long been held up as the chief villain in the spread of theBubonic Plague;[42] however, recent studies show that rats alone could not account for the rapid spread of the disease through Europe in theMiddle Ages.[43] Still, theCenters for Disease Control and Prevention does list nearly a dozen diseases directly linked to rats.[44]
Most urban areas battle rat infestations. A 2015 study by theAmerican Housing Survey (AHS) found that 18% of homes inPhiladelphia showed evidence of rodents.Boston,New York City, andWashington, D.C., also demonstrated significant rodent infestations.[45] Indeed,rats in New York City are famous for their size and prevalence. The urban legend that the rat population inManhattan equals that of its human population was definitively refuted by Robert Sullivan in his bookRats but illustrates New Yorkers' awareness of the presence, and on occasion boldness and cleverness, of the rodents.[46] New York has specific regulations for eradicating rats; multifamily residences and commercial businesses must use a specially trained and licensedrat-catcher.[47]
Chicago was declared the "rattiest city" in the U.S. by the pest control companyOrkin in 2020, for the sixth consecutive time. It is followed byLos Angeles, New York, Washington, D.C., andSan Francisco.[48] To help combat the problem, a Chicago animal shelter has placed more than 1000 feral cats (sterilized and vaccinated) outside of homes and businesses since 2012, where they hunt and catch rats while also providing a deterrent simply by their presence.[49]
Rats have the ability to swim upsewer pipes intotoilets.[50][51] Rats will infest any area that provides shelter and easy access to sources of food and water, including undersinks, neargarbage, and inside walls orcabinets.[52]
Rats can serve aszoonotic vectors for certain pathogens and thus spread disease, such asbubonic plague,Lassa fever,leptospirosis, andhantavirus infection.[53] Researchers studying New York City wastewater have also cited rats as the potential source of "cryptic"SARS-CoV-2 lineages, due to unknown viral RNA fragments in sewage matching mutations previously shown to make SARS-CoV-2 more adept at rodent-based transmission.[54]
Rats are also associated with humandermatitis because they are frequently infested with blood feeding rodent mites such as the tropical rat mite (Ornithonyssus bacoti) and spiny rat mite (Laelaps echidnina), which will opportunistically bite and feed on humans,[55] where the condition is known asrat mite dermatitis.[56]
When introduced into locations where rats previously did not exist, they can wreak an enormous degree ofenvironmental degradation.Rattus rattus, theblack rat, is considered to be one of the world's worst invasive species.[57] Also known as theship rat, it has been carried worldwide as astowaway onseagoing vessels for millennia and has usually accompanied men to any new area visited or settled by human beings by sea. Rats first got to countries such asAmerica andAustralia by stowing away on ships.[58] The similar speciesRattus norvegicus, thebrown rat orwharf rat, has also been carried worldwide by ships in recent centuries.[59]
The ship or wharf rat has contributed to the extinction of many species of wildlife, includingbirds, smallmammals,reptiles,invertebrates, andplants, especially onislands.True rats areomnivorous, capable of eating a wide range of plant and animal foods, and have a very highbirth rate. When introduced to a new area, they quickly reproduce to take advantage of the new food supply. In particular, they prey on the eggs and young of forest birds, which on isolated islands often have no other predators and thus haveno fear of predators.[60] Some experts believe that rats are to blame for between forty percent and sixty percent of all seabird and reptile extinctions, with ninety percent of those occurring on islands. Thus man has indirectly caused the extinction of many species by accidentally introducing rats to new areas.[61]
Rats are found in nearly all areas of Earth which are inhabited by human beings. The only rat-free continent isAntarctica, which is too cold for rat survival outdoors, and its lack of human habitation does not provide buildings to shelter them from the weather. However, rats have been introduced to many of the islands near Antarctica, and because of their destructive effect on native flora and fauna, efforts to eradicate them are ongoing. In particular,Bird Island (just off rat-infestedSouth Georgia Island), where breeding seabirds could be badly affected if rats were introduced, is subject to special measures and regularly monitored for rat invasions.[62]
In January 2015, an international "Rat Team" (organized by the South Georgia Heritage Trust) set sail from theFalkland Islands for theBritish Overseas Territory ofSouth Georgia and the South Sandwich Islands on board a ship carrying three helicopters and 100 tons of rat poison with the objective of "reclaiming the island for its seabirds". Rats had wiped out more than 90% of the seabirds on South Georgia, and the sponsors hoped that once the rats were gone, it would regain its former status as home to the greatest concentration of seabirds in the world.[63]
As part ofisland restoration, some islands' rat populations have been eradicated to protect or restore theecology.Hawadax Island, Alaska was declared rat free after 229 years[64] andCampbell Island, New Zealand after almost 200 years.[65][66]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.[67][68]
After an eradication programme,Lundy in England was declared free of brown and black rats in 2006, allowing a subsequent recovery of the island's seabirds.[69] In 2008, the Scottish island ofCanna was declared free of its 10,000 rat population after a three-year programme of baiting and trapping.[70]
The Canadian province ofAlberta is notable for being the largest inhabited area on Earth which is free of true rats due to very aggressive government rat control policies. It has large numbers of nativepack rats, also called bushy-tailed wood rats, but they are forest-dwelling vegetarians which are much less destructive than true rats.[71]
Alberta was settled by Europeans relatively late in North American history and only became a province in 1905. Black rats cannot survive in its climate at all, and brown rats must live near people and in their structures to survive the winters. There are numerous predators in Canada's vast natural areas which will eat non-native rats, so it took until 1950 for invading rats to make their way over land from Eastern Canada.[72] Immediately upon their arrival at the eastern border withSaskatchewan, the Alberta government implemented an extremely aggressive rat control program to stop them from advancing further. A systematic detection and eradication system was used throughout a control zone about 600 kilometres (400 mi) long and 30 kilometres (20 mi) wide along the eastern border[further explanation needed] to eliminate rat infestations before the rats could spread further into the province. Shotguns, bulldozers, high explosives, poison gas, and incendiaries were used to destroy rats. Numerous farm buildings were destroyed in the process. Initially, tons ofarsenic trioxide were spread around thousands of farm yards to poison rats, but soon after the program commenced therodenticide and medical drugwarfarin was introduced, which is much safer for people and more effective at killing rats than arsenic.[73]
Forceful government control measures, strong public support and enthusiastic citizen participation continue to keep rat infestations to a minimum.[74] The effectiveness has been aided by a similar but newer program in Saskatchewan which prevents rats from even reaching the Alberta border. Alberta still employs an armed rat patrol to control rats along Alberta's borders. About ten single rats are found and killed per year, and occasionally a large localized infestation has to be dug out with heavy machinery, but the number of permanent rat infestations is zero.[75]
Ancient Romans did not generally differentiate between rats and mice, instead referring to the former asmus maximus (big mouse) and the latter asmus minimus (little mouse).[76]
On theIsle of Man, there is ataboo against the word "rat".[77]
The rat (sometimes referred to as a mouse) is the first of the twelve animals of theChinese 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".
In Indian tradition, rats are seen as the vehicle ofGanesha, and a rat's statue is always found in a temple of Ganesh. In the northwestern Indian city ofDeshnoke, the rats at theKarni Mata Temple are held to be destined forreincarnation asSadhus (Hindu holy men). The attending priests feed milk and grain to the rats, of which the pilgrims also partake.
European associations with the rat are generally negative. For instance, "Rats!" is used as a substitute for various vulgarinterjections in the English language. These associations do not draw,per se, from any biological or behavioral trait of the rat, but possibly from the association of rats (andfleas) with the 14th-century medieval plague called theBlack Death. Rats are seen as vicious, unclean, parasitic animals that steal food and spread disease. In 1522, the rats inAutun, France were charged and put ontrial for destroying crops.[78] However, some people in European cultures keeprats as pets and conversely find them to be tame, clean, intelligent, and playful.
Rats are often used in scientificexperiments;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 aspostgraduate students in the sciences).
Rats are frequently blamed for damaging food supplies and other goods, or spreading disease. Their reputation has carried into common parlance: in theEnglish language, "rat" is often an insult or is generally used to signify an unscrupulous character; it is also used, as a synonym for the termnark, to mean an individual who works as a policeinformant or who has turnedstate's evidence. Writer/directorPreston 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 andverb) in criminal slang for an informant – "to rat on someone" is to betray them by informing the authorities of acrime or misdeed they committed. Describing a person as "rat-like" usually implies he or she is unattractive and suspicious.
Amongtrade unions, the word "rat" is also a term for nonunion employers or breakers of union contracts, and this is why unions useinflatable rats.[79]
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.nonanthropomorphic). 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.[80] The rat plays a villain in several mouse societies; from Brian Jacques'sRedwall and Robin Jarvis'sThe Deptford Mice, to the roles of Disney'sProfessor Ratigan and Kate DiCamillo'sRoscuro andBotticelli. They have often been used as a mechanism in horror; being the titular evil in stories likeJames Herbert'sThe Rats orH.P. Lovecraft's "The Rats in the Walls",[80] in films likeWillard andBen, or bothStephen King's "Graveyard Shift" and itsfilm adaptation.[81] Another terrifying use of rats is as a method oftorture, for instance inRoom 101 in George Orwell'sNineteen Eighty-Four orThe Pit and the Pendulum byEdgar Allan Poe.
Selfish helpfulness—those willing to help for a price—has also been attributed to fictional rats.[80] Templeton, from E. B. White'sCharlotte'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'sThe Midnight Folk requires bribery to be of any assistance.
By contrast, the rats appearing in theDoctor 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. InThe Underland Chronicles series, rats are both allies (such as Ripred)[82] and enemies (such as Bane,[83] and King Gorger).
Some fictional works use rats as the main characters. Notable examples include the society created by O'Brien'sMrs. Frisby and the Rats of NIMH, and others includeDoctor Rat, andRizzo the Rat fromThe Muppets.Pixar's 2007 animated filmRatatouille is about a rat described byRoger Ebert as "earnest... lovable, determined, [and] gifted" who lives with a Parisian garbage-boy-turned-chef.[84]
Mon oncle d'Amérique ("My American Uncle"), a 1980French film, illustratesHenri Laborit's theories onevolutionary psychology andhuman behaviors by using short sequences in the storyline showing lab rat experiments.
InHarry Turtledove's science fiction novelHomeward 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.A. Bertram Chandler pitted the space-bound protagonist of a long series of novels, 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 humorousscience fictionnovels written byHarry Harrison.
Wererats,therianthropic creatures able to take the shape of a rat,[85] have appeared in the fantasy or horror genre since the 1970s. The term is a neologism coined in analogy towerewolf.[citation needed] The concept has since become common inrole-playing games likeDungeons & Dragons[85][86][87] and fantasy fiction like theAnita Blake series.[88]
One of the oldest and most historic stories about rats is "The Pied Piper of Hamelin", in which arat-catcher leads away an infestation with enchanted music.[89] The piper is later refused payment, so he in turn leads away the town's children. This tale, traced toGermany around the late 13th century, has inspired adaptations in film, theatre, literature, and even opera. The subject of much research, some theories have intertwined the tale with events related to theBlack Plague, in whichblack rats played an important role. Fictional works based on the tale that focus heavily on the rat aspect include Pratchett'sThe Amazing Maurice and His Educated Rodents, and Belgian graphic novelLe Bal du Rat Mort [fr] (The Ball of the Dead Rat). Furthermore, a linguistic phenomenon when a wh-expression drags with it an entire encompassing phrase to the front of the clause has been namedpied-piping after "Pied Piper of Hamlin".[90]
Remy, the earnest little rat who is its hero, is such a lovable, determined, gifted rodent that I want to know what happens to him next, now that he has conquered the summit of French cuisine.
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