The plains viscacha rat, plains vizcacha rat, red viscacha rat, or red vizcacha rat (''Tympanoctomys barrerae'') is a species of

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are na ...

in the family

Octodontidae Octodontidae is a family of rodents, restricted to southwestern South America. Fourteen species of octodontid are recognised, arranged in seven genera. The best known species is the common degu, ''Octodon degus''. Octodontids are medium-sized ...

native to

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

. It is one of three species in the genus ''

Tympanoctomys ''Tympanoctomys'' is a genus of rodent in the family Octodontidae. There are three extant species in the genus: '' T. barrerae'', '' T. kirchnerorum'' and '' T. loschalchalerosorum''. ''T. loschalchalerosorum'' was formerly considered to be monot ...

''.

Description

The plains viscacha rat is a moderately-sized rat, with a large head, long tail, and short ears. Adults measure about in total length, with a tail, and weigh an average of , with males being slightly larger than females. The rat has buff-yellow fur with white underparts, fading to dark brown at the tip of the tail.

Distribution and habitat

The plains viscacha rat is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

to central western

, where it has a fragmented range in

Mendoza Province Mendoza, officially Province of Mendoza, is a province of Argentina, in the western central part of the country in the Cuyo region. It borders San Juan to the north, La Pampa and Neuquén to the south, San Luis to the east, and the republic o ...

and western

La Pampa La Pampa () is a sparsely populated province of Argentina, located in the Pampas in the center of the country. Neighboring provinces are from the north clockwise San Luis, Córdoba, Buenos Aires, Río Negro, Neuquén and Mendoza. History I ...

. Its natural habitat is desert scrubland, dunes and salt flats, between . There are no recognised subspecies. The species is threatened by destruction of its fragmented and restricted habitat.

Biology and behaviour

Plains viscacha rats are solitary, and

nocturnal Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite. Nocturnal creatures generally have highly developed sens ...

. They construct complex burrow systems within large artificial mounds. Typical mounds are across, and in height, and have an average of 23 burrow entrances. Within the mound, the burrow system has up to three levels and contains numerous chambers and dead-end tunnels. The rats are herbivorous, feeding primarily on

halophytic A halophyte is a salt-tolerant plant that grows in soil or waters of high salinity, coming into contact with saline water through its roots or by salt spray, such as in saline semi-deserts, mangrove swamps, marshes and sloughs and seashores. T ...

vegetation, such as ''

Atriplex ''Atriplex'' () is a plant genus of about 250 species, known by the common names of saltbush and orache (; also spelled orach). It belongs to the subfamily Chenopodioideae of the family Amaranthaceae ''s.l.''. The genus is quite variable and w ...

'' and ''

Suaeda __NOTOC__ ''Suaeda'' is a genus of plants also known as seepweeds and sea-blites. Most species are confined to saline or alkaline soil habitats, such as coastal salt-flats and tidal wetlands. Many species have thick, succulent leaves, a character ...

'', although they will occasionally eat other plants such as grass. The rats scrape off and discard salt from the leaves of ''Atriplex'' saltbushes with their teeth and bristles around their mouths before eating them. Although this reduces their salt intake, they still produce highly concentrated urine to help maintain their water balance. The young are born blind, and weighing about . Their eyes open at about six days, and they begin to take solid food at ten days.

Genetics

Metaphase spread of the Viscacha rat (Tympanoctomys barrerae)

This species of rodent has (as of 2017) the largest number of chromosomes of any known mammal, 2n = 102. It was described as the first known

tetraploid Polyploidy is a condition in which the cells of an organism have more than one pair of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set contains ...

( 4x = 2n) mammal, thought to have arisen by hybridization and chromosome doubling from an ancestor (very possibly closely related to the mountain vizcacha rat, ''Octomys mimax'',

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

count 2x = 2n = 56). Some later studies have cast doubt on its tetraploid nature, while others have reasserted it. The doubling of its chromosome number was presumably by errors in

mitosis In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is mainta ...

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...

within the animal's reproductive organs. A comparison of the chromosomes of the plains viscacha rat and the mountain viscacha rat suggested that the chromosomes of the plains viscacha rat increased relatively rapidly (in evolutionary terms) due to a diverse set of highly repetitive elements. The animal's

spermatozoa A spermatozoon (; also spelled spermatozoön; ; ) is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote. (A zygote is a single cell, with a complete set of chromosomes, ...

are roughly twice normal size, thought to be by virtue of having twice as many sets of chromosomes. The rodent is not a

rat Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include ''Neotoma'' ( pack rats), ''Bandicota'' (bandicoot ...

, but a

caviomorph Caviomorpha is the rodent infraorder or parvorder that unites all New World hystricognaths. It is supported by both fossil and molecular evidence. The Caviomorpha was for a time considered to be a separate order outside the Rodentia, but is now a ...

, kin to

guinea pig The guinea pig or domestic guinea pig (''Cavia porcellus''), also known as the cavy or domestic cavy (), is a species of rodent belonging to the genus ''Cavia'' in the family Caviidae. Breeders tend to use the word ''cavy'' to describe the ani ...

s and

chinchilla Chinchillas are either of two species (''Chinchilla chinchilla'' and ''Chinchilla lanigera'') of crepuscular rodents of the parvorder Caviomorpha. They are slightly larger and more robust than ground squirrels, and are native to the Andes mount ...

References

{{Taxonbar, from=Q1567530 Tympanoctomys Mammals of Argentina Mammals described in 1941 Endemic fauna of Argentina Taxonomy articles created by Polbot