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 (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

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, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

. 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: ''Tympanoctomys barrerae, T. barrerae'', ''Tympanoctomys kirchnerorum, T. kirchnerorum'' and ''Tympanoctomys loschalchalerosorum, T. l ...

''.

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 only 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 foun ...

to central western

, where it has a fragmented range in

Mendoza Province Mendoza (), officially the 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 r ...

and western La Pampa. 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 a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite. Nocturnal creatur ...

. 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. ...

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 ...

'' and '' Suaeda'', 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

This species of rodent has (as of 2023) the third highest number of chromosomes of any known mammal (2n = 102), behind the tree pangolin (2n = 113/114) and the Bolivian bamboo rat (2n = 118). It was described as the first known

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

( 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 package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most import ...

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 Mitosis () is a part of the cell cycle in eukaryote, eukaryotic cells in which replicated chromosomes are separated into two new Cell nucleus, nuclei. Cell division by mitosis is an equational division which gives rise to genetically identic ...

meiosis Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...

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; : spermatozoa; ) is a motile sperm cell (biology), cell produced by male animals relying on internal fertilization. A spermatozoon is a moving form of the ploidy, haploid cell (biology), cell that is ...

are roughly twice normal size, thought to be by virtue of having twice as many sets of chromosomes.

References

{{Taxonbar, from=Q1567530 Tympanoctomys Mammals of Argentina Mammals described in 1941 Endemic rodentia species of Argentina Taxonomy articles created by Polbot Taxa named by Barbara Lawrence (zoologist)