Plains viscacha rat

The plains viscacha rat is a moderately-sized rat, with a large head, long tail, and short ears. Adults measure about {{convert|13|cm|abbr=on}} in total length, with a {{convert|15|cm|abbr=on}} tail, and weigh an average of {{convert|90|g|abbr=on}}, 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.{{cite journal | author = Diaz, G.B. | date = 2000 | title = Tympanoctomys barrerae | journal = Mammalian Species | url = http://www.science.smith.edu/msi/pdf/646_Tympanoctomys_barrerae.pdf | pages = 1–4 | doi = 10.1644/1545-1410(2000)646<1:tb>2.0.co;2 | display-authors = etal | volume = 646 | access-date = 2015-07-11 | archive-url = https://web.archive.org/web/20160304054123/http://www.science.smith.edu/msi/pdf/646_Tympanoctomys_barrerae.pdf | archive-date = 2016-03-04 | url-status = dead }}

The plains viscacha rat is endemic to central western Argentina, where it has a fragmented range in Mendoza Province and western La Pampa. Its natural habitat is desert scrubland, dunes and salt flats, between {{convert|300|and|1400|m|abbr=on}}. There are no recognised subspecies.

The species is threatened by destruction of its fragmented and restricted habitat.

Plains viscacha rats are solitary, and nocturnal. They construct complex burrow systems within large artificial mounds.{{Cite journal

| last = Mares | first = Michael A.

| title = Desert dreams: seeking the secret mammals of the salt pans - Naturalist at Large

| journal = Natural History | pages = 29–34

| date = 1 November 2003 | url = http://digitallibrary.amnh.org/dspace/bitstream/handle/2246/6509/NH112n09b.pdf}} Typical mounds are {{convert|13.6|by|8.7|m|abbr=on}} across, and {{convert|1.25|m|abbr=on}} 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 vegetation, such as Atriplex and Suaeda,{{cite journal | author = Torres-Mura, J.C. | date = 1989 | title = Herbivorous specialization of the South American desert rodent Tympanoctomys barrerae | journal = Journal of Mammalogy | volume = 70 | issue = 3 | pages = 646–648 | doi = 10.2307/1381442| jstor = 1381442 }} 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.{{cite journal | author = Mares, M.A.| date = 1997 | title = How desert rodents overcome halophytic plant defenses | journal = BioScience | volume = 47 | issue = 11 | pages = 699–704 | doi = 10.2307/1313210 |display-authors=etal| jstor = 1313210 | doi-access = }} Although this reduces their salt intake, they still produce highly concentrated urine to help maintain their water balance.{{cite journal |author1=Diaz, G.B. |author2=Ojeda R.A. |name-list-style=amp | date = 1999 | title = Kidney structure and allometry of Argentine desert rodents | journal = Journal of Arid Environments | volume = 41 | issue = 4 | pages = 453–461 | doi = 10.1006/jare.1998.0472|bibcode=1999JArEn..41..453D }}

The young are born blind, and weighing about {{convert|4|g|abbr=on}}. Their eyes open at about six days, and they begin to take solid food at ten days.

File:Metaphase spread of the Viscacha rat (Tympanoctomys barrerae).jpg

This species of rodent has (as of 2023) the third highest number of chromosomes of any known mammal (2n = 102),{{Cite journal|last1=Evans|first1=Ben J.|last2=Upham|first2=Nathan S.|last3=Golding|first3=Brian G.|last4=Ojeda|first4=Ricardo A.|last5=Ojeda|first5=Agustina A.|title=Evolution of the largest mammalian genome|journal=Genome Biology and Evolution|volume=9|issue=6|pages=1711–1724|doi=10.1093/gbe/evx113|year=2017|pmc=5569995|pmid=28854639}} behind the tree pangolin (2n = 113/114){{Cite journal |last=Houck |first=Marlys L. |last2=Koepfli |first2=Klaus-Peter |last3=Hains |first3=Taylor |last4=Khan |first4=Ruqayya |last5=Charter |first5=Suellen J. |last6=Fronczek |first6=Julie A. |last7=Misuraca |first7=Ann C. |last8=Kliver |first8=Sergei |last9=Perelman |first9=Polina L. |last10=Beklemisheva |first10=Violetta |last11=Graphodatsky |first11=Alexander |last12=Luo |first12=Shu-Jin |last13=O’Brien |first13=Stephen J. |last14=Lim |first14=Norman T.-L. |last15=Chin |first15=Jason S. C. |date=2023-04-12 |title=Chromosome-length genome assemblies and cytogenomic analyses of pangolins reveal remarkable chromosome counts and plasticity |url=https://doi.org/10.1007/s10577-023-09722-y |journal=Chromosome Research |language=en |volume=31 |issue=2 |pages=13 |doi=10.1007/s10577-023-09722-y |issn=1573-6849|url-access=subscription }} and the Bolivian bamboo rat (2n = 118).{{Cite journal |last=Dunnam |first=J. L. |last2=Salazar-Bravo |first2=J. |last3=Yates |first3=T. L. |date=2001 |title=The Bolivian Bamboo Rat, Dactylomys boliviensis (Rodentia: Echimyidae), a new record for chromosome number in a mammal. |url=https://www.researchgate.net/publication/259930848_The_Bolivian_Bamboo_Rat_Dactylomys_boliviensis_Rodentia_Echimyidae_a_new_record_for_chromosome_number_in_a_mammal |journal=Mammalian Biology |volume=66 |issue=2 |pages=121-126 |via=Springer}}

It was described as the first known tetraploid (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 count 2x = 2n = 56). Some later studies have cast doubt on its tetraploid nature,{{cite journal|last2=Stone|first2=Gary|last3=Stanyon|first3=Roscoe|year=2005|title=Molecular cytogenetics discards polyploidy in mammals|journal=Genomics|volume=85|issue=4|pages=425–30|doi=10.1016/j.ygeno.2004.12.004|pmid=15780745|last1=Svartman|first1=Marta}}{{cite journal |last1=Graphodatsky |first1=Alexander S. |last2=Trifonov |first2=Vladimir A. |last3=Stanyon |first3=Roscoe |title=The genome diversity and karyotype evolution of mammals |journal=Molecular Cytogenetics |date=12 October 2011 |volume=4 |issue=1 |pages=22 |doi=10.1186/1755-8166-4-22|doi-access=free |pmc=3204295 }} while others have reasserted it.{{Citation | last1 = Gallardo | first1 = M.H. | publication-date = August 2006 | title = Molecular cytogenetics and allotetraploidy in the red vizcacha rat, Tympanoctomys barrerae (Rodentia, Octodontidae) | periodical = Genomics | volume = 88 | issue = 2 | pages = 214–221 | doi = 10.1016/j.ygeno.2006.02.010 | year = 2006 | pmid = 16580173 | last2 = González | first2 = CA | last3 = Cebrián | first3 = I| doi-access = free }} The doubling of its chromosome number was presumably by errors in mitosis or meiosis 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.{{Cite news|url=https://phys.org/news/2017-07-analysis-rare-argentinian-rat-largest.html|title=New analysis of rare Argentinian rat unlocks origin of the largest mammalian genome|date=2017-07-12|work=PhysOrg|access-date=2017-07-17}} The animal's spermatozoa are roughly twice normal size, thought to be by virtue of having twice as many sets of chromosomes.{{cite journal | author = Gallardo, M.H.| date = 1999 | title = Discovery of tetraploidy in a mammal | journal = Nature | volume = 401 | issue = 6751 | pages = 341 | doi = 10.1038/43815|display-authors=etal | pmid=10517628| bibcode = 1999Natur.401..341G | s2cid = 1808633 | doi-access = free }}

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{{Wikispecies|Tympanoctomys barrerae}}

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Category:Tympanoctomys

Category:Mammals of Argentina

Category:Mammals described in 1941

Category:Endemic rodentia species of Argentina

Category:Taxonomy articles created by Polbot

Category:Taxa named by Barbara Lawrence (zoologist)