Plains viscacha rat
|Plains viscacha rat|
(B. Lawrence, 1941)
The plains viscacha rat or red vizcacha rat (Tympanoctomys barrerae) is a species of rodent in the family Octodontidae. The rodent is not a rat, but related to guinea pigs and chinchillas. It is monotypic within the genus Tympanoctomys. It is endemic to central western Argentina, where it has a fragmented range. Its natural habitat is desert scrubland, dunes and salt flats, where it eats halophyte plants. It is a solitary, nocturnal rodent that constructs large mounds with complex burrows.
This species of rodent is unusual because it is tetraploid (4x = 2n = 102). Scientists think that this species may 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). The doubling of its chromosome number was presumably by errors in mitosis or meiosis within the animal's reproductive organs.
Careful analysis using chromosome paints shows that there are only two copies of each chromosome in T. barrerae not the four expected if it were truly a tetraploid. Its "new" diploid [2n] number is (almost) double and so its cells are roughly twice normal size by virtue of having twice as many chromosomes instead of twice as many sets of chromosomes. Its closest living relation is Octomys mimax, the Andean Viscacha-Rat of the same family, whose 2n = 56. It was therefore surmised that an Octomys-like ancestor originally produced tetraploid (i.e., 2n = 4x = 112) offspring that were, by virtue of their doubled chromosomes, reproductively isolated from their parents, after loss of some chromosomes.
The golden vizcacha rat (Pipanacoctomys aureus) is also tetraploid and has 4x = 2n = 92 chromosomes. It is a sister-species to Tympanoctomys barrerae (4x = 102). In both cases the animals are by evolution developed from animals related to the diploid mountain vizcacha rat, Octomys mimax (2x = 2n = 56) as a result of doubling and then loss of some chromosomes.
New data point to a hybrid nature of the T. barrerae karyotype, suggesting a hybridization event in the origin of this species. Genome, 2012, 55(2): 105-117, 10.1139/g11-084
The species is threatened by destruction of its fragmented and restricted habitat.
- Lessa, E., Ojeda, R. & Bidau, C. (2008). Tympanoctomys barrerae. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 5 January 2009.
- Lawrence, B. (1941), "A new species of Octomys from Argentina", Proceedings of the New England Zoological Club 18: 43–46.
- Woods, C. A.; Kilpatrick, C. W. (2005). "Infraorder Hystricognathi". In Wilson, D. E.; Reeder, D. M. Mammal Species of the World (3rd ed.). Johns Hopkins University Press. p. 1573. ISBN 978-0-8018-8221-0. OCLC 62265494.
- Mares, Michael A. (1 November 2003), "Desert dreams: seeking the secret mammals of the salt pans - Naturalist at Large", Natural History
- Gallardo, M.H.; González, CA; Cebrián, I (2006), "Molecular cytogenetics and allotetraploidy in the red vizcacha rat, Tympanoctomys barrerae (Rodentia, Octodontidae)", Genomics (August 2006) 88 (2): 214–221, doi:10.1016/j.ygeno.2006.02.010, PMID 16580173, retrieved 2008-07-16
- Svartman M, Stone G, Stanyon R (Aprilt 2005). "Molecular cytogenetics discards polyploidy in mammals". Genomics 85 (4): 425–30. doi:10.1016/j.ygeno.2004.12.004. PMID 15780745.
- Mares, M. A.; Braun, J. K.; Barquez, R. M.; Díaz, M. M. 2000. Two new genera and species of halophytic desert mammals from isolated salt flats in Argentina. Occasional Papers, Museum of Texas Tech University 203:i+1-27.
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