Plains viscacha rat

Plains viscacha rat
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Octodontidae
Genus: Tympanoctomys
Yepes, 1942
Species: T. barrerae
Binomial name
Tympanoctomys barrerae
(B. Lawrence, 1941)[2]

The plains viscacha rat or red vizcacha rat (Tympanoctomys barrerae) is a species of rodent in the family Octodontidae native to Argentina. It is one of two species in the genus Tympanoctomys.[3][4]

Description

The plains viscacha rat is a moderately-sized rat, with a large head, long tail, and short ears. Adults measure about 13 cm (5.1 in) in total length, with a 15 cm (5.9 in) tail, and weigh an average of 90 g (3.2 oz), 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.[5]

Distribution and habitat

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 300 and 1,400 m (980 and 4,590 ft). There are no recognised subspecies.[1][5]

Biology and behaviour

Plains viscacha rats are solitary, and nocturnal. They construct complex burrow systems within large artificial mounds.[6] Typical mounds are 13.6 by 8.7 m (45 by 29 ft) across, and 1.25 m (4 ft 1 in) 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.[5]

The rats are herbivorous, feeding primarily on halophytic vegetation, such as Atriplex and Suaeda,[7] although they will occasionally eat other plants such as grass.[5] The rats scrape salt from the leaves of Atriplex saltbushes with their teeth and bristles around their mouths before eating them.[8] Although this reduces their salt intake, they still produce highly concentrated urine to help maintain their water balance.[9]

The young are born blind, and weighing about 4 g (0.14 oz). Their eyes open at about six days, and they begin to take solid food at ten days.[5]

Genetics

Plains viscacha rat chromosomes

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.[10] The animal's spermatozoa are roughly twice normal size by virtue of having twice as many sets of chromosomes.[11]

The finding of tetraploidy in this species has, however, been controversial. One study found that there are only two copies of each chromosome in T. barrerae not the four expected if it were truly a tetraploid.[12] This has, however, been contradicted by subsequent work.[10]

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 evolved 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.[13]

The species is threatened by destruction of its fragmented and restricted habitat.[1]

References

  1. 1 2 3 Lessa, E., Ojeda, R. & Bidau, C. (2008). Tympanoctomys barrerae. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 5 January 2009.
  2. ↑ Lawrence, B. (1941), "A new species of Octomys from Argentina", Proceedings of the New England Zoological Club 18: 43–46
  3. ↑ Woods, C.A.; Kilpatrick, C.W. (2005). "Infraorder Hystricognathi". In Wilson, D.E.; Reeder, D.M. Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. p. 1573. ISBN 978-0-8018-8221-0. OCLC 62265494.
  4. ↑ Pablo Teta, Ulyses F. J. Pardiñas, Daniel E. Udrizar Sauthier i Milton H. Gallardo (2014), "A new species of the tetraploid vizcacha rat Tympanoctomys (Caviomorpha, Octodontidae) from central Patagonia, Argentina", Journal of Mammalogy 95 (1): 60–71, doi:10.1644/13-MAMM-A-160
  5. 1 2 3 4 5 Diaz, G.B.; et al. (2000). "Tympanoctomys barrerae" (PDF). Mammalian Species 646: 1–4. doi:10.1644/1545-1410(2000)646<1:tb>2.0.co;2.
  6. ↑ Mares, Michael A. (1 November 2003). "Desert dreams: seeking the secret mammals of the salt pans - Naturalist at Large" (PDF). Natural History: 29–34.
  7. ↑ Torres-Mura, J.C. (1989). "Herbivorous specialization of the South American desert rodent Tympanoctomys barrerae". Journal of Mammalogy 70 (3): 646–648. doi:10.2307/1381442.
  8. ↑ Mares, M.A.; et al. (1997). "How desert rodents overcome halophytic plant defenses". BioScience 47 (11): 699–704. doi:10.2307/1313210.
  9. ↑ Diaz, G.B. & Ojeda R.A. (1999). "Kidney structure and allometry of Argentine desert rodents". Journal of Arid Environments 41 (4): 453–461. doi:10.1006/jare.1998.0472.
  10. 1 2 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), pp. 214–221, doi:10.1016/j.ygeno.2006.02.010, PMID 16580173
  11. ↑ Gallardo, M.H.; et al. (1999). "Discovery of tetraploidy in a mammal". Nature 401 (6751): 341. doi:10.1038/43815.
  12. ↑ Svartman M, Stone G, Stanyon R; Stone; Stanyon (April 2005). "Molecular cytogenetics discards polyploidy in mammals". Genomics 85 (4): 425–30. doi:10.1016/j.ygeno.2004.12.004. PMID 15780745.
  13. ↑ Suárez-Villota, E. Y.; Vargas, R. A.; Marchant, C. L.; Torres, J. E.; Köhler, N.; Núñez, J. J.; de la Fuente, R.; Page, J.; et al. (2012). "Distribution of repetitive DNAs and the hybrid origin of the red vizcacha rat (Octodontidae)". Genome 55 (2): 105–117. doi:10.1139/g11-084. PMID 22272977.
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