Plains viscacha rat
| Plains viscacha rat | |
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Yepes, 1942
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| Species: |
T. barrerae
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| Binomial name | |
| Tympanoctomys barrerae (B. Lawrence, 1941)[2]
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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]
The species is threatened by destruction of its fragmented and restricted habitat.[1]
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
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 closest living relation of T. barrerae 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.[citation needed]
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.[citation needed]
New data point to a hybrid nature of the T. barrerae karyotype, suggesting a hybridization event in the origin of this species.[12]
References
- ↑ 1.0 1.1 1.2 Lessa, E., Ojeda, R. & Bidau, C. (2008). Tympanoctomys barrerae. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 5 January 2009.
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