Red vizcacha rat skulls been reported in barn owl (Tyto alba) pellets. Although little information is available concerning the depredation of red vizcacha rats, other potential predators may include snakes (Bothrops newiedii, Bothrops ammodytoides), owls (Bubo virginianus, Genus: Athenecunicularia), mustelids (Lyncodon patagonieus, Galictis cuja), pampas cats (Lynchailurus pajeros), and pampas foxes (Lycalopex gymnocercus; Diaz and Ojeda, 2000).
Known Predators:
Tympanoctomys barrerae has a relatively large head. Cranial width is greater than the cranial length due to highly developed auditory bullae, which extend posteriorly beyond the braincase. Its ears are short with terminal pale hair tufts. Dorsal pelage is buffy-yellow and ventral pelage is white. Its hind feet are relatively short and are covered in long white hair. Its long, bicolored tail makes up 49 to 54% of its total length and is covered with long hair that becomes dark to reddish brown near the tip (Diaz and Ojeda, 2000; Grzimek, 2004). It can be distinguished from similar species, such as Octomys mimax, by its short hind feet, long tail, and shorter skull. Tympanoctomys barrerae has well-developed tympanic bones, short and rounded nasals, and a short maxillary tooth row (Diaz and Ojeda, 2000). It ranges in mass from 51.8 to 104 g and males tend to be larger than females. Finally, T. barrerae has a basal metabolic rate ranging from 0.9 to 1.25 cm^3 oxygen/hour.
Range mass: 51.8 to 104 g.
Range basal metabolic rate: .9 to 1.25 cm3.O2/g/hr.
Sexual Dimorphism: male larger
Other Physical Features: endothermic ; bilateral symmetry
Little information exists regarding lifespan or longevity in red vizcacha rats.
Tympanoctomys barrerae inhabits the Monte and Patagonia deserts, where it burrows in arid, lowland, sand dune vegetation belts along the periphery of saline lakes (Torres et al., 2003; Ojeda, 2010). The salt content of in these lakes is very high, resulting in a local abundance of halophytic vegetation. High burrow activity has been noted in vegetation belts surrounding these lakes where salt content is much higher (Mares et al., 1997). It is important to note that T. barrerae occurs in low population densities throughout these habitats (Ojeda, 2010).
Range elevation: 300 to 1,400 m.
Habitat Regions: terrestrial
Terrestrial Biomes: desert or dune
Tympanoctomys barrerae is the first known tetraploid mammal (2n=102). Larger cell dimensions are expected in polyploid species, and spermatozoa, liver cells, lymphocytes, and female reproductive cells are larger in T. barrerae than in most other rodent species (Diaz and Ojeda, 2000; Gallardo et al. 2002; Gallardo et al., 2006).
Little information is available on communication and perception in red vizcacha rats. However, based on their enlarged auditory bullae, they likely rely heavily on auditory signals.
Perception Channels: visual ; tactile ; acoustic ; chemical
Tympanoctomys barrerae may be a keystone species for xeric halophytic shrublands surrounding salt basins (Mares et al., 1997). Due to its patchy and restricted distribution, habitat and dietary specialization, low colonization rates, and low population densities, its populations are vulnerable to decline and should be considered in biodiversity assessments (Diaz and Ojeda, 2000). Fossil remains imply that the present distribution of T. barrerae was at one point more continuous and widespread (Gallardo et al., 2006). The IUCN Red List of Threatened Species lists T. barrerae as "near threatened" and suggests that the expansion of petroleum industry throughout South America is a threat to its persistence.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: near threatened
There are no known adverse effects of Tympanoctomys barrerae on humans.
There are no known positive effects of Tympanoctomys barrerae on humans.
Tympanoctomys barrerae greatly modify the ecosystem they occur in. Burrows provide ideal microhabitats for desert shrubs, which are more abundant on active burrows than between them (Mares et al., 1997). Atriplex species are especially prominent on burrow structures, providing T. barrerae with shelter and a convenient, primary food source (Mares, Braun and Channell, 1997). Burrows also provide habitat for other animals, including some species of arachnids (e.g., spiders and scorpions) and other species of rodent (Genus: Eligmodontia). Tympanoctomys barrerae is also host to a number of different parasites including fleas (Siphonaptera) and chigger fleas (Hectopsylla).
Ecosystem Impact: creates habitat; soil aeration
Commensal/Parasitic Species:
Red vizcacha rats are strictly herbivorous and are specialized for consuming halophytic plants. Plant species found in feces as well as in mound tunnels and food chambers include Allenrolfea vaginata, Suaeda divaricata, Atriplex lampa, Alternanthera nodifera, Atriplex argentina, and Heterostachys ritteriana (Diaz and Ojeda, 2000). In addition, dietary analysis suggests that they also feed on plants from the Verbenaceae, Nyctaginaceae, Solanaceae, Fabaceae, and Graminaceae plant families. However, Atriplex lampa accounts for about 76% of their diet (Mares et al., 1997).
Bristle brushes are an important structure that are unique to Tympanoctomys barrerae. Located posteriorly to the upper incisors, bristle brushes resemble a second set of the upper incisors. Bristle brushes, paired with lower incisors, strip the salt-filled surface from the leaves of halophytic plants prior to ingestion, which greatly reduces electrolyte consumption (Mares et al., 1997; Diaz and Ojeda, 2000). Similar to other desert rodents, Tympanoctomys barrerae uses its elongated renal papilla and relative medullary thickness to concentrate its urine, which allows it to excrete excess salt (Diaz and Ojeda, 2000). Bristle brushes and renal adaptations make T. barrerae highly adapted for the consumption of halophytic plants.
Plant Foods: leaves; wood, bark, or stems
Foraging Behavior: stores or caches food
Primary Diet: herbivore (Folivore , Lignivore)
Tympanoctomys barrerae is endemic to west-central and southern Argentina, between 29° south and 43° south (Ojeda, 2010). It is known from 8 localities in the provinces of San Juan, Mendoza, Neuquén, La Pampa, and Chubut of Argentina (Diaz and Ojeda, 2000; Odeja, 2010).
Biogeographic Regions: neotropical (Native )
The mating system for Tympanoctomys barrerae has not been determined.
Little information is available on reproduction in Tympanoctomys barrerae. On average, captive females have four litters per year (Diaz and Ojeda, 2000). Captive-born pups weigh about 4 g at birth and 8 g at five days old. They open their eyes at 6 days old and they can eat solid food at 10 days old (Diaz and Ojeda, 2000; Grzimek, 2004). Pups are not completely weaned by the time they begin eating solid food (Diaz and Ojeda, 2000).
Key Reproductive Features: iteroparous ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous
Little information exists regarding parental investment in red vizcacha rats. However, young are born in a precocial state and use saltbush and orache leaves (Genus: Atriplex) during foraging, which is thought to be learned from their mothers (Diaz and Ojeda, 2000). Although weaning age in wild red viscacha rats is unknown, captive-born pups nurse until they are at least 10 days old.
Parental Investment: precocial ; female parental care ; pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female)
The plains viscacha rat, plains vizcacha rat, red viscacha rat, or red vizcacha rat (Tympanoctomys barrerae) is a species of rodent in the family Octodontidae native to Argentina. It is one of three species in the genus Tympanoctomys.[3][4]
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]
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]
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 off and discard 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]
This species of rodent has (as of 2017) the largest number of chromosomes of any known mammal, 2n = 102.[10]
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,[11] while others have reasserted it.[12] The doubling of its chromosome number was presumably by errors in mitosis or meiosis within the animal's reproductive organs.[12] 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.[13] The animal's spermatozoa are roughly twice normal size, thought to be by virtue of having twice as many sets of chromosomes.[14]
The rodent is not a rat, but a caviomorph, kin to guinea pigs and chinchillas.
The plains viscacha rat, plains vizcacha rat, red viscacha rat, or red vizcacha rat (Tympanoctomys barrerae) is a species of rodent in the family Octodontidae native to Argentina. It is one of three species in the genus Tympanoctomys.
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