Tympanoctomys barreraeplains viscacha rat

Last updated:

Geographic Range

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). (Diaz and Ojeda, 2000; Ojeda, 2010)

Habitat

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). (Mares, et al., 1997a; Ojeda, 2010; Torres, et al., 2003)

  • Range elevation
    300 to 1,400 m
    984.25 to ft

Physical Description

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. (Diaz and Ojeda, 2000; Grzimek, 2004)

  • Sexual Dimorphism
  • male larger
  • Range mass
    51.8 to 104 g
    1.83 to 3.67 oz
  • Range basal metabolic rate
    .9 to 1.25 cm3.O2/g/hr

Reproduction

The mating system for Tympanoctomys barrerae has not been determined. (Grzimek, 2004)

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). (Diaz and Ojeda, 2000; Grzimek, 2004)

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. (Ojeda, 2010)

  • Parental Investment
  • precocial
  • female parental care
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female

Lifespan/Longevity

Little information exists regarding lifespan or longevity in red vizcacha rats.

Behavior

Red vizcacha rats are nocturnal rodents that live in complex burrow systems consisting of several entrance holes (Mares et al., 1997, Diaz and Ojeda, 2000). Research suggests that numerous entrances allow burrows to receive direct sunlight during winter and indirect sunlight throughout summer (Torres et al., 2003). Generally, entrances are located at the base of shrubs (Mares et al., 1997). Burrows also contain up to three levels of food chambers and tunnels (Diaz and Ojeda, 2000). The largest burrow recorded consisted of 33.7 m of tunnel. Along with their feces, the branches and leaves of saltbush (Genus: Atriplex) and seepweed (Genus: Suaeda) plants were found scattered throughout the tunnel system (Mares et al., 1997). Burrows are on average 13.59 m long, 8.71 m wide, and 1.25 m deep (Diaz and Ojeda, 2000). Each burrow may also have up to 14 satellite mounds within 3 m of the main burrow, which serve as alternate feeding sites or shelter. Only one individual resides in each burrow (Mares et al., 1997). (Diaz and Ojeda, 2000; Mares, et al., 1997a; Torres, et al., 2003)

Home Range

Little information is available on red vizcacha rats' mean territory size. (Diaz and Ojeda, 2000; Mares, et al., 1997a; Torres, et al., 2003)

Communication and Perception

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.

Food Habits

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). (Diaz and Ojeda, 2000; Mares, et al., 1997a; Mares, et al., 1997b)

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

Predation

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). (Diaz and Ojeda, 2000)

Ecosystem Roles

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). (Mares, et al., 1997a; Mares, et al., 1997b)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

There are no known positive effects of Tympanoctomys barrerae on humans. (Grzimek, 2004)

Economic Importance for Humans: Negative

There are no known adverse effects of Tympanoctomys barrerae on humans. (Grzimek, 2004)

Conservation Status

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. (Diaz and Ojeda, 2000; Gallardo, et al., 2006; Mares, et al., 1997a)

Other Comments

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). (Diaz and Ojeda, 2000; Gallardo, et al., 2002; Gallardo, et al., 2006)

Contributors

Jaclyn Ramsey (author), University of Wisconsin-Stevens Point, Stefanie Stainton (editor), University of Wisconsin-Stevens Point, Christopher Yahnke (editor), University of Wisconsin-Stevens Point, John Berini (editor), Animal Diversity Web Staff.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

folivore

an animal that mainly eats leaves.

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

herbivore

An animal that eats mainly plants or parts of plants.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

soil aeration

digs and breaks up soil so air and water can get in

solitary

lives alone

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

tactile

uses touch to communicate

terrestrial

Living on the ground.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

young precocial

young are relatively well-developed when born

References

Bozinovic, F., L. Contreras. 1990. Basal Rate of Metabolism and Temperature Regulation of Two Desert Herbivorous Octodontid Rodents: Octomys mimax and Tympanoctomys barrerae. Oecologia, Vol. 84, No. 4: 567-570.

Diaz, G., R. Ojeda. 2000. Tympanoctomys barrerae. Mammalian Species, No. 646: 1-4.

Gallardo, M., F. Mondaca, R. Ojeda, N. Kohler, O. Garrido. 2002. Morphological Diversity in the Sperms of Caviomorph Rodents. Mastozoologia Neotropical, Vol. 9, No. 2: 159-170.

Gallardo, M., R. Ojeda, C. Gonzalez, C. Rios. 2006. "The Octodontidae Revisited" (On-line). Accessed August 01, 2010 at http://lem.dm.cl/publicaciones/pdf/2006/OctoRevisitedFinal%202006.pdf.

Grzimek, B. 2004. Tympanoctomys barrerae. Pp. 438 in D Kleiman, V Geist, M McDade, eds. Grzimek's Animal Life Encyclopedia - Mammals, Vol. Vol. 16, Second Edition. Farmington Hills, MI: Gale.

Mares, M., J. Braun, R. Channell. 1997. Ecological Observations on the Octodontid Rodent, Tympanoctomys barrerae, in Argentina. The Southwestern Naturalist, Vol. 42, No. 4: 488-493.

Mares, M., R. Ojeda, C. Borghi, S. Giannoni, G. Diaz, J. Braun. 1997. How Desert Rodents Overcome Halophytic Plant Defenses. BioScience, Vol. 47, No. 10: 699-704.

Ojeda, A. 2010. Phylogeography and genetic variation in the South American rodent Tympanoctomys barrerae (Rodentia: Octodontidae). Journal of Mammalogy, Vol. 91, No. 2: 302-313.

Torres, R., C. Borghi, S. Giannoni, A. Pattini. 2003. Portal Orientation and Architecture of Burrows in Tympanoctomys barrerae (Rodentia, Octodontidae). Journal of Mammalogy, Vol. 84, No. 2: 541-546.