Tympanoctomys barrerae

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).

• Biogeographic Regions
• neotropical neotropical
  • native native

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).

• Habitat Regions
• terrestrial terrestrial

• Terrestrial Biomes
• desert or dune desert or dune

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.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger

Reproduction

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 iteroparous
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• viviparous 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 precocial
• female parental care 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).

• Key Behaviors
• fossorial fossorial
• nocturnal nocturnal
• motile motile
• solitary solitary

Home Range

Little information is available on red vizcacha rats' mean territory size.

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.

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

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).

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.

• Primary Diet
• herbivore herbivore
  • folivore folivore
  • lignivore

• Plant Foods
• leaves
• wood, bark, or stems

• Foraging Behavior
• stores or caches food stores or caches food

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).

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 ).

• Ecosystem Impact
• creates habitat
• soil aeration soil aeration

Economic Importance for Humans: Positive

There are no known positive effects of Tympanoctomys barrerae on humans.

Economic Importance for Humans: Negative

There are no known adverse effects of Tympanoctomys barrerae on humans.

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.

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).

Additional Links

Encyclopedia of Life

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.

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., 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 .

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.

Grzimek, B. 2004. Tympanoctomys barrerae. Pp. 438 in 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.