kangaroo rat

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Kangaroo rats Fossil range: Late Pliocene - Recent
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Rodentia
Family:	Heteromyidae
Subfamily:	Dipodomyinae
Genus:	Dipodomys Gray, 1841
Species
Dipodomys agilis Dipodomys californicus Dipodomys compactus Dipodomys deserti Dipodomys elator Dipodomys gravipes Dipodomys heermanni Dipodomys ingens Dipodomys merriami Dipodomys microps Dipodomys nelsoni Dipodomys nitratoides Dipodomys ordii Dipodomys panamintinus Dipodomys phillipsii Dipodomys simulans Dipodomys spectabilis Dipodomys stephensi Dipodomys venustus

Kangaroo rats, genus Dipodomys, are small rodents native to North America. The common name derives from their bipedal form: as they hop in a manner similar to the much larger kangaroo, although they are not related.

Speciation

19 species of kangaroo rat are recognized. Their size varies from 10 to 20 cm, with a tail of equal or slightly greater length; the weight can be anywhere between 35 and 180 grams. The most distinctive feature of the kangaroo rats is their very long hind legs.

Like the jerboas of African and Asian deserts and the hopping mice of outback Australia, kangaroo rats have highly developed hind legs, live in deep burrows that shelter them from the worst of the desert heat, and do not lose water unless forced into a diet lacking in hydrocarbons.^[1] Instead, they have a highly water-efficient metabolism (their kidneys are at least four times more efficient at retaining water and excreting salt than those of humans) and manufacture water through a metabolic process called oxidative phosphorylation. These adaptations have prepared them to live in arid conditions. Despite sharing so many characteristics with jerboas and hopping mice, the three groups are not closely related to one another: the similarities are the result of convergent evolution.

Location and habitat

Kangaroo rats are found in arid and semi-arid areas of Canada, the United States and Mexico that retain some grass or other vegetation and thus fall under category xerocole. Their diet includes seeds, leaves, stems, buds, some fruit, and insects. Most kangaroo rat species use their burrows and buried caches nearby to store food against the possibility of bad seasons. The Banner-tailed Kangaroo Rat has been recorded making burrows with several storage chambers up to 25 cm in diameter each, and containing almost six kilograms of stored food.

Behavior

Kangaroo rats live in unknown environments in which food availability varies widely in space and time. The ability to hoard food is a vital adaptation. Food-hoarding is facilitated by the presence of external fur-lined cheek pouches that are used to transport food items from the harvest location to the storage site. The fur lining allows for seed transport with minimal water loss.

Two food-hoarding tactics are available to kangaroo rats: larderhoarding and scatterhoarding. The tactic employed varies greatly among species with some species using one tactic to the exclusion of the other and other species employing a combination of the two. Larderhoarding involves storing food items in large quantities at a central location, such as a burrow. Scatterhoarding involves the making of caches (in the form of small subsoil deposits) of food items throughout an individual’s home range. The costs and benefits of these tactics are variable for different species. Larderhoarding provides convenient access to large quantities of food, but the larder may vulnerable to catastrophic loss from competitors. Scatterhoarding may reduce the risk of catastrophic loss, but requires increased energy expenditure, exposure to predation risk and spatial memory. Additionally, competitors may also steal scatterhoards. There is little evidence available to determine what trade-off are involved in the use of one tactic over the other.

Anatomy

Unlike the jerboas and hopping mice, but like their close relatives the pocket mice, kangaroo rats have large cheek pouches that open on either side of the mouth and extend back to the shoulders. They fill the pouches with food , then empty them by turning them inside out, like pockets, with their forepaws. There is a special muscle that, once the pouch is empty and clean, pulls it back in again.

The overall color of the kangaroo rats can be anywhere between pale, sandy yellow, and dark brown, with a white underside and often with white banding across the thighs. Tails tend to be dark with white sides and a tuft of longer hairs. Facial markings vary from one species to another, but all have an oil gland between the shoulders.

A feature of the kangaroo rat is the animal's efficient kidneys. The kangaroo rat has a longer loop of Henle in the nephrons which permit a greater magnitude of countercurrent multiplication and thus a larger medullary vertical osmotic gradient. As a result, these rodents can produce urine that is concentrated up to an osmolarity of almost 6,000 mosm/liter, which is five times more concentrated than maximally concentrated human urine at 1,200 mosm/liter. Because of this tremendous concentration ability, kangaroo rats never have to drink; the H₂O produced metabolically within their cells during oxidation of foodstuff (food plus O₂ yields CO₂ + H₂O + energy) is sufficient for their body. Also, kangaroo rats cannot lose water by perspiring, because they have no sweat glands. Kangaroo rats lose so little water that they can recover 90% of the loss by using metabolic water gaining the remaining 10% from the small amount of water in their diet.

Kangaroo rats lose water mainly by evaporation during gas exchange, and so have developed a behavioural adaptation to prevent this loss. As they spend a lot of time within their burrows to escape the heat of the day, the burrows become much more humid than the air outside (due to evaporative loss). When collecting seeds, they store them in the burrows rather than eating them straight away. This causes the moisture in the air to be absorbed by the seeds, and the kangaroo rat regains the water it has previously lost when it then consumes them.

Taxonomy

• Family Heteromydae
  • Subfamily Dipodomyinae
    • Dipodomys agilis (Agile kangaroo rat)
    • Dipodomys californicus (California kangaroo rat)
    • Dipodomys compactus (Gulf Coast kangaroo rat)
    • Dipodomys deserti (Desert kangaroo rat)
    • Dipodomys elator (Texas kangaroo rat)
    • Dipodomys gravipes (San Quintin kangaroo rat)
    • Dipodomys heermanni (Heerman's kangaroo rat)
    • Dipodomys ingens (Giant kangaroo rat)
    • Dipodomys merriami (Merriam's kangaroo rat)
    • Dipodomys microps (Chisel-toothed kangaroo rat)
    • Dipodomys nelsoni (Nelson's kangaroo rat)
    • Dipodomys nitratoides (Fresno kangaroo rat)
    • Dipodomys ordii (Ord's kangaroo rat)
    • Dipodomys panamintinus (Panamint kangaroo rat)
    • Dipodomys phillipsii (Phillip's kangaroo rat)
    • Dipodomys simulans (Dulzura Kangaroo Rat)
    • Dipodomys spectabilis (Banner-tailed kangaroo rat)
    • Dipodomys stephensi (Stephen's kangaroo rat)
    • Dipodomys venustus (Narrow-faced kangaroo rat)

References

• Patton, J. L. 2005. Family Heteromyidae. Pp. 844-858 in Mammal Species of the World a Taxonomic and Geographic Reference. D. E. Wilson and D. M. Reeder eds. Johns Hopkins University Press, Baltimore.

External links

• Life History of the Kangaroo Rat at Project Gutenberg --United States Department of Agriculture Bulletin No. 1091, from September 1922

See also

• Kangaroo mouse
• Springhare