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Psammomys obesusfat sand rat

By Tara Biagi

Geographic Range

Psammomys obesus, the fat sand rat, is found in North Africa, ranging from Mauritania to Egypt and Sudan, and east across the Arabian Peninsula. (Harrison, 1972; Mendelsshon and Yom-Tov, 1999)

Habitat

Fat sand rats are terrestrial mammals that are most often found in sandy deserts, but can be found in rocky terrain, saline-marsh areas, and loess plains. They live in burrows composed of large mouthed holes which are located near and under the bushes where they forage. (Harrison, 1972; Mendelsshon and Yom-Tov, 1999; Nowak, 1999)

Physical Description

The head and body length of P. obesus is 130 to 185mm, while the tail length is 110 to 150mm. Males weigh between 125 and 208g and females weigh between 146 and 207g. Psammomys obesus are heavily built, rat-like gerbils with fully haired and tufted tails. The tuft of hair on the end of the tail measures about 14mm. They have large, black eyes, robust limbs, and heavy feet with black 4 to 5mm claws. The skin is also black, most likely to protect them from the sun’s ultraviolet rays. The features used distinguish P. obesus are their nongrooved incisors and their very short, round ears.

Dorsal fur varies from light-brown to red to yellow and is speckled with black. The underbelly is a grayish/white, with the area under the chin slightly whiter than the rest of the ventral surface. The last third of the tail is black, including the tuft, while the underside is whitish.

Sexual dimorphism has not been noted in P. obesus. (Harrison, 1972; Mendelsshon and Yom-Tov, 1999; Nowak, 1999)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    125 to 208 g
    4.41 to 7.33 oz
  • Range length
    130 to 185 mm
    5.12 to 7.28 in

Reproduction

Little information on the mating systems of P. obesus is available. However, the fact that dominant male home ranges are large, encompassing home ranges of several females, suggests that these males will mate with the multiple females within their home range. (Harrison, 1972)

In the wild, P. obesus is born between December and April. In captivity they can breed year round. The breeding season is dependent on the availability of food and, therefore, on the amount of rainfall. In times of drought or little rainfall, breeding has been known to stop almost completely. Gestation lasts 24 days. Litter size of ranges from 1 to 7 young. The young are born hairless, opening their eyes after one week, with weaning occurring after three weeks. Young are independent upon weaning. Females can conceive after 3 to 3.5 months of age while sexual maturity for males is reached at 4 months. Because of their short lifespan in the wild, P. obesus individuals only breed for one season, however they can give birth 2 to 4 times per season. (Mendelsshon and Yom-Tov, 1999; Nowak, 1999)

  • Breeding interval
    Fat sand rats can breed 2 to 4 times per season.
  • Breeding season
    Fat sand rats breed between December and April.
  • Range number of offspring
    1 to 7
  • Average number of offspring
    3.5
    AnAge
  • Range gestation period
    24 to 36 days
  • Average weaning age
    3 weeks
  • Average time to independence
    3 weeks
  • Average age at sexual or reproductive maturity (female)
    3 months
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    100 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    4 months

Only female fat sand rats take care of the young. Young are nursed and cared for by their mother in her den until soon before they are weaned and become independent. (Mendelsshon and Yom-Tov, 1999)

  • Parental Investment
  • no parental involvement
  • altricial
  • female parental care
  • pre-fertilization
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

The lifespan of P. obesus in the wild is about 14 months while those in captivity can live between three and four years.

  • Average lifespan
    Status: wild
    14 months
  • Average lifespan
    Status: captivity
    3-4 years
  • Average lifespan
    Status: captivity
    3.2 years
    AnAge

Behavior

Fat sand rats are diurnal, with daytime activity depending on the temperature of their aboveground surroundings. In winter they may emerge for about five hours during the middle of the day. During the summer they are mainly active in the early morning and afternoon hours to avoid intense midday heat. In certain areas, fat sand rats will be active at night if the ambient temperature is warm enough. Throughout the winter they often bask in the sun, flattening their body and spreading their limbs out to absorb the heat.

Some behaviors of P. obesus are similar to those of American prairie dogs (Cynomys) in that they sit up on their hind legs and tail to observe danger and retreat to their burrows when alarmed.

It has been noted that fat sand rats use only one hand to hold their food, they wipe leaves before eating them, and comb their fur with their forefeet. (Harrison, 1972; Mendelsshon and Yom-Tov, 1999; Nowak, 1999)

  • Range territory size
    75.8 (low) m^2
  • Average territory size
    189.6 m^2

Home Range

The average home range is 189.6m^2 for males and 75.8m^2 for females. Female fat sand rats have small home ranges and tend to stay near the bushes they use for food, only moving when their food source is depleted. Like females, subordinate males also have small ranges, but they move more often than the females. Dominant males have wide ranges that may include the ranges of several females and subordinate males.

Fat sand rats have extensive burrows systems with 3-5 openings consisting of complicated tunnels with storage chambers, toilet chambers, and nests for sleeping. They are colonial, but each burrow system holds one adult with the exception of breeding when a pair or a family occupies one system. (Harrison, 1972; Mendelsshon and Yom-Tov, 1999; Nowak, 1999)

Communication and Perception

Psammomys obesus communicate with each other using high-pitched squeaks and foot drumming. It is unknown what kinds of communications these are, though the sounds may be used to warn against predators. Fat sand rats probably also use olfactory cues extensively to communicate home range boundaries and reproductive state.

Fat sand rats have keen senses of smell, vision, and hearing. Touch can be an important way of sensing the environment and communicating with conspecifics. (Mendelsshon and Yom-Tov, 1999; Nowak, 1999)

Food Habits

Fat sand rats feed on the leaves of succulent plants, particularly salt bushes of the Chenopodiaceae family. Because these plants contain mostly water and salt, large amounts of leaves must be ingested in order to get enough nutrients. They can survive eating the salty plants without an abundance of water because they have extremely efficient kidneys that can excrete highly concentrated urine (about 18 times as concentrated as humans). Fat sand rats have also been known to eat grains such as barley. (Harrison, 1972; Mendelsshon and Yom-Tov, 1999; Nowak, 1999)

  • Plant Foods
  • leaves
  • wood, bark, or stems
  • seeds, grains, and nuts

Predation

Fat sand rats are preyed upon by many small predators, such as snakes, including those in the genus Spalerosophis, owls, other birds of prey, and jackals (Canis aureus). They escape predation through their vigilance, taking refuge in burrows, and through their cryptic coloration. (Harrison, 1972; Mendelsshon and Yom-Tov, 1999)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Because fat sand rats live under and eat the leaves of Chenopodiaceae species, they may have an impact on the populations of these bushes. However, this has not been documented. Fat sand rats are an important prey base for small to medium-sized predators in the ecosystems in which they live.

Economic Importance for Humans: Positive

Psammomys obesus can easily acquire non insulin dependent diabetes mellitus and the complications associated with diabetes (cataracts, pancreatic atrophy, and impaired renal function) from high caloric foods such as laboratory rodent pellets. For this reason, fat sand rats are used as a model species to study diabetic mellitus and its complications. (Mendelsshon and Yom-Tov, 1999; Murray, et al., 2004)

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

Fat sand rats are known to be carriers of the parasitic disease Leishmaniasis. This disease can be transferred to humans from P. obesus by the sand fly Phlebotomus. (Mendelsshon and Yom-Tov, 1999)

Conservation Status

Psammomy obesus does not appear to be a threatened or endangered species.

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Tara Biagi (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

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.

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

chemical

uses smells or other chemicals to communicate

crepuscular

active at dawn and dusk

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

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.

diurnal
  1. active during the day, 2. lasting for one day.
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).

marsh

marshes are wetland areas often dominated by grasses and reeds.

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.

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

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

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

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

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.

References

The Tisch Family Zoological Gardens in Jerusalem. 2004. "The Tisch Family Zoological Gardens in Jerusalem: The Biblical Zoo" (On-line). Accessed March 29, 2004 at http://www.jerusalemzoo.org.il/english/upload/month/psammomys.html.

Harrison, D. 1972. The Mammals of Arabia: Volume III. London: Ernest Benn Limited.

Mendelsshon, H., Y. Yom-Tov. 1999. Fauna Palestina: Mammalia of Israel. Jerusalem: Israel Academy of Sciences and Humanities.

Murray, L., S. Dalal, P. Rico, V. Chenault. 2004. Evaluation of The Estrous Cycle in the Sand Rat, (Psammomys obesus), an Animal Model of Nutritionally Induced Diabetes Mellitus. Online Journal of Veterinary Research, Volume 8: 7-15. Accessed March 30, 2004 at http://www.comcen.com.au/~journals/ojvr/abstracts2004/sandratabs2004.htm.

Nowak, R. 1999. Walker's Mammals of the World. Baltimore: Johns Hopkins University Press.

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