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Otomyinaevlei rats and whistling rats

By Allison Poor

Diversity

Otomyinae is one of the smaller subfamilies of muroid rodents, with 23 species in 3 genera: Myotomys, Otomys, and Parotomys. This Old World subfamily includes the vlei rats, whistling rats, and karoo rats. (Musser and Carleton, 2005)

Geographic Range

Otomyines are native to southern and east central Africa, with an isolated population in Cameroon and Nigeria (Otomys occidentalis). (Carleton and Musser, 1984)

Habitat

Otomyines live in deserts, veldts, grasslands, savannahs, swamps, marshes, stream borders, alpine meadows, and areas of brushy secondary growth. They are found at elevations up to 4,000 meters. (Carleton and Musser, 1984; Nowak, 1999)

Physical Description

Otomyines are medium-sized, volelike muroid rodents with stocky bodies, rounded profiles, short hind feet, small eyes, and small ears. Their head and body length ranges from 124 to 217 mm, their tails range from 55 to 150 mm, and they weigh 60 to 255 grams. Otomyines have long, dense, soft fur that varies in color from pale buff to brown to reddish to rusty-yellow with black or brown streaks. The underparts and sides of the body tend to be paler, and are white, grayish white, cream, buff, brown, or gray.

The otomyine dental formula is 1/1, 0/0, 0/0, 3/3 = 16. They have wide, opisthodont incisors. The molars are rooted, and the crowns consist of transverse crests of enamel, with no individually demarcated cusps. The first upper molars each have three of these crests, while the second upper and second and third lower molars each have two. The third upper molars and first lower molars have a variable number of crests. Skull features include a large interparietal bone; somewhat enlarged mastoid bullae; a narrow mesopterygoid fossa that extends between the third molars; long, narrow incisive foramina; a separation of the masticatory foramen and accessory foramen ovale by a strut of the alisphenoid bone; and the presence of an accessory tympanum. Otomyines have single-chambered stomachs and complex ceca. (Carleton and Musser, 1984; Nowak, 1999)

Reproduction

The mating system of otomyines has not been explicitly studied, and it may vary substantially by species. Some species do not breed in captivity when housed as male/female pairs (Davis 1972), but others do (Pillay 2001). (Davis, 1972; Pillay, 2001)

Otomyines reproduce year round, although in some areas breeding peaks during the wet season. Females produce up to five litters per year. Gestation lasts about 40 days. Litters consist of one to five, usually two to three, relatively precocial young. The young develop quickly. They gain the ability to smell at birth or a few days afterward, and some are born well-furred with functional eyes and ears. By the second week, they have been observed running around and carrying objects in their mouths, presumably in play (Davis 1972). Young otomyines commonly practice allogrooming by day 14, by which time they are also weaned. They become sexually mature at 5 to 13 weeks, with females maturing a few weeks earlier than males. (Carleton and Musser, 1984; Davis, 1972; Nowak, 1999; Pillay, 2001)

Young otomyines are relatively precocial. They have their incisors at birth and they cling tenaciously to their mothers' nipples for the first 7 days or so. Females of some species may drag their young around with them while foraging. Some female otomyines do not carry their babies in their mouths, as the young are highly mobile fairly early in life. Also, mothers do not groom their offspring as much as do some other rodents, because the young can groom themselves after just a few days. After a couple of weeks, they can groom their mothers. When the young begin eating solid food, 6 or 7 days after birth, they may squabble over food items with their mothers, threatening them as they would threaten intruders as adults, their mothers seem to ignore these threats. (Pillay, 2001; Carleton and Musser, 1984; Davis, 1972; Nowak, 1999; Pillay, 2001)

  • Parental Investment
  • precocial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • protecting
      • female

Lifespan/Longevity

Deomyines live two to four years in captivity; lifespan in the wild is undoubtedly shorter. (Carey and Judge, 2002)

Behavior

Otomyines are terrestrial rodents. They are often described as being wary and quick to seek shelter at the slightest hint of danger. Some species are diurnal, and others are nocturnal, crepuscular, or active both day and night. They are active year round.

Some otomyine species construct nests out of sticks and other plant material and place these in burrows, on the ground surface, or in low shrubs above the entrances to burrows. Others do not build nests at all. Burrows may be complex systems of underground tunnels with multiple entrances or simple holes in the ground. Otomyines often make networks of above-ground runways through the grass, which radiate outward from a burrow or surface nest. These runways are sometimes marked by small piles of grass clippings left behind during their construction.

Otomyines are generally cursorial, but they are known to swim and dive to escape predators. Most are sedentary, but those that live near water may migrate during the wet season to avoid being flooded out.

These rodents range in social habits from gregarious, living in pairs or small family groups, to solitary, aggressive, and territorial. They seem to have well-defined home ranges, but these home ranges may overlap with one another. In one study, males were noted to be dominant over females, and heavier animals were dominant over lighter animals (Davis 1972). Also, males and females housed in pairs became mutually tolerant, whereas intrasex pairs always fought. (Carleton and Musser, 1984; Davis, 1972; Nowak, 1999)

Communication and Perception

Otomyines perceive their world through vision, hearing, olfaction, taste, and touch. Of these, vision may be less important, whereas hearing and olfaction seem quite keen (Davis 1972). Among Otomys irroratus, Davis (1972) noted that individuals confronted by new objects or environments spent a long time sniffing their unfamiliar surroundings and touching unfamiliar objects with their vibrissae.

Otomyines use visual, auditory, and olfactory signals to communicate with one another. Individuals sniff one another's noses upon meeting, and during social conflicts, they often utter a metallic-sounding chirp. Body posturing also plays a role in social interactions; in one study on O. irroratus, dominant individuals were seen to approach subordinate individuals in a flattened crouch, whereas subordinate individuals adopted an upright posture (Davis 1972). They were also seen to vibrate their tails quickly back and forth as a sign of aggression. Otomyines mark their territories with urine and with secretions from their anal glands. Young otomyines that have been separated from their mothers squeak loudly so that she can locate them, and mothers seem to recognize their offpring by scent. Some species make whistling noises and/or stamp their hind feet when alarmed. (Carleton and Musser, 1984; Davis, 1972; Nowak, 1999)

Food Habits

Otomyines are primarily herbivorous. They eat grasses, roots, shoots, bark, forbs, seeds, and berries, and sometimes insects. Otomyines have been known to practice coprophagy, especially during times of food shortage. (Carleton and Musser, 1984; Davis, 1972; Nowak, 1999)

Predation

Small mammalian carnivores, snakes, and birds of prey including hawks and owls prey upon otomyines. No doubt their vigilance, agility, and cryptic coloration help them to avoid predation. (Carleton and Musser, 1984)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

In general, otomyines are primary consumers. They, in turn, are preyed upon by a number of secondary consumers. In addition, otomyines are parasitized by several flea species, including Dinopsyllus titan, D. longifrons, Ctenopthalmus evidens, and C. cophurus. (Hubbard, 1972)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

There are no known positive effects of otomyines on humans.

Economic Importance for Humans: Negative

Otomyines may carry plague in some locations. In addition, these rodents are known to damage trees in nurseries by gnawing the bark. (Hubbard, 1972; Nowak, 1999)

  • Negative Impacts
  • injures humans
    • carries human disease
  • crop pest

Conservation Status

Currently, the IUCN considers three otomyine species to be endangered (Barbour's vlei rats, Otomys barbouri, Mt. Elgon vlei rats, Otomys jacksoni, and Uzungwe vlei rats, Otomys uzungwensis), three to be vulnerable (Burton's vlei rats, Otomys burtoni, Ruwenzori vlei rats, Otomys dartmouthi, and western vlei rats, Otomys occidentalis), and two to be near threatened (Dent's vlei rats, Otomys denti and Tanzanian vlei rats, Otomys lacustris). Another two lack sufficient data to be assessed (Afroalpine vlei rats, Otomys orestes and Dollman's vlei rats, Otomys dollmani). The species that are on the IUCN's list are there because their ranges are very small, highly fragmented, or both. Preserves have been established that may slow the decline of some species, but research is still needed that will allow the creation of comprehensive management plans. (IUCN, 2004)

  • IUCN Red List [Link]
    Not Evaluated

Other Comments

Otomyines appear in the fossil record in the late Pliocene of South Africa. (Carleton and Musser, 1984)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Allison Poor (author), University of Michigan-Ann Arbor.

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coprophage

an animal that mainly eats the dung of other animals

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.
dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

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.

folivore

an animal that mainly eats leaves.

fossorial

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

frugivore

an animal that mainly eats fruit

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

insectivore

An animal that eats mainly insects or spiders.

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.

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

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

nocturnal

active during the night

omnivore

an animal that mainly eats all kinds of things, including plants and animals

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

sedentary

remains in the same area

sexual

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

social

associates with others of its species; forms social groups.

solitary

lives alone

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

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.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

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.

year-round breeding

breeding takes place throughout the year

young precocial

young are relatively well-developed when born

References

Bohmann, L. 1953. Die afrikanische Nagergattung Otomys F. Cuvier. Zeitschrift Saugetierk, 18: 1-80.

Carey, J., D. Judge. 2002. "Longevity Records: Life Spans of Mammals, Birds, Amphibians, Reptiles, and Fish" (On-line). Max Planck Institute for Demographic Research. Accessed June 20, 2005 at http://www.demogr.mpg.de/.

Carleton, M., G. Musser. 1984. Muroid rodents. Pp. 289-379 in S Anderson, J Jones Jr., eds. Orders and Families of Recent Mammals of the World. New York: John Wiley and Sons.

Chaline, J., P. Mein, F. Petter. 1977. Les grandes lignes d'une classification évolutive des Muroidea. Mammalia, 41: 245-252.

Corbert, G., J. Hill. 1980. A World List of Mammalian Species. London: British Museum (Natural History).

Davis, R. 1972. Behavior of the vlei rat, Otomys irroratus (Brants, 1827). Zoologica Africana, 7(1): 119-140.

Ellerman, J. 1941. The Families and Genera of Living Rodents, vol. II. London: British Museum (Natural History).

Hubbard, C. 1972. Observations on the life histories and behavior of some small rodents from Tanzania. Zoologica Africana, 7(2): 419-449.

IUCN, 2004. "2004 IUCN Red List of Threatened Species" (On-line). Accessed June 20, 2005 at www.redlist.org.

Jansa, S., M. Weksler. 2004. Phylogeny of muroid rodents: relationships within and among major lineages as determined by IRBP gene sequences. Molecular Phylogenetics and Evolution, 31: 256-276.

Michaux, J., A. Reyes, F. Catzeflis. 2001. Evolutionary history of the most speciose mammals: molecular phylogeny of muroid rodents. Molecular Biology and Evolution, 18: 2017-2031.

Miller, G., J. Gidley. 1918. Synopsis of supergeneric groups of rodents. Journal of the Washington Academy of Science, 8: 431-448.

Misonne, X. 1971. Rodentia. Pp. 1-39 in J Meester, H Setzer, eds. The Mammals of Africa. An Identification Manual. Washington, D.C.: Smithsonian Institution Press.

Musser, G., M. Carleton. 1993. Family Muridae. Pp. 501-753 in D Wilson, D Reeder, eds. Mammal Species of the World. Washington, D.C.: Smithsonian Institution Press.

Musser, G., M. Carleton. 2005. Superfamily Muroidea. D Wilson, D Reeder, eds. Mammal Species of the World. Baltimore and London: The Johns Hopkins University Press.

Nowak, R. 1999. Walker's Mammals of the World, vol. II. Baltimore and London: The Johns Hopkins University Press.

Pillay, N. 2001. Reproduction and postnatal development in the bush Karoo rat Otomys unisulcatus (Muridae, Otomyinae). Journal of Zoology, 254: 515-520.

Roberts, A. 1951. The Mammals of South Africa. South Africa: Central News Agency.

Simpson, G. 1945. The principles of classification and a classification of mammals. Bulletin of the American Museum of Natural History, 85: 1-350.

Steppan, S., R. Adkins, J. Anderson. 2004. Phylogeny and divergence-date estimates of rapid radiations in muroid rodents based on multiple nuclear genes. Systematic Biology, 53(4): 533-553.

Thomas, O. 1896. On the genera of rodents: an attempt to bring up to date the current arrangement of the order. Proceedings of the Zoological Society of London: 1012-1028.

Tullberg, T. 1899. Uber das system der nagethiere: eine phylogenetische studie. Nova Acta Regiae Societatis Scientiarum Upsaliensis, 3: 1-514.

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