Otomyinae

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.

Geographic Range

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

• Biogeographic Regions
• ethiopian ethiopian
  • native native

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.

• Habitat Regions
• temperate temperate
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• desert or dune desert or dune
• savanna or grassland savanna or grassland
• mountains mountains

• Wetlands
• marsh marsh
• swamp swamp

• Other Habitat Features
• riparian riparian

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.

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

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).

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.

• Key Reproductive Features
• iteroparous iteroparous
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• viviparous viviparous

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.

• Parental Investment
• precocial 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.

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.

• Key Behaviors
• cursorial
• terricolous
• fossorial fossorial
• diurnal diurnal
• nocturnal nocturnal
• crepuscular crepuscular
• motile motile
• migratory migratory
• sedentary sedentary
• solitary solitary
• territorial territorial
• social social
• dominance hierarchies dominance hierarchies

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.

• Communication Channels
• visual visual
• acoustic acoustic
• chemical chemical

• Other Communication Modes
• scent marks scent marks

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

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.

• Primary Diet
• carnivore carnivore
  • insectivore insectivore
• herbivore herbivore
  • folivore folivore
  • frugivore frugivore
  • granivore granivore
  • lignivore
• omnivore omnivore
• coprophage coprophage

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.

• Anti-predator Adaptations
• cryptic 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 .

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.

• 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.

Other Comments

Otomyines appear in the fossil record in the late Pliocene of South Africa.

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web.

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

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 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 The Mammals of Africa. An Identification Manual . Washington, D.C.: Smithsonian Institution Press.

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

Musser, G., M. Carleton. 2005. Superfamily Muroidea. 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.