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)
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)
- Other Habitat Features
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)
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)
- Key Reproductive Features
- year-round breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
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
Deomyines live two to four years in captivity; lifespan in the wild is undoubtedly shorter. (Carey and Judge, 2002)
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)
- Other Communication Modes
- scent marks
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)
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
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)
Economic Importance for Humans: Positive
There are no known positive effects of otomyines on humans.
Economic Importance for Humans: Negative
- Negative Impacts
- carries human disease
- crop pest
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
Otomyines appear in the fossil record in the late Pliocene of South Africa. (Carleton and Musser, 1984)
Tanya Dewey (editor), Animal Diversity Web.
Allison Poor (author), University of Michigan-Ann Arbor.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
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.
an animal that mainly eats meat
uses smells or other chemicals to communicate
an animal that mainly eats the dung of other animals
active at dawn and dusk
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.
- 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
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.
an animal that mainly eats leaves.
Referring to a burrowing life-style or behavior, specialized for digging or burrowing.
an animal that mainly eats fruit
an animal that mainly eats seeds
An animal that eats mainly plants or parts of plants.
An animal that eats mainly insects or spiders.
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).
marshes are wetland areas often dominated by grasses and reeds.
makes seasonal movements between breeding and wintering grounds
having the capacity to move from one place to another.
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.
active during the night
an animal that mainly eats all kinds of things, including plants and animals
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
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
uses touch to communicate
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).
Living on the ground.
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
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.
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.
uses sight to communicate
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
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