Rhizomyinae

Diversity

Rhizomyinae, the bamboo rats, is a small Old World family of fossorial muroid rodents. There are four species of bamboo rats in two genera ( Cannomys and Rhizomys ).

Geographic Range

Bamboo rats are distributed from Sumatra and the Malay Peninsula in the south through southern China, Nepal, and eastern India.

• Biogeographic Regions
• palearctic palearctic
  • native native
• oriental oriental
  • native native

Habitat

Rhizomyines live in bamboo thickets, forests, grassy areas, and gardens in hilly or mountainous regions, at elevations up to 4,000 meters. They burrow in a range of soil types, from loose and well-drained to hard and stony.

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

• Terrestrial Biomes
• savanna or grassland savanna or grassland
• forest forest
• mountains mountains

• Other Habitat Features
• agricultural agricultural

Physical Description

EXTERNAL CHARACTERISTICS

Rhizomyines are powerfully-built rodents with chunky bodies and short limbs. Their head and body length ranges from 147 to 480 mm, and their tail length ranges from 50 to 200 mm. They weigh 500 to 4,000 grams. There is no sexual dimorphism in size. Their short tails are hairless and lack scales. Their eyes and and external ears are small but not covered by fur. Bamboo rat fur ranges from soft, thick, and silky to coarse and sparse. The fur is colored slate gray, pinkish-gray, brownish-gray, chestnut, or cinnamon, and is paler on the belly than on the back in most species. Bamboo rats dig with their broad incisors, which protrude in front of the lips, and with their long, robust claws. The largest claw is on the third digit of the forefeet.

INTERNAL CHARACTERISTICS

The rhizomyine dental formula is 1/1, 0/0, 0/0, 3/3 = 16. The molars are hypsodont , and the molar rows run in parallel. The molars have mesolophs and mesolophids , giving them a pentalophodont enamel pattern, and they are nearly equal in size. The alveoli of the upper incisors end above the roots of the first molars, obstructing the orbits. The incisive foramena are short, and the bony palate is relatively smooth. The heavy mandible has prominant capsular and coronoid processes. Wide, strong zygomatic arches and the prominent sagittal and lambdoidal crests provide the broad attachment surfaces for the powerful head and neck muscles necessary for digging with their jaws. Due to the lack of the ventral portion of the infraorbital foramen , the zygomatic plate is poorly demarcated. The infraorbital foramen contains the nasolacrimal canal. The anterior portion of the lateral masseter muscle has a broad origin on the side of the wide, short rostrum , instead of on the zygomatic plate. The area between the orbits is constricted and the frontals are compressed. There are no sphenofrontal, stalacerate, or entepicondylar foramena. The pterygoid fossa is deep and well-ossified. The external auditory meatus is tubular in shape, the auditory bullae are moderately inflated, and the malleus is constructed perpendicularly. The interparietal bone is tiny. The rhizomyine stomach has two chambers, and the cecum has a spiral valve. There is no stapedial artery, and the internal carotid artery provides circulation to the orbits.

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

• Sexual Dimorphism
• sexes alike

Reproduction

The mating system of rhizomyines has not been reported.

Rhizomyines breed during the wet season, from February to April and again from August to October. Gestation lasts three to seven weeks, after which females give birth to litters of one to five young in an underground nest. The young develop slowly, growing hair at about two weeks, opening their eyes at about three weeks, and nursing until they are at least three months old (although they are capable of eating solid food at one month). The young reach adult size and sexual maturity when they are four to six months old.

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

Female bamboo rats build underground nests in which they raise their altricial young. They continue to nurse their young for over three months, even after the young are capable of eating solid food, and may forage with their young above ground. There is no male parental care known in this group.

• Parental Investment
• altricial altricial
• pre-fertilization
  • provisioning
  • 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 bamboo rats is three to four years.

Behavior

Bamboo rats are perhaps the least fossorial of the spalacids . Although they spend much of their time underground, they forage on the surface at night from time to time and some even climb bamboo. However, they move slowly when walking on the surface, with an awkward waddling gait. Underground, bamboo rats dig with their chisel-like incisors and strong foreclaws, and use their heads and feet to remove loose soil. They construct deep burrow systems consisting of a nest chamber, foraging tunnels, and bolt holes into which they can flee if threatened by predators. One bamboo rat may have several burrows. Generally, they are sedentary, but some have been known to migrate with the seasonal availability of food. Rhizomyines are nocturnal or crepuscular and they are active year-round. For the most part, they are solitary and territorial, although females have sometimes been seen foraging with their young.

• Key Behaviors
• fossorial fossorial
• nocturnal nocturnal
• crepuscular crepuscular
• motile motile
• migratory migratory
• sedentary sedentary
• solitary solitary
• territorial territorial

Communication and Perception

Bamboo rats perceive the world using vision, touch, smell, taste, and hearing. Given their small eyes and the fact that they spend most of their lives underground in complete darkness, vision is probably the least important of these senses. They are known to make grunting and tooth-grinding noises, which may be a form of communication, and it is likely that they use scent to communicate, as most mammals do.

• Communication Channels
• acoustic acoustic
• chemical chemical

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

Food Habits

Bamboo rats are herbivores that feed on the roots and shoots of bamboo and other plants. They also eat seeds and fruit if available. Bamboo rats store excess food in underground chambers in their burrow systems.

• Primary Diet
• herbivore herbivore
  • frugivore frugivore
  • granivore granivore

• Foraging Behavior
• stores or caches food stores or caches food

Predation

Bamboo rats fall prey to a variety of snakes , eagles , owls , and small mammalian carnivores . They probably avoid predation to some degree by staying hidden underground and only venturing forth under cover of darkness. Bamboo rats incorporate bolt holes into their burrow systems into which they can make a quick escape if caught out in the open. If cornered, they can be vicious and do not hesitate to rush at their attacker and attempt to bite.

Ecosystem Roles

Because of their fossorial lifestyle, bamboo rats probably help to aerate the soil. They are important consumers of bamboo and other plants, and they are prey for a variety of avian and mammalian predators. Where they are sympatric, different species of bamboo rats are potential competitors, but they avoid competition by partitioning microhabitats (i.e., by specializing on different species of bamboo).

• Ecosystem Impact
• soil aeration soil aeration

Economic Importance for Humans: Positive

Bamboo rats in northern Thailand are hosts of Penicillium marneffei , a pathogenic fungus that infects humans, especially those with HIV. However, it is not thought that bamboo rats transmit the fungus directly to humans; rather, that humans and bamboo rats become infected from a common environmental source. Therefore, research on bamboo rats may prove helpful for controlling outbreaks of P. marneffei in humans. Besides being valuable for disease research, bamboo rats are hunted and used as food by native peoples.

• Positive Impacts
• food food
• research and education

Economic Importance for Humans: Negative

Bamboo rats sometimes raid and damage tapioca and sugarcane crops.

• Negative Impacts
• crop pest

Conservation Status

Rhizomyines are still numerous in many areas, and none of the species in this subfamily are currently listed as threatened.

Other Comments

Fossil evidence suggests that the rhizomyine + tachyoryctine clade originated in the early Miocene of south Asia, about 20 million years ago. Tachyoryctines and rhizomyines then diverged about three million years later, and evolved their fossorial lifestyles separate from one another. Rhizomyines are thought to have evolved their fossorial lifestyle about 8.5 million years ago. The living rhizomyine genera appeared later, and are first represented by four-million-year-old fossils from the Pliocene of China.

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web.

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

References

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