Rhizomyinaebamboo rats and mole rats

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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). (Musser and Carleton, 2005)

Geographic Range

Bamboo rats are distributed from Sumatra and the Malay Peninsula in the south through southern China, Nepal, and eastern India. (Carleton and Musser, 1984)

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. (Carleton and Musser, 1984; Nevo, 1999; Nowak, 1999)

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. (Carleton and Musser, 1984; Nevo, 1999; Nowak, 1999)

  • 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. (Carleton and Musser, 1984; Flynn, 1990; Nevo, 1999; Nowak, 1999)

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. (Flynn, 1990; Nowak, 1999)

  • Parental Investment
  • 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. (Nevo, 1999; Nowak, 1999)

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. (Carleton and Musser, 1984; Flynn, 1990; Nevo, 1999; Nowak, 1999)

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. (Nowak, 1999)

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. (Carleton and Musser, 1984; Nowak, 1999)

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. (Carleton and Musser, 1984; Nevo, 1999; Norris, et al., 2004)

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). (Nevo, 1999)

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. (Chariyalertsak, et al., 1996; Chariyalertsak, et al., 1997; Nowak, 1999)

  • Positive Impacts
  • food
  • research and education

Economic Importance for Humans: Negative

Bamboo rats sometimes raid and damage tapioca and sugarcane crops. (Nowak, 1999)

  • 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. (IUCN, 2004)

  • IUCN Red List [Link]
    Not Evaluated

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. (Flynn, 1990; Nevo, 1999)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Allison Poor (author), 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

agricultural

living in landscapes dominated by human agriculture.

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.

chemical

uses smells or other chemicals to communicate

crepuscular

active at dawn and dusk

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.

food

A substance that provides both nutrients and energy to a living thing.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

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.

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).

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

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

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

soil aeration

digs and breaks up soil so air and water can get in

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.

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.

References

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.

Chariyalertsak, S., T. Sirisanthana, K. Supparatpinyo, J. Praparattanapan, K. Nelson. 1997. Case-control study of risk factors for Penicillium marneffei infection in human immunodeficiency virus-infected patients in Northern Thailand. Clinical Infectious Diseases, 24 (6): 1080-1086.

Chariyalertsak, S., P. Vanittanakom, K. Nelson, T. Sirisanthana, N. Vanittanakom. 1996. Rhizomys sumatrensis and Cannomys badius, new natural animal hosts of Penicillium marneffei. Journal of Medical and Veterinary Mycology, 34 (2): 105-110.

Ellerman, J. 1940. The Families and Genera of Living Rodents, vol. I. London: British Museum (Natural History).

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

Flynn, L. 1990. The natural history of rhizomyid rodents. Pp. 155-183 in E Nevo, O Reig, eds. Evolution of Subterranean Mammals at the Organismal and Molecular Levels. New York: Wiley-Liss.

IUCN, 2004. "2004 IUCN Red List of Threatened Species" (On-line). Accessed May 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(11): 2017-2031.

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

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. Washington, D.C.: Smithsonian Institution Press.

Nevo, E. 1999. Mosaic Evolution of Subterranean Mammals. Oxford: Oxford University Press.

Norris, R., K. Zhou, C. Zhou, G. Yang, C. Kilpatrick, R. Honeycutt. 2004. The phylogenetic position of the zokors (Myospalacinae) and comments on the families of muroids (Rodentia). Molecular Phylogenetics and Evolution, 31: 972-978.

Nowak, R. 1999. Walker's Mammals of the World, vol. 2. Baltimore and London: The Johns Hopkins University Press.

Potapova, E., N. Vorontsov. 2004. Taxonomic position of the genus Tachyoryctes and mutual relations between Rhizomyidae and Spalacidae families (Rodentia). Zoologicheskii Zhurnal, 83(8): 1044-1058.

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.

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