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Muroideamice, rats, gerbils, and relatives

By Phil Myers and Allison Poor

Diversity

The superfamily Muroidea includes most of the familiar rats and mice, but it also encompasses an enormously diverse array of other rodents. Currently there are 1517 recognized species and 310 genera of muroid rodents. These are divided among six families: Platacanthomyidae (Oriental dormice), Spalacidae (zokors, blind mole-rats, bamboo rats, root rats), Calomyscidae (mouse-like hamsters), Nesomyidae (climbing mice, African rock mice, Malagasy rats and mice, swamp mice, pouched rats, white-tailed rat), Cricetidae (hamsters, voles, lemmings, New World rats and mice), and Muridae (true mice and rats, gerbils). (Musser and Carleton, 2005)

Geographic Range

Members of the superfamily Muroidea can be found on all continents except Antarctica and on many oceanic islands. (Nowak, 1999)

Habitat

Muroid rodents occupy ecosystems ranging from dry desert to wet tropical forest, from tundra to savanna to temperate woodland. Some species are semiaquatic; others live underground; yet others spend their entire lives in the canopy of tropical forest. (Nowak, 1999)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

Physical Description

A number of characters link most muroids. Not surprisingly, even the most basic characters are subject to continuing evolutionary change; most of the characters listed as diagnostic in the next paragraph do in fact show some variation within the group. All, however, are believed to have characterized primitive muroids.

In the skull of muroids, the infraorbital foramen, which primitively transmits nerves to the rostral region of the skull, lies mostly above the zygomatic plate. It is enlarged above for the passage of a slip of muscle that inserts on the lower jaw, and narrowed in its lower region, through which pass nerves and blood vessels en route to the rostrum. The foramen thus has a distinctive "keyhole" shape in most forms (but the narrow ventral portion is lost in a few species). The zygomatic plate, formed by the anterior base of the zygomatic arch, is broad and a conspicuous feature of the cranium. From it arise other parts of the same muscle (the masseter) that passes through the infraorbital foramen. The jugal, one of the bones that participates in the zygomatic arch, is small and does not contact the lacrimal. The frontals are constricted above the orbits and there is no postorbital process or bar. Posteriorly, an interparietal bone is present and usually conspicuous.

The lower jaw is sciurognathus. As in all rodents, one upper and one lower incisor are always found on each side of the jaw, and canines are always absent. Following the incisor is a diastema. Canines and premolars are never present. No more than three molars occur on each side, but this number is sometimes reduced to two or even one. The nature of the molars (shape, size, surface structure, number of roots) varies greatly.

Four clawed digits are found on each forefoot (the pollex or "thumb" is small and bears a nail); the hind foot in most has five clawed digits (but sometimes the hallux or first toe has a nail). Other external features (ears, eyes, tail, pelage, etc.) are extremely variable. To compound this variability, some populations of some species are polymorphic, and some exhibit sexual dimorphism in body size. (Carleton and Musser, 1984; Hubbard, 1972; Nowak, 1999)

  • Sexual Dimorphism
  • sexes alike
  • female larger
  • male larger

Reproduction

Muroids have monogamous, polygynous, and polygynandrous mating systems. Most commonly, they are polygynandrous, with males and females each having multiple mates over the course of a breeding period. (Nowak, 1999)

Given the incredible diversity of this group, it is nearly impossible to generalize about the life-history characteristics of its members. The "typical" muroid species is characterized by a "fast" life: high reproductive output at an early age and a high mortality rate. The high reproductive output is made possible in many species by a postpartum estrus, which allows females to become pregnant again immediately after giving birth. Sometimes implantation of the embryos is delayed until after a female stops lactating, and in some species, the act of mating itself induces ovulation. (Carleton and Musser, 1984; Nowak, 1999)

Muroid mothers, like all female mammals, provide their young with milk until the young can eat solid food. Many muroid females build nests in which they raise and care for their young, which range from altricial to precocial. Male parental care is rare in this group, but it does occur in a few species. In most muroid species, the young disperse soon after they are weaned, but in a few, they stay with their parents for more than one breeding season. (Gubernick and Teferi, 2000; Schradin and Pillay, 2003; Sommer, 2000)

  • Parental Investment
  • altricial
  • precocial
  • pre-fertilization
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • male
      • female
  • post-independence association with parents

Lifespan/Longevity

Most muroids face a large array of predators and put all of their energy into a high reproductive output early in life, and therefore do not live more than a year or two in the wild. Captivity often extends the lifespan by several years. (Nowak, 1999)

Behavior

Muroid rodents run the gamut of behaviors, from nocturnal to diurnal, from arboreal to fossorial, from solitary to colonial. There are muroid rodents specialized for climbing, burrowing, swimming, and hopping, and there are those that are generalists and are fairly good at doing all of the above. (Nowak, 1999)

Communication and Perception

To avoid the many predators that they face, and to find food and mates, muroid rodents have evolved acute visual, acoustic, tactile, and chemical senses, but the relative importance of these for each species varies widely. The means by which muroid rodents communicate also varies between species. A common theme in mammalian communication is the use of pheromones, which are used widely by muroid rodents to send and receive signals about an individual's status. In addition, some communicate using sounds (including ultrasounds) or vibrations. (Ehret, 2005; Johnston, 2003; Nowak, 1999; Smith, 1972; Thompson, et al., 2004)

Food Habits

Muroid food habits range from true omnivores to generalist herbivores to specialists on insects, earthworms, subterranean fungi, and even aquatic invertebrates. Many species, especially herbivorous species, store their surplus food for later use. (Nowak, 1999)

Predation

Muroid rodents, as a group, have predators belonging to nearly every class of vertebrates, including birds and other reptiles, amphibians, fish, and other mammals. To avoid their numerous predators, muroid rodents have evolved strategies of hiding, running, swimming, hopping, climbing, and biting. There are even those that, when grabbed, lose their tails and buy themselves enough time to escape. One unique species, Lophiomys imhausi, is aposematic, exudes a musky odor, and may be a porcupine mimic through the use of stiff, erectile hairs. (Carleton and Musser, 1984; Cochran and Cochran, 1999; Nowak, 1999; Shargal, et al., 1999)

Ecosystem Roles

Some muroid rodents may be essential ("keystone") species in maintaining the health of forests, through their role in spreading mycorrhizal fungi or dispersing seeds. Others affect the rate of forest succession by preying on tree seedlings. Some species are important pollinators. Others dig tunnels, and in doing so, create habitat for other species and aerate the soil. Many species are a vital food source for a wide range of predators, and muroids as a group support many different kinds of parasites, such as ticks and mites, fleas, lice, bot flies, nematodes, tapeworms, and trypanosomes. Finally, a few muroid species are commensal with humans, inhabiting cities and towns and relying on human-produced waste to survive. (Johnson, et al., 2001; Manson, et al., 2001; Roberts and Janovy, Jr, 2000; Zhang, et al., 2003)

Species Used as Host
Commensal/Parasitic Species

Economic Importance for Humans: Positive

Many muroid species are beneficial to man. Some are important biological controls of pest insects. Some are popular pets. Others are hunted for their meat, their skins, or their bones (which may be used in traditional medicine). And a few species play an essential role in medical research that has been enormously beneficial to human populations. (Nowak, 1999; Zhang, et al., 2003)

Economic Importance for Humans: Negative

Some muroid species cause millions of dollars of damage to agricultural lands and stored foods. Several are pests that destroy household goods, cause structural damage, and even start fires by gnawing on electrical wires. Others are the vectors or reservoirs of a number of diseases that have periodically devasted human populations (and continue to do so). (Nowak, 1999)

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

Conservation Status

Almost 26% of muroid species are on the IUCN Red List of Threatened Species. This includes 32 critically endangered species and 70 endangered species. Many of the threatened muroid species are endemic, and their restricted ranges render them especially vulnerable to habitat destruction and fragmentation, the two main threats to this and many other taxonomic groups. Few steps have been taken to save threatened muroid species; they are not particularly charismatic or popular with the public and in many cases there is simply not enough known about them to know where to begin. (IUCN, 2004)

  • IUCN Red List [Link]
    Not Evaluated

Contributors

Phil Myers (author), Museum of Zoology, University of Michigan-Ann Arbor, Allison Poor (author), University of Michigan-Ann Arbor, Tanya Dewey (editor), Animal Diversity Web.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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Ethiopian

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

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Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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Neotropical

living in the southern part of the New World. In other words, Central and South America.

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Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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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.

aposematic

having coloration that serves a protective function for the animal, usually used to refer to animals with colors that warn predators of their toxicity. For example: animals with bright red or yellow coloration are often toxic or distasteful.

arboreal

Referring to an animal that lives in trees; tree-climbing.

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.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

carnivore

an animal that mainly eats meat

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

chemical

uses smells or other chemicals to communicate

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

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.

delayed implantation

in mammals, a condition in which a fertilized egg reaches the uterus but delays its implantation in the uterine lining, sometimes for several months.

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

drug

a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease

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.

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

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.

holarctic

a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

World Map

Found in northern North America and northern Europe or Asia.

induced ovulation

ovulation is stimulated by the act of copulation (does not occur spontaneously)

insectivore

An animal that eats mainly insects or spiders.

internal fertilization

fertilization takes place within the female's body

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

island endemic

animals that live only on an island or set of islands.

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).

keystone species

a species whose presence or absence strongly affects populations of other species in that area such that the extirpation of the keystone species in an area will result in the ultimate extirpation of many more species in that area (Example: sea otter).

marsh

marshes are wetland areas often dominated by grasses and reeds.

migratory

makes seasonal movements between breeding and wintering grounds

molluscivore

eats mollusks, members of Phylum Mollusca

monogamous

Having one mate at a time.

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.

mycophage

an animal that mainly eats fungus

natatorial

specialized for swimming

native range

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

nocturnal

active during the night

nomadic

generally wanders from place to place, usually within a well-defined range.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

omnivore

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

oriental

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

World Map

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

piscivore

an animal that mainly eats fish

polar

the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

polygynous

having more than one female as a mate at one time

polymorphic

"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

riparian

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

saltatorial

specialized for leaping or bounding locomotion; jumps or hops.

scavenger

an animal that mainly eats dead animals

scent marks

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

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

semelparous

offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.

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.

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"

suburban

living in residential areas on the outskirts of large cities or towns.

swamp

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

tactile

uses touch to communicate

taiga

Coniferous or boreal forest, located in a band across northern North America, Europe, and Asia. This terrestrial biome also occurs at high elevations. Long, cold winters and short, wet summers. Few species of trees are present; these are primarily conifers that grow in dense stands with little undergrowth. Some deciduous trees also may be present.

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.

tundra

A terrestrial biome with low, shrubby or mat-like vegetation found at extremely high latitudes or elevations, near the limit of plant growth. Soils usually subject to permafrost. Plant diversity is typically low and the growing season is short.

ultrasound

uses sound above the range of human hearing for either navigation or communication or both

urban

living in cities and large towns, landscapes dominated by human structures and activity.

vibrations

movements of a hard surface that are produced by animals as signals to others

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

Carleton, M. 1984. Introduction to rodents. Pp. 255-265 in S Anderson, J Jones Jr., eds. Orders and Families of Recent Mammals of the World. New York: John Wiley and Sons.

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.

Cochran, P., J. Cochran. 1999. Predation on a Meadow Jumping Mouse, Zapus hudsonius, and a House Mouse, Mus musculus, by Brown Trout, Salmo trutta. Canadian Field-Naturalist, 113 (4): 684-685.

Ehret, G. 2005. Infant rodent ultrasounds - A gate to the understanding of sound. Behavior Genetics, 35(1): 19-29.

Gubernick, D., T. Teferi. 2000. Adaptive significance of male parental care in a monogamous mammal. Proceedings of the Royal Society of London, 267 (1439): 147-150.

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

IUCN, 2004. "IUCN Red List of Threatened Species" (On-line). Accessed May 16, 2005 at www.redlist.org.

Johnson, S., A. Pauw, J. Midgley. 2001. Rodent pollination in the African lily Massonia depressa (Hyacinthaceae). American Journal of Botany, 88(10): 1768-1773.

Johnston, R. 2003. Chemical communication in rodents: From pheromones to individual recognition. Journal of Mammalogy, 84 (4): 1141-1162.

Manson, R., R. Ostfeld, C. Canham. 2001. Long-term effects of rodent herbivores on tree invasion dynamics along forest-field edges. Ecology, 82 (12): 3320-3329.

Musser, G., M. Carleton. 2005. Superfamily Muroidea. D Wilson, D Reeder, eds. Mammal Species of the World. 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, DC: Smithsonian Institution Press.

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

Roberts, L., J. Janovy, Jr. 2000. Foundations of Parasitology. New York: McGraw-Hill.

Schradin, C., N. Pillay. 2003. Paternal care in the social and diurnal striped mouse (Rhabdomys pumilio): laboratory and field evidence. Journal of Comparative Psychology, 117 (3): 317-324.

Shargal, E., L. Rath-Wolfson, N. Kronfeld, T. Dayan. 1999. Ecological and histological aspects of tail loss in spiny mice (Rodentia: Muridae, Acomys) with a review of its occurrence in rodents. Journal of Zoology, 249: 187-193.

Smith, J. 1972. Sound production by infant Peromyscus maniculatus (Rodentia:Myomorpha). Journal of Zoology, 168: 369-379.

Sommer, S. 2000. Sex-specific predation on a monogamous rat, Hypogeomys antimena (Muridae: Nesomyinae). Animal Behavior, 59: 1087-1094.

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.

Thompson, R., B. Robertson, A. Napier, K. Wekesa. 2004. Sex-specific responses to urinary chemicals by the mouse vomeronasal organ. Chemical Senses, 29(9): 749-754.

Zhang, Y., Z. Zhang, J. Liu. 2003. Burrowing rodents as ecosystem engineers: the ecology and management of plateau zokors Myospalax fontanierii in alpine meadow ecosystems on the Tibetan Plateau. Mammal Review, 33(3): 284-294.

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