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MurinaeOld World rats and mice

By Allison Poor

Diversity

Murinae, the Old World rats and mice, is the largest subfamily of muroid rodents. There are an astonishingly diverse 561 species in this subfamily, which are divided among 126 genera in 29 divisions. (Musser and Carleton, 2005)

Geographic Range

Rats and mice are native to the Ethiopian, Palearctic, and Oriental regions, including Africa, the Arabian Peninsula, Europe, the Middle East, India, China, Taiwan, Korea, Japan, the Indo-Malayan region, the Philippines, New Guinea, Australia, and Tasmania. In addition, murines have been introduced around the world by humans, and now have a virtually cosmopolitan distribution. (Carleton and Musser, 1984)

Habitat

Murines occupy a wide variety of boreal, temperate, subtropical, and tropical habitats, including: coniferous and deciduous forests, subtropical broadleaf forests, tropical rainforests, monsoon forests, savannahs, steppes, grasslands, scrub forests, alpine meadows, deserts, rocky outcrops, river valleys, marshes, swamps, lakes, rivers, streams, agricultural fields, cities, and towns. Murines span a greater elevational range than any other muroid subfamily; they have been found in high mountains at more than 4,000 meters, and in mine shafts more than 500 meters below the earth's surface. (Carleton and Musser, 1984; Nowak, 1999)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

Physical Description

There is an incredibly diverse range of body types in this subfamily. Murines can be shrew-like, gerbil-like, vole-like, gopher-like, squirrel-like, mouse-like, and rat-like, with many variations on each body plan. Some are small and gracile, like tiny African pygmy mice (Mus minutoides), which are less than 9 cm long and weigh in at under 5 grams, and some are large and robust, like southern Luzon giant cloud rats (Phloeomys cumingi), which grow to over 48 cm long and weigh over 2 kg. Murines usually have prominent ears, and their tails can be long or short. The fur is smooth and silky, woolly, short and velvety, coarse and thin, or spiny. The tail is naked to bushy, and is prehensile or semi-prehensile in some species. The ears can be either scantily-haired or furry, and the soles of the feet are hairless. The fur may be various shades of brown and gray on the dorsal surface, and is usually white, buff, or grayish on the ventral surface. Some species have dorsal stripes. The tail is usually monocolored but is sharply bicolored in some. Polymorphism is present in some species, with two or more color morphs living in sympatry. Male murines have large ventral sebaceous glands. There are no cheek pouches. The feet are cursorially adapted in most, and can be either short and wide or long and narrow. In some species, the feet are webbed. The front feet each have four digits that bear claws plus a stubby thumb bearing a nail. All five digits on each hind foot bear claws in most genera. Some arboreal species have semiopposable thumbs.

The dental formula is 1/1, 0/0, 0/0, 3/3 = 16 in most murine genera. The incisors can be opisthodont, orthodont, or proodont. Most have ungrooved incisors. The molars are rooted and are not evergrowing. The molars range from brachydont to hypsodont, and the third molars are always smaller than the first and second molars. Most murines have three lingual cusps on the upper molars, giving a triserial cusp arrangement; there is always at least an anterolingual cusp on the second upper molars. In addition, the lower molars usually have labial cusplets. Murines vary widely in skull characteristics, and the diversity is so great that no synapomorphies of the skull can be identified, except of the lack of a sphenofrontal foramen or squamosoalisphenoid groove. A skeletal characteristic that all murine genera share is the presence of a prominent neural spine on the second thoracic vertebra. Diploid chromosome numbers for murines range from 25 to 68. (Carleton and Musser, 1984; Hubbard, 1972; Nowak, 1999)

Reproduction

Most murines have a polygynandrous mating system, with each male and female only associating for the brief time required for copulation and each individual having multiple mates. A few species are monogamous, at least within one breeding season, and males stay with their mates and help to raise their young. (Nowak, 1999)

Many murines are prolific breeders. Females of some species are able to breed when they are just a few weeks old and give birth to litters of 7, 10, or even 13 young after a gestation that lasts less than a month. Many experience a postpartum estrus so that they give birth again shortly after weaning the first litter, and they may have ten or more litters per year. This incredible reproductive potential is, in part, what contributes to the success of this subfamily. However, most murines, while more prolific than many mammals, have a somewhat lower reproductive output. Litter sizes of one to four young are common for many species, and the young reach sexual maturity after three months. Many are seasonal breeders, and as a result, they produce three or four litters per year (instead of nine or ten) when the climate is favorable. (Nowak, 1999)

Female murines, like all mammals, provide their young with milk before the young are able to eat solid food. Many murines build nests--the size, shape and location of which varies among species--in which they raise their young. Yet females of other species simply allow their babies to clamp on to their teats and then carry their young around with them. The time to weaning is relatively short, as young murines grow and develop quickly. Both altricial and precocial murine species are known. Male parental care is rare, but not unheard of, in this group. For example, male four-striped grass mice (Rhabdomys pumilio) spend just as much time in the nest with their offspring as females do, grooming their young and retrieving them if they stray (Schradin and Pillay 2003). Most murine young do not associate with their parents for long, leaving to seek their own territories and mates shortly after they are weaned. (Nowak, 1999; Schradin and Pillay, 2003)

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

Lifespan/Longevity

Murines usually do not live more than a few months in the wild, and those that do rarely live to be three years old. In captivity, however, some murines may live nearly a decade. (Nowak, 1999)

Behavior

Behavioral characteristics, like other traits, vary widely in the subfamily Murinae. Because they fill countless niches in a wide array of habitats, murines have also evolved a mind-boggling array of behaviors. There are murines that are terrestrial, arboreal, and aquatic, and those that are nocturnal, diurnal, and crepuscular. Some are territorial and solitary, others are social or colonial. Some have strict dominance hierarchies. Some are sedentary, others are migratory. Most murines have a regular spot where they seek shelter, which may be a nest in a tree or shrub, a burrow, a hollow tree, a crevice between two rocks, a crack in the wall of a house, or hundreds of other possibilities. The majority are cursorial, but there are murines that are specialized for hopping, climbing, swimming, and locomoting in all of these ways. (Nowak, 1999)

Communication and Perception

Murines perceive the world using vision, hearing, touch, smell, and taste. The relative importance of these senses varies among species and relates to each species' lifestyle. For example, murines that forage under the cover of darkness might rely more on smell, touch, and hearing than on vision, while the opposite might be true for diurnal murines. The range of murine perception often surpasses that of humans; for example, some murines can hear ultrasounds, as youngsters that have been separated from their mothers often emit ultrasonic calls, to which mothers quickly respond (Ehret 2005). In general, murine communication involves a combination of chemical, tactile, visual, and auditory cues--the relative importance of which, again, varies among species. As is the case for many mammals, pheromones play a large role in intraspecific interactions in murines, allowing individuals to attract and locate mates, assess each other's status in the dominance hierarchy, or to synchronize their reproductive cycles (Thompson et al. 2004). Males of many territorial species demarcate their boundaries by scent-marking with their large ventral sebaceous glands. (Carleton and Musser, 1984; Ehret, 2005; Nowak, 1999; Thompson, et al., 2004)

Food Habits

As a group, murines consume an astonishing array of food items, including (but not limited to) roots, grains, leaves, shoots, seeds, berries, nuts, fungi, fruits, insects, earthworms, arachnids, fish, small birds and eggs, turtles, lizards, frogs, mussels, carrion, and even household items such as glue, paste, and soap. Individual murine species range from dietary generalists that will eat just about anything to specialist herbivores and specialist carnivores. Many murine species cache their food in burrows or crevices for later use. (Nowak, 1999)

Predation

Murines are a food source for a myriad of predators belonging to almost every extant vertebrate class, including mammalian carnivores (such as foxes, cats, and weasels), birds of prey (such as hawks, eagles, and owls), non-bird reptiles (such as snakes and large lizards), amphibians (such as large frogs and toads), and even large fish (Cochran and Cochran 1999).

Because they are up against such a large array of predators, murines have evolved numerous strategies for avoiding being eaten. Many are only active after dark, when diurnal predators (like snakes and hawks) may have a difficult time hunting them. Murines often seek refuge in burrows or crevices that are too small for predators to enter. In addition, many rely on their versatility to escape predators, and can run, leap, climb or swim in a pinch, even if they do not normally do so. Murines tend to have neutral-colored coats that blend in with the natural backgrounds of their habitats, affording them some degree of camouflage. Finally, like most wild mammals, murines often bite viciously when attacked and may inflict enough surprise or damage that predators release them. (Cochran and Cochran, 1999; Nowak, 1999)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Murines are essential components of many ecosystems. They have roles as seed dispersers, pollinators (Johnson et al. 2001), predators, and/or prey. Not all ecosystem roles are positive, however. Some murine species have been introduced to areas where they were previously absent, and they have devastated ecosystems by outcompeting or feeding on native wildlife. A few murine species have developed a commensal relationship with humans, and, especially in urban areas, rely on human-produced waste to survive. In turn, various parasites use murines as hosts, including ticks and mites, fleas, lice, bot flies, nematodes, tapeworms, and trypanosomes. (Johnson, et al., 2001; Nowak, 1999; Roberts and Janovy Jr., 2000)

Species Used as Host
Commensal/Parasitic Species

Economic Importance for Humans: Positive

Murines have an immense positive economic impact on human populations. First, some murine species are kept as pets, and some are sold by pet stores as food for other types of pets, such as snakes and lizards. Also, murines have been used as model organisms in laboratories for years, and their contribution to scientific and medical research cannot be overstated. Throughout history, humans have resorted to eating rats during times of famine to avoid starvation (although this practice probably contributes greatly to the spread of disease), and some murine species are prized as food or for their pelts and hunted regularly. (Nowak, 1999)

  • Positive Impacts
  • pet trade
  • food
  • body parts are source of valuable material
  • research and education

Economic Importance for Humans: Negative

Although most murines have no direct impact whatsover on humans, those that do cause enough damage and suffering to give the entire group a bad name. Every year, rats and mice cause billions of dollars worth of property damage worldwide by gnawing on structures and on electrical wires, damaging buildings and starting fires. They are common household pests, raiding kitchens and granaries and causing much crop damage when they are abundant. In addition, they are carriers of numerous human diseases, from mild cases of food poisoning, to murine typhus and the highly deadly plague, which has had an enormous impact on human history, wiping out a quarter of Europe's population in a single 14th century epidemic. (Nowak, 1999; Roberts and Janovy Jr., 2000)

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

Conservation Status

The subfamily Murinae contains some of the most common species on Earth--the house mouse (Mus musculus) and Norway rat (Rattus norvegicus) come to mind--but it also contains a large number of species with small populations and restricted ranges. In fact, 41% of the species in this subfamily are on the IUCN's Red List of threatened species. This includes 20 critically endangered species, 41 endangered species, 66 vulnerable species, 13 near threatened species, 53 lower risk species, and 25 species that cannot be classified due to lack of information. Another 13 species are presumed to have gone extinct in recent years. The largest threat to most of these species is also the largest threat to the Earth's biodiversity overall: human-induced habitat loss and degradation. Specific conservation measures have not been enacted for many species, but for some, research is underway to better understand their ecology and for a few, protected areas have been established to offset the effects of habitat loss. (IUCN, 2004)

  • IUCN Red List [Link]
    Not Evaluated

Other Comments

The earliest murine fossils are from the middle Miocene of northern Pakistan. The group is thought to have evolved in southern Asia and from there expanded outward into other parts of the Old World. (Carleton and Musser, 1984)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

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

Glossary

Australian

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

World Map

Ethiopian

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

World Map

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.

World Map

Neotropical

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

World Map

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.

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.

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

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.

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.

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.

insectivore

An animal that eats mainly insects or spiders.

introduced

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

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

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

polygynandrous

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

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

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.

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.

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., 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): 684-684.

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

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 08, 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.

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

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.

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. Baltimore and London: The Johns Hopkins University 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.

Steppan, S. 2005. "Murinae" (On-line). Tree of Life Web Project. Accessed May 31, 2005 at http://tolweb.org/tree?group=Murinae&contgroup=Muroidea.

Steppan, S. 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.

Watts, C., P. Baverstock. 1994. Evolution in some South-east Asian Murinae (Rodentia), as assessed by microcomplement fixation of albumin, and their relationship to Australian murines. Australian Journal of Zoology, 42 (6): 711-722.

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