Arvicolinae
lemmings and voles

Arvicolinae is a large subfamily of cricetid rodents that are fairly uniform in appearance but diverse in their habits. There are 151 species in this family, in 28 genera. The genera are divided among 10 tribes. (Musser and Carleton, 2005; Nowak, 1999)

The subfamily Arvicolinae has a Holarctic distribution. Arvicolines are found throughout North America from Guatemala northward, throughout Eurasia, in Japan, Taiwan, southwestern China, northern India, the Middle East including Asia Minor, and in Africa to Libya. (Carleton and Musser, 1984)

Arvicolines inhabit a wide range of habitats within temperate, boreal, arctic, and montane biomes. These habitats include: dry and wet deciduous and coniferous forests, brushy or rocky mountain slopes, alpine meadows, prairies, steppes, agricultural fields, semidesert, cloud forests, tundra, riparian zones, lakes, marshes, and sphagnum bogs. (Carleton and Musser, 1984; Nowak, 1999)

Arvicolines are medium to large muroid rodents, ranging in head and body length from 70 mm to over 300 mm, and ranging in tail length from 5 to 295 mm. The tail is always shorter than the head and body. Arvicolines weigh anywhere from 15 grams to over 1.8 kg. They have stout bodies with small, rounded ears, blunt snouts, and short legs. The eyes are relatively large. Adult males, and sometimes females, have large sebaceous glands on the rump, hips, flanks, or tail region. Most arvicolines have cursorially adapted feet, and some have long claws for digging. Arvicoline fur is usually thick and ranges from long to short and from smooth to harsh. In some species the texture changes with the seasons, becoming shorter and thinning out in the summer. The tail is covered with fur in most species, and sometimes bears a terminal tuft. The fur on the dorsal surface of arvicolines can be various shades of brown or gray, and in some species it has a distinct red or yellow cast. The fur on the ventral surface is pale brown, white, cream, buff, yellowish, or gray. Some species have bicolored tails that are darker above than below. There are polymorphic arvicoline populations, with two or more color morphs living in the same area.

The dental formula of arvicolines is 1/1, 0/0, 0/0, 3/3 = 16. The incisors may be orthodont, opisthodont, or proodont, and the molars may either be rooted or evergrowing. The molars bear a prismatic enamel pattern. Arvicolines have relatively large skulls. The squamosomastoid foramen is always present, and most have a stapedial foramen as well. The palatine process of the maxillary and the palatine are thickened dorsoventrally, in conjunction with the molars' large alveolar capsules. There are usually longitudinal furrows and ridges, as well as tiny perforations, in the bony palate. There are 13 thoracic vertebrae and six lumber vertebrae in the arvicoline vertebral column.

Arvicolines have stomachs that are either one- or two-chambered, and their large intestines and ceca are extremely complex. However, the small intestine is quite short. There is no supraorbital branch of the stapedial artery; instead, the infraorbital branch supplies blood to the orbits. Arvicolines have a diploid chromosome number between 18 and 62. (Carleton and Musser, 1984; Nowak, 1999)

Most arvicolines are promiscuous, with males and females both having multiple mates. In some species, a copulatory plug forms and seals the female's reproductive tract, preventing subsequent males from successfully fertilizing the female's eggs. However, a few species, such as muskrats and prairie voles, live in monogamous pairs and share the responsibility of raising young. In fact, in captivity it has been shown that prairie voles stay with their parents for more than one breeding period and help raise their younger siblings (Gruder-Adams and Getz 1985). (Carleton and Musser, 1984; Gruder-Adams and Getz, 1985; Nowak, 1999)

Many arvicolines are capable of breeding year round, and some species even give birth to litters under snow cover. Others concentrate their reproductive efforts during the warmer months and breed from spring to autumn, with a peak in breeding occurring from late spring to early summer. In some species, ovulation is not spontaneous; rather, it is induced by the act of mating. Females are polyestrus, giving birth to anywhere from 1 to 7 litters per year. They often become impregnated again as soon as they give birth, due to a postpartum estrus. However, implantation of the embryo is delayed in some species while the female is lactating. Gestation from the time the embryo implants is 16 to 30 days. Litter sizes average 3 to 7 young, but some females have as few as one and as many as 13 young in a litter. The young are relatively precocial and develop rapidly, opening their eyes at 8 to 16 days and becoming weaned and independent at 12 to 35 days. Females often breed in the year that they are born, becoming sexually mature as early as 14 days. Males mature somewhat later than females. (Carleton and Musser, 1984; Nowak, 1999)

Most female arvicolines invest little in each individual offspring, instead employing a strategy of high reproductive output. They build nests in which they rear their litters and nurse their relatively precocial young for 12 to 35 days. Often females become highly aggressive when nursing, fiercely defending their litters against intruding males. Male parental care occurs in this group, with males of some species brooding the young in the nest or retrieving them when they wander away. Also, care of youngsters by older siblings has been reported for arvicolines kept in captivity (Gruder-Adams and Getz 1985). (Gruder-Adams and Getz, 1985; Nowak, 1999)

Most arvicolines only live for a few months in the wild. Captivity often extends the life span by several years. (Nowak, 1999)

Arvicolines, as a group, display a wide range of lifestyles. Some are terrestrial, some are semi or fully aquatic, some are arborial, and some are fossorial. They are adapted for cursorial or natatorial locomotion. Most are active at any time of the day or night, some are strictly nocturnal, and a few are diurnal. They are active throughout the year. Arvicolines build nests in underground burrows, depressions in the ground, tree holes, tree branches, or under rocks or logs. Some maintain complex tunnel systems underground, through the grass, or under the snow. Underground tunnel systems often have multiple entrances and consist of a nest chamber and adjacent chambers for food storage and defecation.

Arvicolines range in social habits from solitary, aggressive, and territorial to gregarious and colonial. In some species, population densities become extremely high in certain years, prompting mass migrations. These population increases are often cyclical in nature, occuring at regular intervals. (Carleton and Musser, 1984; Nowak, 1999)

Arvicolines are able to perceive tactile, visual, auditory, and chemical signals. Chemical signals are especially important for communication. Males, and sometimes females, mark their territories with secretions from their sebaceous flank glands. Also, some arvicolines are highly vocal and make a variety of chirping and chattering noises when disturbed or when engaged in a conflict with a conspecific. (Nowak, 1999)

Arvicolines are primarily herbivorous, though some species are omnivorous. They consume leaves, grasses, forbs, roots, bulbs, bark, twigs, stems, pine needles, berries, nuts, seeds, lichen, fungi, insects, crayfish, mussels, and small fish. Some species cache food in their nests or burrows for use during times of shortage. (Carleton and Musser, 1984; Nowak, 1999)

Hawks, owls, snakes, and small mammalian carnivores are the main predators of arvicolines. Arvicolines can be quite vicious, gnashing their teeth and biting when threatened. Also, their neutral-colored fur probably keeps them somewhat camouflaged. (Carleton and Musser, 1984; Nowak, 1999)

Arvicolines are primary and secondary consumers, and they provide a staple food source for many other species. The fossorial species turn over earth when they dig, and therefore may help to aerate the soil. Arvicolines are important for seed dispersal, and they impact forest regeneration by preying on tree seedlings (Manson et al. 2001). Because of their important role in forest dynamics, some are considered keystone species. Finally, because of their high reproductive output and cyclical boom and bust cycles in population numbers, the population dynamics of arvicolines often influences heavily the population dynamics of predators such as snowy owls and Canada lynx, and plant community composition through their grazing activity. (Manson, et al., 2001; Nowak, 1999)

Some arvicolines eat large quantities of insect larvae and therefore act as important controls on pest species. Others are hunted for their pelts or for food. (Nowak, 1999)

Some arvicolines carry diseases such as tularemia. Those that dwell in agricultural areas sometimes damage crops. (Nowak, 1999)

In the subfamily Arvicolinae, the IUCN lists 23 lower risk species, 1 near threatened species (wood lemming, Myopus schisticolor), 4 vulnerable species (Central Kashmir vole, Alticola montosa, Mexican vole, Microtus mexicanus, Taiwan vole, Volemys kikuchii, and Japanese red-backed vole, Phaulomys andersoni), 2 endangered species (Alai mole vole, Ellobius alaicus and Baluchistan vole, Microtus kermanensis), 3 critically endangered species (Wrangel lemming, Dicrostonyx vinogradovi, Evorsk vole, Microtus evoronensis, and Muisk vole, Microtus mujanensis), and 7 species lacking sufficient data to be ranked. Many arvicolines have restricted ranges, rendering them vulnerable to habitat loss. (IUCN, 2004)

The earliest undisputed arvicoline fossils are from the early Pliocene of northwest Asia, Europe, and North America. It is thought that arvicolines spread into southern Asia in the late Pliocene. (Musser and Carleton, 2005)