The wood lemming (''Myopus schisticolor'') is a species of

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are na ...

in the family

Cricetidae The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, muskrats, and New World rats and mice. At almost 608 species, it is the second-largest family of mammals, and has m ...

. It belongs to the rodent

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...

Arvicolinae The Arvicolinae are a subfamily of rodents that includes the voles, lemmings, and muskrats. They are most closely related to the other subfamilies in the Cricetidae (comprising the hamsters and New World rats and mice). Some authorities place ...

, so is a relative of the

vole Voles are small rodents that are relatives of lemmings and hamsters, but with a stouter body; a longer, hairy tail; a slightly rounder head; smaller eyes and ears; and differently formed molars (high-crowned with angular cusps instead of low-c ...

lemming A lemming is a small rodent, usually found in or near the Arctic in tundra biomes. Lemmings form the subfamily Arvicolinae (also known as Microtinae) together with voles and muskrats, which form part of the superfamily Muroidea, which also include ...

s, and

muskrat The muskrat (''Ondatra zibethicus'') is a medium-sized semiaquatic rodent native to North America and an introduced species in parts of Europe, Asia, and South America. The muskrat is found in wetlands over a wide range of climates and habitat ...

s. It is found in the taiga biome of

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

Estonia Estonia, formally the Republic of Estonia, is a country by the Baltic Sea in Northern Europe. It is bordered to the north by the Gulf of Finland across from Finland, to the west by the sea across from Sweden, to the south by Latvia, a ...

Finland Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of B ...

Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million, ...

Norway Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...

Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...

, and

Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...

Sex determination

Wood lemmings produce about three times as many female as male offspring. This is due to an unusual genetic system where they have two different types of X

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

s, the normal X and a mutated X*. Females with that mutation on their X*-chromosome inhibit the male determining effect of the Y chromosome. This leads to three genetic types of females: XX, X*X and X*Y and one genetic type of males XY. The X*Y females are fertile, but only produce X* ova, which means they only produce female offspring. It is not fully known the extent to which nature balances out the differences in the adult population, but sampling studies seem to suggest males do make up as little as 25% of the population at equilibrium. Females with abnormal genotype (XO, XXY, X*YY) occur regularly. The high female sex ratio may be an adaptation against local mate competition and inbreeding during population low points.

Population dynamics

The population density of lemmings shows extreme peaks interspersed by years of very low densities. In peak years, wood lemmings migrate from overpopulated areas to areas of low population density. The migration usually begins around the end of July and ends in early October. The migratory distances are typically quite short, ranging a few kilometers at most, with no specific direction.Eskelinen, Olavi (2004)
"Studies on the ecology of the wood lemming, Myopus schisticolor"
University of Joensuu, PhD Dissertations in Biology (Joensuu) p. 24 If geographical features do not allow the animals to disperse evenly during their migration, then thousands of lemmings can be seen on their migration. This migratory behavior was exaggerated in popular stories about lemmings; innumerable numbers dash down the hillsides and fall down over rocks into the sea, only to drown. However, such stories of mass suicides in lemmings are mere legends. The size of home ranges between male and female wood lemmings varies greatly. Male home ranges (>2000 m²) are five to seven times larger than those of females.

Diet

The diet of the wood lemming consists mostly of moss. The most commonly consumed species of moss are ''

Dicranum ''Dicranum'' is a genus of mosses, also called wind-blown mosses or fork mosses. These mosses form in densely packed clumps. Stems may fork, but do not branch. In general, upright stems will be single but packed together. ''Dicranum'' is distrib ...

'', ''

Polytrichum ''Polytrichum'' is a genus of mosses — commonly called haircap moss or hair moss — which contains approximately 70 species that cover a cosmopolitan distribution. The genus ''Polytrichum'' has a number of closely related sporophytic character ...

'', '' Ptilium'', and ''Pleurozium'', with ''Dicranum'' being the moss of choice. In Northern Finland, ''Dicranum'' spp. made up the majority of the lemmings' winter food supply. These mosses are thought to be preferred because of their usability and relatively high nitrogen content. Lemmings will also eat some grass species, such as ''

Deschampsia ''Deschampsia'' is a genus of plants in the grass family, commonly known as hair grass or tussock grass. The genus is widespread across many countries.

'', as well as the leaves and stems of ''

Vaccinium ''Vaccinium'' is a common and widespread genus of shrubs or dwarf shrubs in the heath family (Ericaceae). The fruits of many species are eaten by humans and some are of commercial importance, including the cranberry, blueberry, bilberry (whort ...

'' spp.

Habitat

Wood lemmings can be found in areas from southern

Kamchatka The Kamchatka Peninsula (russian: полуостров Камчатка, Poluostrov Kamchatka, ) is a peninsula in the Russian Far East, with an area of about . The Pacific Ocean and the Sea of Okhotsk make up the peninsula's eastern and wes ...

(taiga area of Eurasia). Their ideal habitat is a spruce forest with thick, copious moss cover. Lemmings gravitate towards areas with abundant cover from predators, i.e., holes provided by decomposed trees, stumps, and mossy rock. In the winter, wood lemmings seek out drier areas than summer.

Activity

Metabolism

The wood lemming is well adapted to live in cold climates due to its high thermogenic capacity, thermal insulation, and nonshivering thermogenesis. Compared to other

s, lemmings drink greater amounts of water, which may be why they seek moister areas in the spring and summer. On average, males travel four to 12 times farther than females.

Reproduction

Breeding and reproduction usually happen in the winter months. Females reach sexual maturity at the age of 22–40 days, while males reach sexual maturity beginning around 44 days old and not before they reach a body weight of 20 grams. Females are able to have two or three litters per year. Litter sizes usually range from three to seven young. The approximate life expectancy of a wood lemming is less than one year.

References

{{Taxonbar, from=Q665347 Lemmini Fauna of Scandinavia Mammals described in 1844 Taxa named by Wilhelm Lilljeborg Taxonomy articles created by Polbot