Myopus
| Wood lemming | |
|---|---|
 |
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| Wood lemming camouflaged on the forest floor | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Rodentia |
| Family: | Cricetidae |
| Subfamily: | Arvicolinae |
| Tribe: | Lemmini |
| Genus: |
Myopus Miller, 1910 |
| Species: | M. schisticolor |
| Binomial name | |
|
Myopus schisticolor (Lilljeborg, 1844) |
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The wood lemming (Myopus schisticolor) is a species of rodents in the family Cricetidae. It belongs to the Arvicolinae subfamily of rodents, so is a relative of the voles, lemmings, and muskrats. It is found in the taiga biome of China, Finland, Mongolia, Norway, Russia, and Sweden.
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 chromosomes, 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.
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. 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.
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Wikipedia