Wood lemming
Myopus schisticolor
— Where the name comes from
Myopus puts together mŷs and poús, “mouse-foot”. Schisticolor is “slate-coloured”, from the Greek schistós, the stone that splits into sheets: the uniform dark grey of the coat, with a single rust patch on the rump. It is the lemming that lives not in the tundra but in the moss forest, and the colour says so.
— Facts
- Group
- Mammals · Mammalia
- Order
- Rodents
- Habitat
- Damp taiga with a continuous carpet of moss
- Range
- From Norway to eastern Siberia and Mongolia
- Size
- 8–11 cm of body, tail 1.5–2 cm, 20–45 g
- Diet
- Almost exclusively mosses
- Lifespan
- 2 years
— Characteristics
- 01
It eats moss, food so poor that it must swallow its own weight in it every day.
- 02
It tunnels inside the carpet of moss, not in the soil.
- 03
In its populations the females outnumber the males two to one.
— What sets it apart
It has broken one of the firmest rules in mammal biology: in this species there are females with XY chromosomes. A mutation on the X chromosome blocks the masculinising signal, and those females — fertile, and mothers of daughters only — shift the sex ratio towards females, that is they raise the number of offspring per group. It is one of the very few known cases in which sex determination in mammals has been rewritten by evolution, and it is studied to understand how rigid the XY system really is.
