Norway lemmings appeared on the scene only 35,000 years ago. PHOTO: LOVE DALÉN
Norway lemmings are a relatively new species, which arose during the last ice age.
Norway lemmings split off from their sister species, the Siberian lemming, a mere 35,000 years ago. The split occurred just before the peak of the last ice age. This is the finding of genome analyses of several modern lemming species and two individuals from 10,000 to 13,000 years ago (PNAS, 30 June).
Isolated
The Norway lemming (Lemmus lemmus), after branching off, most likely remained isolated. Researchers found no evidence of hybridisation with L. sibiricus, which lives in western Siberia. This is remarkable, because interbreeding in newly formed species is usually common, the two can produce fertile offspring, and the ranges of both lemming species are in close proximity at their edges.
Coat colour
The genome analyses also reveal several mutations that are characteristic of the Norway lemming. These mutations occur, among other places, in genes involved in coat colour and fat metabolism. They presumably contributed to this species’ distinctive black-and-yellow coat, and to its ability to remain active during winter.
The split took place some 34,000 to 68,000 generations ago; this makes Norway lemmings one of the youngest mammal species. Competition for that title comes from, among others, the Chinese goral, which branched off from the Himalayan form 25,000 generations ago.