Evolution of the Sex Ratio in the Wood Lemming, Myopus schisticolor
The wood lemming (Myopus sohisticolor Lilljeborg) has probably the most unequal sex ratio of all mammals. (The facts in this paragraph are taken from Kalela and Oksala 1966, and Frank 1966.) In wild populations the frequency of males is normally between 0.20 and 0.30. This unequal sex ratio is also found in animals kept in captivity. Kalela and Oksala report that among 1073 new-born lemmings in a population which started from 6 males and 11 females, the frequency of males was only 0.248. The scarcity of males seems to be due to the existence, both in natural and captive populations, of females which mainly or exclusively produce female offspring.
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