Sex ratio evolution in lemmings.

In the varying lemming, Dicrostonyx torquatus, numerous XY females occur due to the X-linked mutation X*. Gileva (1987) has shown that there is also segregation distortion in males, with the segregation ratio for Y sperm being about 0.56, which has a significant effect on the sex ratio and the frequency of XY females. A theoretical analysis shows that this degree of segregation distortion is expected to evolve in the Dicrostonyx system under random mating, provided that reproductive compensation for the loss of YY zygotes by XY females is largely an automatic process due to reduced competition between the surviving embryos. The evolution of segregation distortion makes it unlikely that X* is an adaptation to allow a female-biased sex ratio in response to population structure.