EMIGRATION OF MEADOW VOLES, MICROTUS-PENNSYLVANICUS - THE EFFECT OF SEX-RATIO

Exposure to testosterone has been suggested to serve as a trigger for dispersal of female mammals. In male biased litters there is a high probability that a female will be positioned in utero next to one or two males, and hence be exposed to the testosterone produced by the adjacent males. Sex ratio in litters of grey-sided voles, Clethrionomys rufocanus, successfully explain a major portion of the variation in dispersal behaviour of females of this species, thus providing indirect evidence that exposure to testosterone predisposes the females to disperse. Meadow voles, Microtus pennsylvanicus, were raised under laboratory conditions, and the emigration tendency of the young was tested using outdoor enclosures with exit gates. Weight, age, sex ratio and litter size did not explain the variation in emigration of females in this species.