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Asymmetry in age suppresses reproduction in female woodland voles, Microtus pinetorum

In many animal societies, only one female in a social group reproduces, while in others all females in a group breed. There are three reasons why younger females may not breed. The lack of reproduction by young females may be due to an inequality in females’ relatedness to each other, to differences in competitive ability between females, or to avoidance of incest with close relatives. We conducted breeding experiments to distinguish among these three possibilities. We found that when there is a bigger difference in age (which is related to differences in competitive ability) between female woodland voles in a family group, the younger female tends not to produce offspring. In contrast, when females were the same age or close in age, both of them tended to produce offspring. We suggest that differences in competitive ability provide the best explanation of the differences in reproduction seen in female woodland voles.

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