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

The partitioning of reproduction in animal societies is a topic of interest to those studying animal behaviour. Under some conditions, two or more females may breed, but lack of reproduction by the younger females occurs frequently. Lack of reproduction by young females may be due to kin asymmetry, dominance asymmetry, or incest avoidance. We conducted breeding experiments to distinguish among these three hypotheses. We show that female reproduction within woodland vole family groups becomes skewed as the asymmetry in age, which is correlated with dominance, between females increases. When daughters were housed with their mothers and a potential mate and the age difference between females was large, we found a high level of skew as compared to females housed with same-age sisters and a potential mate or females housed only with a potential mate. We argue that dominance asymmetry is the best explanation for reproductive skew seen in female woodland voles that have access to unfamiliar, unrelated mates based on reproductive and previous behavioural observations.