Revealing the species- and age-specific effects of social conditions on reproduction can provide insight into the dynamics and evolution of animal social systems. Lagurus lagurus is an arvicoline rodent inhabiting the steppes of Eurasia. Living in extensive habitats and establishing monogamous groups, reported for this species, have been predicted to favour the mechanisms of social control of reproduction. On the other hand, any delay in breeding should be extremely costly for spring-born females in a short-lived multivoltine species. We performed two laboratory experiments to estimate incest avoidance and reproductive suppression by a same-sex competitor, in relation to the age of a focal female of L. lagurus. We also tested if the female reproductive rate in communal groups was affected by dominance asymmetry. In our first experiment, lemmings, independently of female age, displayed strong inbreeding avoidance. In the second experiment, female mortality tended to be higher in polygynous groups than in pairs, but there was no monopolization of reproduction in either sister or matrilineal trios. Latency to the birth of a litter was longer in polygynous than in monogamous primiparous females, but dominance asymmetry did not influence this characteristic. No age-related differences were revealed in the readiness to breed as a member of a communal group. Polygyny reduced the per-female reproductive success of older (about 3 months of age) primiparous females, whereas there was no such effect for younger (about 1 month of age) females.