Failure of strange females to cause pregnancy block in collared lemmings, Dicrostonyx groenlandicus

The effects of exposure to unfamiliar females on pregnancy success of recently mated females were examined in collared lemmings (Dicrostonyx groenlandicus). Four days after mating, females in their home cage were exposed to strange, female intruders that were either nonpregnant or 16 days pregnant. Other recently mated females were introduced to the home cage of 16-day-pregnant females. Pregnancy success of the recently mated females was not reduced in any of these treatments. In the paired encounters, there was no relationship between dominance status and pregnancy status, nor between dominance and pregnancy success. These results do not support the hypothesis that in species in which females are aggressive and readily commit infanticide, unfamiliar females should cause other females to terminate early-stage pregnancies.