Inseminated Female Mice (Mus musculus) Investigate Rather Than Avoid Novel Males That Disrupt Pregnancy, but Sires Protect Pregnancy

Experiment 1 replicated the Bruce effect, showing pregnancy termination in CF1 strain female mice (Mus musculus) housed underneath novel heterogeneous strain (HS) males. In a 4-arm maze in Experiment 2, inseminated CF1 females approached novel HS males more often than CF1 sires or unfamiliar CF1 males. In Experiment 3, inseminated females showed random nesting sites when housed continuously underneath 4 compartments containing the sire, a novel CF1 male, a novel HS male, and no stimulus. In Experiment 4, when inseminated females were housed with or without the sire below novel HS males, the sire's presence decreased female interaction with novel males and mitigated the Bruce effect. Inseminated females do not reliably avoid males that disturb pregnancy unless the sire is immediately present.