Mating May Enhance Rapid Formation of Stable Pair Bonds in the Monogamous California Mouse

Pair bonds are a hallmark of many monogamous species, yet in the monogamous California mouse (Peromyscus californicus) pair-bond formation is poorly understood. While pair bonds are often assumed to be present after a week of cohabitation, when they actually form in this species is debated. To characterize pair bond latency in California mice, we conducted three-chamber partner preference tests for both males and females following 1, 3, 5, or 7 days of cohabitation. Since copulation may contribute to pair-bond formation, animals were paired when females were in estrus and were assessed continuously throughout the cohabitation period for copulatory behavior. We found evidence of pair bonds after 24 h of cohabitation for both sexes with no significant changes in partner preference behaviors across cohabitation periods. Focal animals spent more time in the partner's chamber, were more affiliative toward the partner than the stranger and displayed more aggressive behavior toward the stranger. Affiliative behaviors were consistent between the sexes, while males attacked the stranger more frequently and for longer durations than females. Pairs that copulated prior to partner-preference testing spent more time in the partner's chamber and more time huddling, licking, and grooming their mate than those that did not copulate. We conclude that although copulation may not be necessary for pair-bond formation, sexual receptivity at time of pairing is important for the development of these social relationships and that copulation may serve to enhance pair bonds in California mice.