INDIVIDUAL-DIFFERENCES IN THE MECHANISMS UNDERLYING THE ONSET AND MAINTENANCE OF PATERNAL BEHAVIOR AND THE INHIBITION OF INFANTICIDE IN THEMONOGAMOUS BIPARENTAL CALIFORNIA MOUSE, PEROMYSCUS-CALIFORNICUS

Virgin male Peromyscus californicus tend to behave infanticidally or n onparentally towards pups, whereas virtually all males exhibit parenta l behavior following birth of their own young. Most males (65-75%) liv ing with their pregnant partner attacked or ignored unfamiliar pups an d did not become '' parental '' (behave parentally) prior to birth of their young. However, a significant minority of males (34%) living wit h their partner became parental after just 24 h of postcopulatory coha bitation with the female and remained parental throughout their mate's pregnancy. Males that were infanticidal before the birth of their you ng became parental only after their young were born. The presence of t he mother was necessary for the postpartum maintenance of paternal beh avior and the inhibition of infanticide in males that were infanticida l prepartum. In contrast, males that were paternal prior to birth of t heir young continued to be paternal after birth, even in the absence o f postpartum contact with the mother. Thus, different mechanisms are i nvolved in the inhibition of infanticide and the onset and maintenance of paternal behavior.