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

Virgin male Peromyscus californicus tend to behave infanticidally or nonparentally towards pups, whereas virtually all males exhibit parental behavior following birth of their own young. Most males (65-75%) living with their pregnant partner attacked or ignored unfamiliar pups and did not become '' parental '' (behave parentally) prior to birth of their young. However, a significant minority of males (34%) living with their partner became parental after just 24 h of postcopulatory cohabitation with the female and remained parental throughout their mate's pregnancy. Males that were infanticidal before the birth of their young became parental only after their young were born. The presence of the mother was necessary for the postpartum maintenance of paternal behavior and the inhibition of infanticide in males that were infanticidal prepartum. In contrast, males that were paternal prior to birth of their young continued to be paternal after birth, even in the absence of postpartum contact with the mother. Thus, different mechanisms are involved in the inhibition of infanticide and the onset and maintenance of paternal behavior.