Fathers have higher motivation for parenting than mothers in common marmoset (Callithrix jacchus)

Abstract

Abstract Parental care is necessary for infant mammals to survive because they are born immaturely. In rodents, the retrieval of pups has been used to evaluate the motivation for maternal behaviour. Common marmosets are cooperative breeders and their parental or alloparental behaviour has been evaluated on the basis of the frequency of carrying infants in a family group. However, under such a situation, the amount of time spent on carrying did not directly reflect the level of motivation for parental or alloparental behaviour because of interference by other family members. To directly evaluate the motivation for such behaviour in common marmosets, animals should be tested where each subject is separated from other family members. Although some groups have applied an infant-retrieval test in which an infant is presented to the subject to evaluate the motivation of each marmoset, there are no studies in which retrieval behaviour is compared among family members. We adopted the infant-retrieval test to compare the motivation for parental or alloparental behaviour among family members: 8 fathers, 8 mothers, 14 older brothers and 9 older sisters. We measured the time from the infant presentation to the retrieval of the infant by each subject as the index of the motivation. We conducted the test when the infant age was 1–8 days old. All the fathers invariably retrieved their infants promptly, but some mothers did not. This variation of responsiveness of mothers was partially explained by the amount of their experience of having their own infants. There was a tendency that inexperienced mothers took a longer time to retrieve infants than experienced ones. Older siblings took a significantly longer time to retrieve infants than fathers during the first few days, but their latency became the same as that of parents in the 8-day test period. Our present findings indicate that the motivation for retrieving infants differs between mothers and fathers. Fathers' motivation is invariably high whereas mothers' is more variable, and that parental and alloparental behaviour may change depending on experience.