Prolactin levels are elevated after infant carrying in parentally inexperienced common marmosets.

Alloparental behavior (parental behavior directed to nondescendant young) is pervasive among human cultures but rare among other mammals. New World primates of the family Callitrichidae, including common marmosets (Callithrix jacchus jacchus), dwell in large families and many family members carry and/or provision infants. This study experimentally characterized alloparenting in common marmosets by measuring infant retrieval and carrying outside of the context of the family group. Prolactin was measured in samples collected before and after infant exposure to determine whether elevated prolactin levels were predictive of alloparental responsiveness. Seventeen nonbreeding, parentally inexperienced, singly or peer-housed common marmosets (10 females, 7 males, 6-66 months of age) were tested repeatedly in an infant retrieval paradigm. Infant retrieval was shown by 5 out of 17 monkeys (29%) in their first test. The rate of retrieval increased to 10 monkeys (59%) by the fourth test. No significant differences in age, sex, or housing condition existed between monkeys that retrieved infants and those not retrieving. Prolactin concentrations were significantly elevated in serum obtained after testing only in monkeys that retrieved infants. Prolactin levels after infant exposure were positively related to carrying duration. A separate experiment verified that neither prolactin nor cortisol was significantly elevated in response to prolonged handling. Cortisol levels were inversely proportional to handling time. Prolactin levels were not significantly related to handling time. Our results indicate that alloparental behavior is expressed at high rates after minimal infant experience, and prolactin levels rise concomitantly with the expression of alloparental behavior in this species.

Bromocriptine administration lowers serum prolactin and disrupts parental responsiveness in common marmosets (Callithrix j. jacchus).

The influence of prolactin on parental responsiveness was investigated in eight unpaired, parentally inexperienced common marmosets (Callithrix jacchus; 6 female, 2 male). The marmosets were prescreened with infants (1-10 days of age) and required to exhibit short latency retrieval and infant carrying in at least three consecutive pretests as criterion for inclusion in this study. The marmosets were then administered the dopamine agonist bromocriptine (0.5 mg/0.5ml vehicle subcutaneously) and the vehicle alone (0.5 ml 10% ethanol solution) twice daily for 3 consecutive days in random order. Bromocriptine treatment reduced circulating prolactin to nondetectable levels. Bromocriptine treatment eliminated infant retrieval in four of the eight marmosets and was associated with significantly increased retrieval latencies and significantly reduced carrying durations in the four monkeys that continued to retrieve following bromocriptine treatment. When given the vehicle alone, the marmosets retrieved infants significantly faster than during pretests, suggesting a handling effect of the injection series. Bromocriptine treatments were associated with significantly increased movement during the tests. The results of this study indicate that prolactin and/or its regulatory neurotransmitters are involved in the control of the spontaneous display of parental responsiveness in common marmosets.