Hormonal responses to parental and nonparental conditions in male cotton-top tamarins, Saguinus oedipus, a New World primate.

The socially monogamous cotton-top tamarin (Saguinus oedipus) monkey is a cooperative breeder with the breeding male providing extensive parental care shortly after birth. We examined the relationship of urinary prolactin and cortisol excretion both to male parental care and as a stress response in the cotton-top tamarin monkey. First-morning urine samples were collected to determine hormonal concentrations. Hormonal and behavioral data were collected on 8 male cotton-top tamarins during the 2 weeks before and the 2 weeks following birth of infants to their mate, 11 nonparental males with exposure to females, and three eldest sons from large family groups. Prolactin levels were significantly higher in experienced fathers during the postpartum period than in the other males, while cortisol levels were significantly lower in experienced fathers and eldest sons. Prolactin levels in experienced fathers were consistently elevated before birth, following birth, and after infants were weaned; prolactin levels during times of infant independence were still significantly higher than those in nonfather males. First-time fathers exhibited prolactin levels that were significantly higher after the births of infants than these same males did when they were paired with nonpregnant females. Elevated prolactin concentrations also occurred prior to the first birth, suggesting that males may be receiving cues from their pregnant females. The elevated prolactin levels in parental males may be associated with the experience of the fathers. Correlation between prolactin levels and number of successful births, number of previous births, and age were high. The care of newborn infants did not appear to be a stressful event since cortisol levels were not elevated postpartum. Both cortisol and prolactin were elevated following capture and injection of saline or a dopaminergic receptor antagonist, indicating that prolactin does respond to acute stress. Cortisol levels did not coincide with prolactin levels except under acute stress conditions, suggesting that different neural pathways are probably involved in prolactin release during parental care versus acute stress. These studies provide evidence that male urinary prolactin levels may be elevated due to cues from pregnant females and the constant exposure of males to the family environment.