Associations between fecal cortisol and biparental care in a pair-living primate.

OBJECTIVES: We quantified variation in fecal cortisol across reproductive periods in Azara's owl monkeys (Aotus azarae) to examine physiological mechanisms that may facilitate biparental care. Specifically, we evaluated evidence for the explanation that owl monkeys have hormonal mechanisms to mobilize energy during periods when each sex is investing heavily in reproduction, that is, the gestation period for females and the infant care period for males. MATERIALS AND METHODS: Between 2011 and 2015, we monitored 10 groups of Azara's owl monkeys from a wild population in Formosa, Argentina and collected fecal samples from 26 adults (13 males, 13 females). Using enzyme-linked immunosorbent assays, we quantified fecal cortisol as a proxy for evaluating stress responses, including energetic demands, on both sexes during periods of reproduction and parental care. RESULTS: Male cortisol was lowest during periods when they were caring for young infants (<3 months) compared with periods with older infants or no infant. Female cortisol was elevated during gestation compared with other periods. Mean fecal cortisol in both males and females was lower when an infant was present compared with when females were gestating. DISCUSSION: Our results do not support the hypothesis that owl monkey males have elevated fecal cortisol during periods when they need to mobilize energy to provide intensive infant care. Our findings are also inconsistent with the Maternal Relief hypothesis. However, results from studies measuring fecal cortisol must be interpreted with care and alternative explanations, such as seasonal fluctuations in diet and thermoenergic demands, should be considered when drawing conclusions.

Individual variation in paternal responses of virgin male California mice (Peromyscus californicus): behavioral and physiological correlates.

California mice Peromyscus californicus are a rodent species in which fathers provide extensive paternal care; however, behavioral responses of virgin males toward conspecific neonates vary from paternal behavior to tolerance to infanticide. Indirect evidence suggests that paternal responses might be influenced by social status potentially through increased stress and anxiety in subordinate males. To test this hypothesis, we housed 12 virgin male California mice in same-sex dyads on weaning and assessed their within-dyad subordinate or dominant status using food-competition and urine-marking tests. In addition, behavioral responses to an unrelated pup, expression of vasopressin (AVP) and corticotropin-releasing hormone (CRH) mRNA in the paraventricular hypothalamic nucleus (PVN), basal plasma levels of testosterone and corticosterone, and body mass were measured. Food-competition and urine-marking tests did not reveal strong or stable dominance-subordination relationships in male-male dyads. Latency to sniff a newborn pup was correlated negatively with urine marking in the center of a novel environment and positively with expression of AVP mRNA in the PVN. Because these three parameters are all associated with state anxiety in other rodent species, these results suggest that individual differences in paternal responsiveness may be influenced by individual differences in anxiety but not necessarily by social status in virgin male California mice.

Acute effects of corticosterone injection on paternal behavior in California mouse (Peromyscus californicus) fathers.

Glucocorticoids are thought to mediate the disruption of parental behavior in response to acute and chronic stress. Previous research supports their role in chronic stress; however, no study has experimentally tested the effects of acute glucocorticoid elevation on paternal behavior. We tested the prediction that acute corticosterone (CORT) increases would decrease paternal behavior in California mouse fathers and would lead to longer-term effects on reproductive success, as even short-term increases in CORT have been shown to produce lasting effects on the hypothalamic-pituitary-adrenal axis. First-time fathers were injected with 30 mg/kg CORT, 60 mg/kg CORT or vehicle, or left unmanipulated. Interactions between the male and its pup(s) were recorded 1.5-2h after injection and scored for paternal and non-paternal behavior. Treatment groups were combined into control (unmanipulated + vehicle, n = 15) and CORT (30 mg/kg + 60 mg/kg, n = 16) for analysis based on resulting plasma CORT concentrations. CORT treatment did not alter paternal or non-paternal behaviors or any long-term measures (male body mass or temperature, pup growth rate, pup survival, interbirth interval, number or mass of pups born in the second litter). Fathers showed a significant rise in body mass at day 30 postpartum, followed by a decrease in body mass after the birth of the second litter; however, this pattern did not differ between the CORT and control groups. In summary, acute elevation of plasma CORT did not alter direct paternal behavior, body mass, or reproductive outcomes, suggesting that acute CORT elevation alone does not overtly disrupt paternal care in this biparental mammal.

Food transfers to young and mates in wild owl monkeys (Aotus azarai).

Accounts of food sharing within natural populations of mammals have focused on transfers to offspring or transfers of food items that are difficult to obtain (such as meat). Five groups of socially monogamous owl monkeys (Aotus azarai azarai) in Formosa, Argentina were observed during 107 hr to determine the pattern of food sharing under natural conditions. There were a total of 42 social interactions involving food with food being transferred on eight occasions. Adult males transferred food to young more often than did adult females. All types of food that were readily obtained and eaten by all age/sex classes were transferred to young. Adult females also transferred food to their mates. This type of food sharing is very rare among animals and may have social benefits specific to monogamous mammals with paternal care.