S. Peter Henzi

The physiological performance of a mother during reproduction represents a trade‐off between continued investment in her current offspring, and the mother's own survival and ability to invest in future offspring. Here, we used core body temperature ( T b ) patterns to examine the degree to which maternal body temperatures support the infant during periods of gestation and lactation. We implanted 30 wild vervet monkeys ( Chlorocebus pygerythrus ) with miniature data loggers to obtain continuous measurements of core T b during periods of typical (i.e. non‐drought periods) and limited (i.e. drought period) resource availability. We tracked maternal T b profiles across the gestation and lactation periods, associated with 23 births, and compared those with T b profiles of non‐reproductive females. This allowed us to examine the flexibility in maternal body temperatures and test whether limited resource availability shifts priority away from offspring investment and towards self‐maintenance. Vervet monkeys demonstrated the predicted pattern of gestational hypothermia and improved homeothermy in the gestation period during typical conditions, consistent with the maintenance of a thermal gradient to facilitate heat loss from the foetus. During periods of limited resource availability (i.e. drought), mothers were less homeothermic and more hyperthermic during the gestation period. Vervet monkeys showed no evidence of lactational hyperthermia during typical conditions. During the drought, lactating mothers demonstrated hyperthermia and increased variability in body temperature, consistent with the increased metabolic demands and water requirements for milk production required to support growing infants. Although a mother's degree of homeothermy during gestation and lactation was unrelated to her infant's chance of survival to weaning, mothers did show flexibility in the degree to which they prioritized the maintenance of a thermal environment that supports their infant's development. Together, our findings demonstrate that flexibility in a mother's investment in thermoregulation during gestation and lactation may reflect a bet‐hedging trade‐off between self‐maintenance and offspring investment. Read the free Plain Language Summary for this article on the Journal blog.

Objectives We consider the relative contributions of maternal rank and sociability to the survival of infant vervet monkeys ( Chlorocebus pygerythrus ) to nutritional independence (~210 days) in a generally resource‐poor environment. Methods We analyzed survival data from 153 infants born to 60 mothers across three free‐ranging troops and 10 yearly birth cohorts at a South African research site experiencing general but variable resource scarcity. Results The population was characterized by a pre‐weaning mortality of 30% (Range: 9%–85%), with a median age at death of 50 days. In addition to the consequences of resource availability, increased infant survival was independently and equivalently positively associated with higher maternal rank and a greater number of maternal spatial partners. Discussion We use this outcome to suggest that apparent discrepancies across sites and species in the relative importance of different maternal attributes in determining reproductive outcomes may be resolved by considering more closely local sources of infant mortality.