Costs of reproduction among rhesus macaque females on Cayo Santiago

High allostatic load, characterized by hyperactivation of the hypothalamic-pituitary-adrenal (HPA) axis and the immune system, can make adult mammalian females more susceptible to disease and mortality, particularly during periods of gestation and lactation. Additionally, poor maternal condition or increased maternal investment may affect allostatic load. Long-term demographic records and short-term records on health and behavior were analyzed to examine allostatic load and the costs of reproduction in free-ranging rhesus macaques (Macaca mulatta) on Cayo Santiago. Chapter 2 demonstrates that breeding is seasonal and may be affected by climatic factors and examines how female and male mortality rates in this population are affected by time of year. In Chapter 3, the impacts of female age, reproductive state, social rank and body composition on plasma cortisol levels are explored. In Chapter 4, short-term and long-term records collected on the Cayo Santiago population are used to characterize female senescence in this population and to test whether female age affects intensity of investment in infants and offspring fitness and survival. Chapter 5 explores whether HPA axis activity and immune function are affected by female age, reproductive state, social rank and body condition, whether inter-individual differences in glucocorticoid and cytokine levels are stable over time, and whether there are relationships between glucocorticoid and cytokine levels. Reproductive state and social rank are found to influence cortisol levels in response to stress, and for females there are significant mortality costs associated with the birth season. The data also reflect that females are not all equally equipped to handle the demands of frequent reproduction since allostatic load is chronically elevated for some individuals, as indicated by levels of glucocorticoids or cytokines that remain high from year to year and across pregnancy and lactation. Furthermore, the data support the senescence and terminal investment hypotheses, but though age-associated increases in maternal investment were observed, increased maternal investment did not improve infant survival for mothers in their late teens and early twenties. Although wild rhesus macaques tend to have shorter lifespans than those observed on Cayo Santiago, it is likely that the costs associated with reproduction that have been detected in the Cayo Santiago population would also be observed, perhaps to an even greater extent, in wild primate populations. Disease as well as psychosocial stressors associated with fear of predation and limited resources are likely to increase allostatic load regardless of reproductive state, but are expected to be particularly burdensome among reproductively active females.