Costs of Reproduction Among Rhesus Macaque Females on Cayo Santiago

Reproduction is energetically costly for mammalian females during the periods of gestation and lactation and, consequently, is likely to be associated with reduced survival (Stearns 1989, 1992 ; Roff 2002 ) , particularly when maternal condition is poor. Higher mortality may be associated with birth-related complications, but it also may be the consequence of elevated circulating levels of cortisol suppressing immune function (see McEwen et al. 1997 , for a review). If the hypothalamic–pituitary–adrenal (HPA) axis is hyperactivated in post-partum females during prolonged periods as a result of either the energetic demands of lactation or the associated psychosocial stressors, immune function may become impaired, potentially making females more vulnerable to diseases and to increased risk of mortality. Survival costs of reproduction have been documented for a few mammalian species. Among seasonally breeding Columbian and Richardson’s ground squirrels ( Spermophilus columbianus and Spermophilus richardsonii ), adult female mortality is highest in the birth season and during the period of lactation (Michener and Locklear 1990 ; Michener 1998 ; Neuhaus and Pelletier 2001 ) . Among baboons ( Papio spp . ), mortality rates are highest among lactating and pregnant females (e.g., Cheney et al. 2004 ) . The terminal investment and senescence hypotheses both predict that the costs of reproduction should increase with age. According to the senescence hypothesis,