AGING, INFECUNDITY AND REPRODUCTIVE SENESCENCE IN FREE-RANGING FEMALERHESUS-MONKEYS

The reproductive performance of 760 free-ranging female rhesus monkeys (Macaca mulatta), 168 of whom were 20 years of age and older at the t ime observations were begun, was assessed. The monkeys were resident o n Raccoon Key or Key Lois, two islands located in the Florida Keys, US A. During 1992 and 1993, live birth rates generally declined with age among the Raccoon and Lois females aged eight years and older. This ag e-related deterioration of female fertility was the result of proporti onately more younger females bearing live young during successive birt h seasons, and proportionately more older females experiencing an inab ility to bear live offspring even after a barren year. It is suggested that (I) older females may be more strongly inhibited by the suckling stimulus than are their younger peers, and (2) the risk of a permanen t loss of fecundity increases with each additional year of life or par turition. The live birth rates of females aged 16-24 years were greate r on Raccoon Key than they were on Key Lois, because the Raccoon femal es within this age range were more successful at bearing live offsprin g during successive birth seasons; the reason for this difference coul d not be determined. Inter-population differences in both the body con dition of the females and the severity of female-female competition fo r access to males were not considered to be plausible explanations. It is possible that the difference in female fertility between the islan ds is the result of the greater age of the adult males on Key Lois, or the phytochemicals eaten by the females on Raccoon Key.