AGING AND SOCIAL RANK EFFECTS ON THE REPRODUCTIVE-SYSTEM OF FREE-RANGING YELLOW BABOONS (PAPIO-CYNOCEPHALUS) AT MIKUMI-NATIONAL-PARK, TANZANIA

Ageing and social status effects on reproductive condition are examine d in 106 wild female baboons from 1974 to 1997, The mean duration of e ach reproductive state (follicular and luteal phase components, pregna ncy and lactation) was examined per female, using a repeated measures analysis of variance across each of four age classes (3-6, 7-10, 11-14 , and 15-20+ year olds) and dominance rank quartiles, The sex-skin swe lling portion of the follicular phase increased whereas the fully swol len portion decreased in duration with advancing age and with low domi nance rank. The detumescing portion of the luteal phase increased with advancing age, being most pronounced in lowest ranking females. The n umber of cycles to conception decreased with age, with no dominance ra nk effect. However, owing to variation in lactation duration, the inte rbirth interval was unaffected by age but was shorter in high ranking females. The miscarriage rate was unaffected by age but increased as f emale rank declined. Age and rank effects became significantly more pr onounced in response to a crash in the study population between 1987 a nd 1993, In conclusion, age- and rank-related reproductive changes in baboons, like those in humans, appear to represent attempts to compens ate endocrinologically for accelerated ovarian atresia and increased e nvironmental hardship.