Reproductive control in wild baboons measured by fecal steroids. Biology of Reproduction 55

Measurements of reproductive hormones (progestins and es-trogens) excreted in feces were used to discriminate between 25 conceptive and 76 nonconceptive (including undetected ear-ly abortion) cycles of free-ranging yellow baboons at Mikumi National Park, Tanzania. Conceptive cycles had significantly higher luteal-phase progestin and estrogen concentrations than nonconceptive cycles as early as Day 4 postovulation. However, mean early luteal-phase progestin concentrations in conceptive cycles were lower when conception occurred during ecologi-cally optimal vs. suboptimal times, and among females of high compared to low dominance rank. Mean estrogen concentra-tions in conceptive cycles showed the opposite dominance rank pattern: mean luteal-phase estrogen concentrations were higher in conceptive cycles of high-compared to low-ranking females. None of these relations existed for nonconceptive cycles. These data suggest that successful implantation is facilitated by rela-tively high early luteal-phase progestin and estrogen concentra-tions. However, long-term environmental cues predicting the probability of offspring survival appear to influence the amount of progesterone required for successful implantation; progester-one concentrations necessary to facilitate successful implanta-tion are higher during suboptimal seasons or among females of low dominance rank-cues that also suggest that offspring sur-vival conditions are relatively poor. This may act as a reproduc-tive filter, restricting conception to females whose immediate condition (e.g., low social stress and good physical health) en-ables them to compensate physiologically and behaviorally for effects associated with these relatively harsh offspring survival conditions