Socio-ecological and endocrine predictors of cycling irregularity in the wild baboon (Papio cynocephalus): A life history characterization

Abstract

This study explores the environmental and social factors that combine to exert similar effects in the menstrual patterning of a population of wild yellow baboons (Papio cynocephalus) in Amboseli, Kenya. Irregular cycles are associated with significantly reduced fertility as well as fetal loss in both humans (Rowland et al 2002)(Bently 1985)(Gluckman and Hanson 2006) and baboons (Altmann and Alberts 2003)(Gesquiere et al 2006), but the exact forces responsible for such compensatory or senescence-related menstrual irregularity remain uncertain. The indirect effects exerted by psychological and physiological stress on sex hormones via the hypothalamic-pituitarygonadal axis are well documented. However, greater specificity of life history patterns in postpartum amenorrhea and cycling irregularity needs to be established in order to assign comparative weight to underlying socio-ecological forces, and to assess separate long-term consequences of these occurrences (Livingston 2012). The main findings of this study are as follows: When drought was concurrent with a female’s adolescent sub-fertility, she required two more cycles on average to achieve first conception. Drought preceding her maturation yielded no significant difference in the number of cycles required for her first conception. Concurrent drought conditions interacted with multiparous females’ rank and her fGC hormone concentrations to predict longer PPA duration, however drought alone was not a significant predictor of longer PPA. Instead, lower rank was a stronger predictor of lengthier PPA duration; rank demonstrated an even stronger correlation with PPA during drought conditions compared with non-drought and for primiparous females compared with multiparous females. Primiparous females exhibited longer PPA than multiparous females (controlling for the effects of rank, age, fGC, drought, and accounting for female identity). Older age was not a significant predictor of longer PPA duration after fGC was controlled for. Higher fGC hormone concentrations predicted longer PPA, when all of the aforementioned socio-ecological predictors were controlled for. Infantile death rates (defined by survival < 1 year) were significantly higher when drought preceded parturition, while primiparous females also exhibited significantly higher infantile death rates than multiparous females. Longer non-conceptive cycles did not occur more frequently during drought conditions.