Socio-Ecologic Modulators of Human Females' Reproductive Maturation and Senescence: A Life History Approach

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Females adjust their reproductive strategies according to their environments' physical conditions, such as mortality risks and resource quality and availability. In Homo sapiens, however, social conditions also play a critical role in reproduction. My long-term goal is to develop a synthetic model that integrates all socio-ecological factors affecting human females' reproductive trajectories across their lifespan. Having previously studied female reproductive adaptations during the reproductive phase (first to last birth), my short-term goal is to study two rare reproductive traits for mammalian females: the unusually long, sub-fecund, reproductive transitions bookending their reproductive lifespans: a) menarche to first birth and b) peri-menopause to menopause. These transitions exhibit marked within- and among-population variation in the timing of their onset, duration as well as in fecundability levels. I hypothesize that this variation is the result of complex trade-offs between direct fitness and indirect fitness gains associated with the provision of allomaternal care to close relatives (siblings, nieces and nephews before reproductive maturation; children and grandchildren during menopause). ******Methods: To achieve my goals I will continue a cohort study of 107 Guatemalan Kakchiquel Mayan mothers and 100 of their daughters that I initiated in 2000. To study reproductive maturation and senescence, in 2019/20, I will monitor age related changes in their reproductive status through anthropometric evaluations, menstrual diaries and quantification of reproductive bio-markers. The role of socio-ecological conditions at the community and individual levels will be evaluated through social, demographic, dietary, and resource availability interviews as well as morbidity and mortality risk data. Individuals' energy status and physiologic stress levels will be monitored through dietary diaries and the quantification of urinary biomarkers. I will integrate this information with data I have collected since 2000 from the same individuals. ******Impact: The proposed research will yield the most complete prospective dataset to date to investigate how human females adjust their reproductive strategies according to their cumulative socio-ecological environments in a traditional, subsistence, natural-fertility population. My results will also further our understanding of the role that social networks have on female reproductive development and senescence. The knowledge gained regarding human females' trade-offs between direct and indirect fitness during these two rare reproductive transitions should both, yield novel theoretical insights into the selective processes that have shaped human females' reproductive life histories and guide the study of similar phenomena in other cooperatively-breeding species.