Comparing Predictors and Outcomes of Higher Allostatic Load across Zoo-Housed African Great Apes

Stressors over the lifespan can contribute to physiological dysregulation, or allostatic load. Allostatic load has been studied in humans using allostatic load indices (ALIs) for over 25 years, but the same methods are rarely applied to other species. We constructed an ALI for zoo-housed western lowland gorillas, chimpanzees, and bonobos and tested potential predictors of and health outcomes associated with allostatic load. Allostatic load scores ranged from 0-6 for gorillas and chimpanzees and 0-7 for bonobos. Age was significantly associated with allostatic load in gorillas and chimpanzees but not bonobos. Cumulative stressful events were positively associated with allostatic load in chimpanzees. Wild-caught gorillas had higher allostatic load than zoo-born conspecifics, but rearing differences between zoo-born animals were not significant for any species. Age may affect associations of allostatic load with stressful events and birthplace as results change when it is included as a covariate. Allostatic load was not retained in best-fit models for risk of all-cause morbidity, cardiac disease, or mortality risk. Some analyses herein were limited by the use of retrospective data, such as reason for sample collection and length of records provided for individual animals. Nevertheless, these data indicate additional research is needed to optimize ALIs for non-human primates.