PS 19-187 - Early life adversities and stage-specific vulnerability in a non-human primate

Background/Question/Methods

Ecological and psychosocial adversities affect the demographic performance of individuals within populations. However, the impact adverse conditions can have on future survival as well as the developmental and early life exposures generating individual differences in risks of death remain unknown. To quantify the effects of early life adversity and identify the early life stage most vulnerable to such conditions, we analyzed 8,130 individual life histories of Cayo Santiago rhesus macaques over the span of 48 years. We identified four sources of early life ecological and psychosocial adversities during infancy and juvenility: population density, major hurricanes, maternal loss, and the presence of a competing younger sibling, and tested whether these individual factors at each stage compromised later life survival using time-varying Cox proportional hazards models. Following this, we tested the effects of aggregated adversities at each stage on later life survival using a cumulative adversity index and a Cox proportional hazards model.

Results/Conclusions

Our analysis shows that sex, density at birth and maternal loss during infancy are associated to survival past infancy (cumulative model weight = 0.92). Females had a 15.98% reduction in risk at each age (HR=0.84; 95% CI: 0.77, 0.92), relative to males. Density at birth ranged from 73 to 494 and our model indicated that increasing density at birth by one individual increased risk at each age by 0.08% (HR=1.00, 95% CI:1.0003,1.0012). Individuals who lost their mothers during infancy had a 70.12% risk increase at each age before reaching five years of age (HR=1.70; 95% CI: 1.24, 2.33), relative to individuals who did not experience this adversity early in life. Once reaching five years of age, such annual risk decreased to 0.51% (HR=1.01, 95% CI: 0.70, 1.44). After controlling for sex-specific differences, an accumulation of one of these significant adversities during infancy increased risk by 71.70% at each age until age two but became non-significant afterwards (cumulative model weight = 1.0; HR=1.72; 95% CI:1.46, 2.02). Our findings support early life adversity and cumulative adversity frameworks and suggests that infancy, not juvenile ages, is the most vulnerable early life stage to harsh conditions in rhesus macaques.