Tue, Aug 03, 2021:On Demand
Background/Question/Methods
Adversity early in life can have negative effects on health and lifespan that result in changes to the reproductive potential of many organisms. Less research has been done however on how intense, single-time, adverse conditions early in life can affect organisms later in life. In this study we quantified how both population density and major hurricanes early in life have affected the reproductive metrics of the Cayo Santiago rhesus macaque population. Specifically, we used mixed-effect models to quantify the effects of density and hurricane-induced early-life ecological adversity on (1) mean age-specific fertility, (2) age at reproductive debut and inter-birth intervals (IBI), and (3) lifetime reproductive success (LRS). The Cayo Santiago monkeys comprise an informative system as they allow for a high density of longitudinal observations that include individuals with known life histories affected by ecological adversities.
Results/Conclusions Early-life adversity delays reproductive debut, but such delay is compensated at prime reproductive ages. Females experiencing major hurricanes early in life exhibited a lower mean fertility during early ages (3-5 years) and a higher mean fertility during reproductive prime ages (6-15 years), relative to females not experiencing them. Additionally, high density had a negative effect on fertility across most age classes. Females experiencing a major hurricane early in life showed a delayed sexual maturity debuting at a median age of 4.55 (95% CI: 3.86, 5.89) years in contrast to females from the non-hurricane cohort who debuted at a median age of 4.08 (3.73, 5.79) years. Increased density at birth was also associated with a delayed reproductive debut. We found no hurricane effects on IBI. However, our analysis does suggest age-specific differences and density effects on IBI. Age-specific effects were nonlinear with very young and very old females exhibiting the highest IBIs, while density effects were overall negative. We found no hurricane effects on LRS, though LRS was found to decrease with increasing density at birth. Females from the hurricane cohort had a median LRS of 2 offspring (0, 7). Similarly, females from the non-hurricane cohort had a median LRS of 2 offspring (0, 10). The age-specific fertility and LRS analyses suggest that although the hurricane-exposed monkeys suffer from an early reproductive delay, they overcome this later in life. We hypothesize that the observed delay in reproductive debut and later-life reproductive compensation for it is an evolutionary strategy to maintain fitness in the population once the initial penalty has been experienced.
Results/Conclusions Early-life adversity delays reproductive debut, but such delay is compensated at prime reproductive ages. Females experiencing major hurricanes early in life exhibited a lower mean fertility during early ages (3-5 years) and a higher mean fertility during reproductive prime ages (6-15 years), relative to females not experiencing them. Additionally, high density had a negative effect on fertility across most age classes. Females experiencing a major hurricane early in life showed a delayed sexual maturity debuting at a median age of 4.55 (95% CI: 3.86, 5.89) years in contrast to females from the non-hurricane cohort who debuted at a median age of 4.08 (3.73, 5.79) years. Increased density at birth was also associated with a delayed reproductive debut. We found no hurricane effects on IBI. However, our analysis does suggest age-specific differences and density effects on IBI. Age-specific effects were nonlinear with very young and very old females exhibiting the highest IBIs, while density effects were overall negative. We found no hurricane effects on LRS, though LRS was found to decrease with increasing density at birth. Females from the hurricane cohort had a median LRS of 2 offspring (0, 7). Similarly, females from the non-hurricane cohort had a median LRS of 2 offspring (0, 10). The age-specific fertility and LRS analyses suggest that although the hurricane-exposed monkeys suffer from an early reproductive delay, they overcome this later in life. We hypothesize that the observed delay in reproductive debut and later-life reproductive compensation for it is an evolutionary strategy to maintain fitness in the population once the initial penalty has been experienced.