| Individuals exhibit adaptive phenotypic plasticity, in which their behavioral, physiological and cognitive responses are shaped by their environment within the bounds of what is permitted given their genetic makeup. This plasticity is hypothesized to tune an individual to their environment, enabling them to be as successful as possible within the constraints of their current, and predicted future, local context. However, the mechanisms regulating this attunement and the specific consequences, especially in the cognitive realm, have not yet been investigated in a systematic, longitudinal and natural manner. In this dissertation, I examine the effects of variation in early life environment, as assessed via mother-infant interactions and maternal regulation of the infant social environment, on the development of cognition, behavior and physiology in free-ranging infant rhesus macaques living on Cayo Santiago, Puerto Rico. Chapter 2 demonstrates that infant social cognition is shaped by the early life environment, potentially via maternal regulation of infant exposure to social risk, and that attentional bias to social threat appears within the first year of life but is not present at birth. Chapter 3 examines infant responses to extreme stress, and finds that behavioral and cognitive stress-reactivity does not correspond to reactivity of the Hypothalamic-Pituitary-Adrenal (HPA) axis. However, Chapter 4 shows activation of the HPA axis in response to a more natural stressor, weaning conflict and maternal rejection from nursing, demonstrating that mothers can induce a stress response in their infants which might serve to tune their infant's long-term HPA axis activity to local resource availability. Chapter 5 investigates one possible source of variation in mother-offspring interactions, testing the hypothesis that maternal body condition can predict the timing and intensity of parent-offspring conflict, thus providing a proximate explanation for inter-individual variation in maternal behavior. Together, these studies investigate the concept of adaptive phenotypic plasticity and provide a comprehensive look at the where variation in early life experience comes from and the behavioral, physiological, and cognitive consequences of this variation. The relationships between these phenotypic components and the selection, development, and adoption of a life-history strategy are discussed with an eye to future studies. |
