Animals, including humans, vary in their phenotypes. While this phenomenon is partially explained by genotype, an organism's environment (and its experiences within a given environment) also contributes to trait variability. Of particular relevance to my dissertation is the notion of developmental plasticity, or variability in an organism's phenotype due to specific environmental exposures experienced across ontogeny. In my dissertation, I discuss theory (Chapter 2) and test empirical hypotheses (Chapters 3-5) regarding the role of developmental plasticity via DNA methylation in the relationship between early life environment and adult phenotype. Leveraging a wild population of spotted hyenas in the Masai Mara, Kenya (The Mara Hyena Project), my analytical Chapters 3-5 specifically focus on social and ecological measures of the early life environment in relation to global (via the luminometric assay [LUMA] of %CCGG methylation) and genome-wide DNA methylation (via Enhanced Reduced Representation Bisulfite Sequencing [ERRBS]). I then explore associations of each with adult stress phenotype, as indicated by fecal corticosterone concentrations. In Chapter 3, I detected differences in %CCGG methylation across the hyena genome with respect to both social and ecological factors early in life, suggesting that these characteristics may impact future phenotype through epigenetic modifications like global DNA methylation. In Chapter 4, I found that higher maternal care and greater social connectedness during early life are associated with higher %CCGG methylation and lower fecal corticosterone concentrations during adulthood, both of which are indicators of positive health. Finally, in Chapter 5, I identified differential methylation in CpG sites involved in inflammatory processes that were associated with both early life maternal care and adult fecal corticosterone levels, thereby implicating these sites as possible mediators to the relationship between early life maternal care quality/quantity and future stress phenotype.These findings are an important extension to current understanding of developmental plasticity that stems from rodent models and studies of captive primates. Biomedical models of developmental plasticity often utilize laboratory rodents, which lack the natural social structure and intact life history involved in development of complex and variable phenotypes. Studies of captive primates typically focus on extreme measures of early life social deprivation that do not capture the naturally occurring spectrum of social experiences in wild mammals. In wild spotted hyenas, I was able to test hypotheses surrounding the concept of developmental plasticity in a gregarious mammal with a complex social structure that is also subject to natural selection. Furthermore, use of data and samples from The Mara Hyena Project enabled me to characterize multiple aspects of the early life environment, DNA methylation, and stress phenotypes in the same individuals - a feat rarely accomplished even in well-established human cohort studies.
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