Effects of early-life adversity on the adult phenotype in European starlings

Abstract

During development, individuals are exposed to a variable environment that shapes the adult phenotype. Circumstances that increase exposure to different sources of adversity during early life can significantly affect adult characteristics, extending so far as to contribute to the development of diseases such as depression and anxiety. Such psychological illnesses are the leading causes of disability worldwide, however there is still a significant amount yet to learn about the role that sources of early-life adversity can play in their etiology. Furthermore, even less is known about the mechanisms by which early experience becomes recorded in the adult phenotype. In a cohort of European starling nestlings, we used a unique developmental manipulation designed to dissociate effects of overall quantity of food from the begging investment required to obtain it. When the birds reached adulthood, we set out to investigate how early-life adversity could affect the HPA axis, DNA methylation, depression-like and anxiety-like phenotypes. We showed that different types of adversity can have significant independent effects on different components of HPA profiles, emotional phenotypes and global DNA methylation. We found evidence to suggest that increased exposure to adversity can decrease depression-like behaviour, but increase anxiety-like behaviour. We also showed that changes to the HPA axis are not stable as the birds age. We investigated if changes to the HPA axis were associated with depression-like and anxiety-like behaviour, but found limited evidence to support this hypothesis. Finally, we found that DNA methylation could be shaped by the early environment. We identified significant effects of nutritional restriction on global DNA methylation, with less food as a nestling leading to global DNA hyper-methylation. This work adds support to the hypothesis that different sources of early-life adversity can have significant effects on the adult phenotype.