A dog's life: Early life histories influence methylation of glucocorticoid (NR3C1) and oxytocin (OXTR) receptor genes, cortisol levels, and attachment styles

Early life deprivation and stress can contribute to life-long, problematic consequences, including epigenetic variations related to behavior and health. Domestic dogs share human environments and social–cognitive traits, making them a promising comparative model to examine developmental plasticity. We examined 47 owner–dog dyads, including dogs rescued from abusive or neglectful environments, and matched control dogs for changes in DNA methylation of glucocorticoid (NR3C1) and oxytocin (OXTR) receptor genes previously shown to be affected by early life stress in other species including humans. We used an attachment paradigm, which included a separation event to examine cortisol levels and owner–dog attachment styles. Overall, dogs with adverse histories had different NR3C1 methylation patterns as a function of age and less OXTR methylation than comparison dogs. Dogs with adverse histories did not differ in their cortisol change from baseline to poststressor from comparison dogs, but the change in cortisol was associated with NR3C1 methylation. In addition, dogs with a history of early life stress had more insecure attachment styles; for every unit increase of OXTR methylation, the odds increased for insecure attachment style. This study demonstrates that adverse life histories lead to methylation differences, resulting in the hypothalamic–pituitary–adrenal (HPA) axis's dysregulation and differences in behavioral phenotypes.