Epigenetic changes in red blood cells during the life of chickens exposed to social isolation stress or an enriched environment

From an ecological perspective, many animals, particularly birdstext, are exposed to increasing stress levels in the context of the current climate crisis. Therefore, the development of tools that can reliably measure long-term stress exposure in animals is fundamental. Epigenetic mechanisms offer a promising approach, as stress during early development can alter DNA methylation in peripheral cells, such as avian red blood cells (RBCs). Here, we investigated whether distinct early-life environments leave specific epigenetic marks in RBCs, as well as the persistence of these marks. Male chickens were exposed from day 4 to 3.5 weeks of age to either social isolation stress (SIS), environmental enrichment or control barren conditions. RBCs were collected immediately after exposure and after six months. We found that, with age, SIS increased the number of hypermethylated regions, while enrichment induced mostly hypomethylated regions and fewer overall methylation changes. The control group showed a balanced mix of hyper- and hypomethylated regions. Pathway analysis revealed that differentially methylated region (DMR)-associated genes in SIS were enriched for immune-metabolic pathways, while those in the enrichment group were linked to microRNA regulation and nuclear receptor signalling. Therefore, we show that differing early-life environmental conditions leave persistent and distinct epigenetic signatures in RBCs, with potentially different functional consequences. This article is part of the theme issue 'Ecological epigenetics at the intersection of behaviour and life history variation in non-model animals'.