Carers in cooperatively breeding vertebrates increase food acquisition for offspring; however, they also impact the developmental social environment. One means of linking early-life environments, such as nutrition and social structure, with later-life phenotypes is DNA methylation. Here, using whole-genome methylation sequencing, we measured how additional carers influence DNA methylation in nestlings of the cooperatively breeding chestnut-crowned babbler (Pomatostomus ruficeps). A comparison of nestlings raised by their parents (two carers) and those raised by parents plus additional helpers ('three plus' carers; mean = 4.3 ± 1.4 s.d.) revealed that additional care is associated with genome-wide differences in DNA methylation. Overall, 570 cytosine-phosphate-guanine sites from the regulatory regions of 487 genes were differentially methylated, with 85% being more methylated in nestlings reared by groups. Specifially, sites associated with genes that are integral for metabolism, growth, the regulation and promotion of sociality, the ability to cope with stressors, and cell communication were differentially methylated between the groups. Furthermore, gene ontology-term analysis revealed that differentially methylated sites were over-represented in multiple pathways, including those important for protein binding, metabolism and cell-to-cell and environment-to-cell communication. Our results suggest that the effects of being reared by groups as opposed to pairs in cooperative breeders can extend beyond those typically attributed to nutritional benefits and that these effects are molecularly mediated. This article is part of the theme issue 'Ecological epigenetics at the intersection of behaviour and life history variation in non-model animals'.
Liebl et al. (Thu,) studied this question.