Pollutants, such as toxic metals, negatively influence organismal health and performance, even leading to population collapses. Studies in model organisms have shown that epigenetic marks, such as DNA methylation, can be modulated by various environmental factors, including pollutants, influencing gene expression, and various organismal traits. Yet experimental data on the effects of pollution on DNA methylation from wild animal populations are largely lacking. We here experimentally investigated for the first time the effects of early-life exposure to environmentally relevant levels of a key pollutant, arsenic (As), on genome-wide DNA methylation in a wild bird population. We experimentally exposed nestlings of great tits ( Parus major ) to arsenic during their postnatal developmental period (3 to 14 days post-hatching) and compared their erythrocyte DNA methylation levels to those of respective controls. In contrast to predictions, we found no overall hypomethylation in the arsenic group. We found evidence for loci to be differentially methylated between the treatment groups, but for five CpG sites only. Three of the sites were located in gene bodies of zinc finger and BTB domain containing 47 ( ZBTB 47), HIVEP zinc finger 3 ( HIVEP 3), and insulin-like growth factor 2 mRNA binding protein 1 ( IGF 2 BP 1). Further studies are needed to evaluate whether epigenetic dysregulation is a commonly observed phenomenon in polluted populations and what are the consequences for organism functioning and for population dynamics.

Pollutants, like toxic metals, negatively influence organismal health and performance, even leading to population collapses. Studies in model organisms have shown that epigenetic marks, such as DNA methylation, can be modulated by various environmental factors, including pollutants, influencing gene expression and various organismal traits. Yet experimental data on the effects of pollution on DNA methylation from wild animal populations is largely lacking. We here investigated experimentally for the first time the effects of early-life exposure to environmentally relevant levels of a key pollutant, arsenic (As) on genome-wide DNA methylation status in a wild bird population. We experimentally exposed nestlings of great tits (Parus major) to arsenic during their post-natal developmental period (3 to 14 days post-hatching) and compared their DNA methylation levels to those of respective controls. In contrast to predictions, we found no overall hypomethylation in the arsenic group. We found evidence for loci to be differentially methylated between the treatment groups, but for five CpG sites only. This may be explained by the heterogenous, environment, relatively low dose (compared to previous laboratory studies), or choice of tissue. Further studies are needed to evaluate whether epigenetic dysregulation is a commonly observed phenomena in polluted populations, and what are its consequences for organism functioning and for populations.