Temperature predictability and introduction history affect the expression of genes regulating DNA methylation in a globally distributed songbird

Phenotypic plasticity is a major mechanism whereby organisms adjust their traits within-generations to changes in environmental conditions. In the context of range expansions, plasticity is thought to be especially important, as plastic changes in traits can lead to rapid adaptation. One epigenetic process in particular, DNA methylation, enables organisms to adjust gene expression contingent on the environment, which suggests it may play a role in range expansions. At present, we know little about how methylation is regulated in wildlife, especially expression of the enzymes responsible for altering methyl marks on the genome. In this study, we compared expression of three epigenetic regulator genes (DNA methyltransferase 1, DNMT1; DNA methyltransferase 3, DNMT3; and one ten-eleven translocation methylcytosine dioxygenase, TET2) in three tissues (gut, liver, and spleen) of house sparrows Passer domesticus from nine countries. Some countries are in the native range of the species (Israel, the Netherlands, Norway, Spain, and Vietnam) whereas others are sites the species has colonized in the last 150 years (i.e. Australia, Canada, New Zealand, and Senegal). In this exploratory study, we asked whether non-native birds and/or birds from sites with comparatively unpredictable climates would express different levels of these genes. We found that all three genes were expressed more in sparrows from the native range and from areas with more stable temperatures. Expression of all three genes was also strongly correlated among-locations and within-individuals, but mean expression was quite different among tissues. Many factors (e.g. urbanization of the capture site, sex of the bird) did not significantly affect gene expression, but others surprisingly did (e.g. latitude). Our results suggest that these enzymes could be important in range expansions or geographic distribution generally, but more detailed investigations will be insightful.