DNA methylation is widespread across social Hymenoptera

Genomic imprinting is an epigenetic phenomenon by which the expression of a gene is influenced by the parent from which it is inherited. The evolutionary causes of imprinting are mysterious but it is likely to represent a form of within-genome conflict [1]. For instance, alleles inherited from the father and the mother will be in conflict over treatment of relatives to which they are differently related. In this context, natural selection may favor alleles with effects that differ depending on the allele's parental origin [1,2]. This 'kinship theory of imprinting' has been developed and tested largely in the context of parental provisioning of offspring [1,2]. Given their haplodiploid genetic system and interspecific variation in social traits, the Hymenoptera (ants, bees, and wasps) provide a large variety of novel contexts in which to examine this theory [2]. However, aside from evidence that imprinting determines sex in the parasitic wasp Nasonia vitripennis [3], and a QTL that appears to be paternally inherited in the honeybee [4], nothing is known about imprinting in this group of animals. Here we provide evidence that CpG methylation, a hallmark of imprinting, is ubiquitously present in social insects but the proportion of methylated sites varies substantially among species and developmental stages.