Abstract
Epigenetics focuses on how genetic and phenotypic changes may occur by mechanisms that do not alter the DNA sequence. Methylation of DNA is one of the best understood epigenetic marks especially for its role in the regulation of gene expression. In animals, methylation occurs primarily at cytosines that are followed by guanines, so-called CpG sites. However, this methylation mark is mutagenic and as a consequence are C→ T mutations at CpG sites much more common than other point mutations. Recombinationinduced DNA repair, on the other hand, is biased towards G and C bases and hence increases the GC content in highly recombining regions. Currently, little is understood about the interplay between these two counteracting forces. Birds are well suited to resolve this conundrum because their genomes are characterized by an extremely heterogenic recombinational landscape. Here we use whole genome and methylome information of the passerine bird Parus major in a population genetic framework to disentangle the effects of GC-biased gene conversion and methylation-induced mutation bias. We show drastic imprints of selection on and around DNA methylation sites revealing how this important epigenetic mark has evolved in animal species.
