Dosage compensation and sexual conflict in female heterogametic methylomes

DNA methylation (DNAm) suppresses gene expression and contributes to dosage compensation in mammals but whether DNAm plays a similar role in female ZW chromosome heterogametic species remains unresolved. We assessed chromosome-level DNAm using whole genome bisulphite sequencing in two avian species, zebra finches and jackdaws. Dosage compensation by DNAm would result in higher and more variable DNAm level in males relative to females on the Z chromosome. However, we found that the level of DNAm and its variance on the Z chromosome was lower in males. Moreover, male Z chromosome based gene promoters were more frequently hypomethylated compared to females, indicating absence of upregulation on a gene-by-gene basis across the female Z chromosome.