Genome‐wide DNA methylation signatures of infection status in Trinidadian guppies ( Poecilia reticulata )

Epigenetic modification, especially DNA methylation, can play an important role in mediating gene regulatory response to environmental stressors and may be a key process affecting phenotypic plasticity and adaptation. Parasites are potent stressors with profound physiological and ecological effects on their hosts, yet it remains unclear how parasites influence host methylation patterns. Here, we used a well‐studied host–parasite system, the guppy Poecilia reticulata and its ectoparasitic monogenean Gyrodactylus turnbulli to gain mechanistic insight into the dynamics of DNA methylation in host–parasite interactions. To explore this, we quantitatively measured genome‐wide DNA methylation in guppy skin tissue using reduced representation bisulphite sequencing and characterized differential methylation patterns in guppies during distinct phases of infection. We identified 365, 313, and 741 differentially methylated regions ( DMR s) between infected and control fish in early infection , peak infection and recovery phases, respectively. The magnitude of the methylation difference was moderate in DMR s, with an average of 29% ( early infection ), 27% ( peak infection ) and 30% ( recovery ) differential methylation per DMR . Approximately 50% of DMR s overlapped with CpG islands, and over half of the DMR s overlapped with gene bodies, several of which encode proteins relevant to immune response. These findings provide the first evidence of an epigenetic signature of infection by ectoparasites and demonstrate the changing relationship between epigenetic variation and immune response in distinct phases of infection.