DNA methylation reflects tissue and caste identity but not parasitism-induced changes in a social insect

The role of DNA methylation in regulating transcriptional activity and post-transcriptional modifications in insects, particularly in social insects, remains debated. Social insect castes, primarily determined by differential gene expression, exhibit pronounced phenotypic differences in morphology, life history traits and behaviour. In some ants, parasites induce divergent phenotypes, but the role of DNA methylation in this remains poorly understood. In this study, we examined DNA methylation patterns across different tissues (brain and fat body) and castes (queens and workers) in the ant Temnothorax nylanderi. We also compared healthy workers with those infected with the cestode Anomotaenia brevis, which is associated with changes in lifespan, morphology and behaviour. Our results reveal significant differences in gene body methylation across tissues, which were positively linked to gene expression. We also observed caste-specific differences in DNA methylation, particularly in the fat body. Surprisingly, however, we detected no differences in DNA methylation between cestode-infected and healthy workers, despite pronounced differences in transcriptional activity, suggesting that other epigenetic mechanisms exert stronger regulatory control over parasite-induced transcriptional changes. The pronounced differences in DNA methylation between tissues and castes, partly associated with transcriptional variation, warrant further investigation into their functional role, including the modulation of alternative splicing.