Contrasting epigenetics of Ixodes scapularis populations

Hard ticks are a source of public health concern, in part due to their ability to inhabit different environments. In the United States (US), blacklegged ticks (Ixodes scapularis Say), the primary vector of Lyme disease, exhibit various phenotypes depending on their geographic origin (i.e. northern and southern US ticks). Although genetics may partially explain how blacklegged tick populations acclimate to different environmental conditions across the US, epigenetics may also contribute to their success. Epigenetic mechanisms, such as DNA methylation, might modulate gene expression allowing for rapid adaptation. To gain insight into the potential contribution of DNA methylation, an Enzyme-Linked Immunosorbent Assay (ELISA) was utilized to evaluate differences in DNA methylation levels between blacklegged ticks collected from Minnesota (northern region) and Texas (southern region). DNA methylation profiles from both populations were characterized using bisulfite and nanopore sequencing. Our results revealed significant variability in global methylation levels between southern and northern tick populations, as well as highly variable relative expression of genes encoding DNA methyltransferases and demethylases. Overall, northern blacklegged ticks exhibit lower global DNA methylation levels than southern ticks. Basic proline-rich protein, zinc finger protein 501-like protein, and an uncharacterized protein LOC115333191 are among the genes that exhibit lower DNA methylation. Our findings revealed that blacklegged tick populations possess distinctive DNA methylation profiles, which may contribute to their phenotypic plasticity across the US. This study aims to pave the way for future research into the potential molecular mechanisms that allow ticks to successfully acclimatize to environmental changes.