Genomic regions exhibiting divergent DNA methylation patterns co-vary with loci associated with sexual signalling traits in a stick insect

The evolution of signalling traits can affect local adaptation, mate choice and the development of reproductive isolation between diverging populations. While the genetic basis of many sexual signalling traits is well characterized, variation in these traits may also reflect regulatory mechanisms, including epigenetic marks. However, the extent to which epigenetic marks, particularly DNA methylation, are associated with signalling traits remains unclear. Here, we focus on epigenetic variation and cuticular hydrocarbons (CHCs), the latter being chemical traits that can be used for mate choice in insects. Specifically, we investigate the association between DNA methylation and loci associated with CHC variation in Timema cristinae stick insects. We integrate previously published analyses of differentially methylated regions (DMRs) between host-plant ecotypes with genome-wide association results for CHCs. We find that DMRs co-vary with genetic loci associated with pentacosanes, the CHC class most strongly implicated in mate choice and sexual isolation in this system. Our documented association between DNA methylation and signalling traits suggests a possible role for epigenetic marks in mate choice and population divergence. Future studies that establish causal links between DNA methylation and signal trait variation are required to clarify the contribution of methylation to mate choice, prezygotic isolation, and ultimately, speciation.