Genomic regions exhibiting divergent methylation patterns covary with loci associated with mate choice traits in a stick insect

Speciation involves the development of reproductive isolation between diverging populations. A potential key driver of reproductive isolation is mate choice, a behavioural mechanism that can limit gene flow based on divergence in signal traits. While the genetic basis of mating signal traits has been extensively studied, the contribution of epigenetic modifications to their variation remains underexplored, leaving the role of DNA methylation in mate choice unclear. Here, we focus on epigenetic variation and cuticular hydrocarbons (CHCs), the latter being chemical traits used for mate choice in insects. Specifically, we investigate the association between DNA methylation and regions associated with CHC variation in Timema cristinae stick insects. We integrate analyses of differentially methylated regions (DMRs) between individuals from different host-plant ecotypes with genomic sequencing and phenotypic data on CHCs. We find that DMRs are significantly enriched in genetic loci associated with CHCs, suggesting a non-random relationship between DNA methylation and loci associated with these signal traits. While further work is required to clarify causality, our results highlight the potential for epigenetic marks to be associated with traits involved in mate choice. Future studies should thus aim to establish causal links between DNA methylation and signal trait variation, which would clarify the contribution of methylation to mate choice, prezygotic isolation, and ultimately, speciation.