Epigenetic Properties of Reproduction and Ageing in Hymenoptera

Epigenetic mechanisms expand the genome’s regulatory flexibility. Whilst these mechanisms are conserved across eukaryotes, insects display high variation in DNA methylation profiles making them an ideal study to infer divergent function and evolution of these mechanisms. This thesis explores the role of DNA methylation and histone modifications in two species of Hymenoptera; the eusocial bumblebee Bombus terrestris and the solitary wasp Nasonia vitripennis. Previous work has demonstrated an association between epigenetic mechanisms and the reproductive plasticity found within social insects. I find, in contrast with previous studies, that chemical alteration to the methylome in B. terrestris workers does not induce reproductive morphology and that discrepancies between studies on the role of DNA methylation is due to greater inter-colony variation in DNA methylation than between castes. I also conduct the first investigation into histone modifications between reproductive castes in B. terrestris and find, like DNA methylation, they vary greatly between colonies. I show through both B. terrestris and N. vitripennis that perturbations to the epigenome via chemical modifiers can be inconsistent and highlight the need to more targeted disruption to untangle the function of these epigenetic markers. Given the confounding effect of the genetic background of colonies, I highlight the use of solitary species such as N. vitripennis to determine the functional role of these mechanisms in insects. Finally, due to the association between DNA methylation and ageing in mammals, I investigate DNA methylation and transcriptomic responses in N. vitripennis with ageing. I find hallmarks of ageing in both the methylome and transcriptome as well as a large sex-bias. Overall, this thesis enhances our understanding of epigenetics in Hymenoptera and sheds light on the need for functional validation of epigenetic modifications to further elucidate their role in regulating gene expression and how this impacts plastic phenotypes such as reproduction and ageing.