The Role of DNA Methylation in Arthropods.

Epigenetic mechanisms, such as DNA methylation, are poorly understood in arthropods compared to mammals and plants. Arthropods have been shown to display a varietyof DNA methylation profiles across species, making them ideal for understanding the function of DNA methylation outside of a mammalian context. This thesis explores therole of DNA methylation in two arthropod species; the eusocial bumblebee, Bombus terrestris and the freshwater crustacean Daphnia magna.Previous research has implicated DNA methylation in caste determination in some social insect species. I have found differentially methylated genes between worker castesof B. terrestris, some of which are involved in reproduction. However, there was no direct link with differentially expressed genes. This indicates DNA methylation doesnot causally affect gene expression differences between castes.Another possible function of DNA methylation in B. terrestris is the regulation of imprinted genes. Imprinted genes are those which display parent-of-origin allele-specificexpression. Predictions based on the kinship theory state imprinted genes should exist in B. terrestris. I have identified parent-of-origin expression in this species, indicatingsome support for the kinship theory. However, DNA methylation does not appear to be directly mediating this process.The final chapter of this thesis identified DNA methylation changes through time in a single resurrected population of D. magna. A small number of genes which exhibitedDNA methylation changes over time were involved in the production of males, which is usually triggered by environmental change. The data generated in this chapter will be used for novel analyses investigating the adaptive potential of DNA methylation.This thesis has contributed new knowledge to three fields: caste determination in social insects, imprinted genes in social insects and adaptive epigenetics. Taken as a whole, the studies presented here highlight the need for functional validation and the consideration of genotype in future ecological epigenetic research.