Deciphering the molecular mechanisms underlying the photoperiodic clock in the parasitic wasp, Nasonia vitripennis

Nasonia vitripennis is an emerging insect model, with great potential in the field of biological rhythms and seasonality. Nasonia possess a robust a response to photoperiod, in which adult females exposed to short winter-like days generate progeny that will undergo a developmental arrest (diapause). The molecular basis underlying the photoperiodic clock is unknown. We expect this response to be underpinned by changes in gene expression between long (LP) and short (SP) photoperiod exposed wasps. To identify candidate genes, I employed RNA sequencing (RNAseq) to profile the transcriptome of the wasp head in both conditions. This identified 66 transcripts as being significantly differentially expressed (FDR < 0.05). Utilising RNAi, select candidate genes were knocked down in the wasp by injecting dsRNA into pupae. The ability of the wasps to respond to photoperiod (compared to a control group injected with dsRNA against GFP) was assessed. Wasps injected with jhamt dsRNA responded more rapidly to SP conditions with an elevated level of diapause in both photoperiods, while both obp03b and ggt-injected wasps showed no change in response in LP but displayed significantly reduced levels of diapause in SP. These results suggest a causal role for these genes in the photoperiodic response. In a related set of experiments, I have expanded the current knowledge of miRNA composition in the wasp and assessed for the potential role of miRNA in photoperiodism. Through small RNA sequencing, I profiled the changes in miRNA expression in the adult wasp head in response to photoperiod, experimentally validated currently predicted miRNA and predicted a further 106 potential miRNA previously unknown in the wasp. I also explored the potential of maternally deposited miRNA as a mechanism of the transfer of photoperiodic information, as differentially expressed miRNA were observed in young Nasonia embryos, prior to the start of transcription from the zygotic genome. This thesis promotes the use of a new model organism and presents an account of transcriptional and post-transcriptional regulation of gene expression related to seasonal timing in Nasonia vitripennis.