Transcriptomic basis of post-mating responses in females of the parasitic wasp Nasonia vitripennis

Abstract

Mating in insects influences suites of behavioural and physiological changes in females. These changes can include key female traits such as dispersal, foraging, oviposition and female remating or receptivity. Whilst much is known at the phenotypic level about post-mating changes in reproductive biology across many species, much less is known at the genetic level, especially outside of established model organisms such as Drosophila melanogaster. In the parasitic wasp Nasonia vitripennis courtship behaviour, rather than copulation, is believed to be primarily responsible for driving changes in female post-mating behaviour. Here we have studied female receptivity and post-mating gene expression changes associated with courtship and copulation in Nasonia vitripennis. Firstly we considered the influence of the duration of various elements of courtship and mating on female re-mating rates. We were able to identify an association between long pre-copulatory courtship durations and females which are less likely to re-mate (after 24 hours) and suggest that this may be driven by females which are generally less receptive. We also observed that males may be capable of determining female mating state, taking longer to engage in courtship with mated females than virgin females. To further explore the influence of mating on female post-mating behavioural and physiological processes, we explored changes in gene expression occurring in response to mating. To do this we utilised two different transcriptomic sequencing approaches developed for the Illumina next-generation sequencing platform. Using a tag-seq approach we considered the differential gene expression occurring in response to mating in head and body (comprising of the thorax and abdomen) tissues across two time-points (30 minutes and four hours). We were able to identify large changes in expression in head tissues across time-points in comparison to more subtle changes in body tissues. We suggest that head tissues may be more closely associated with post-mating changes in behaviour, whilst body tissues are perhaps physiologically more associated with egg production and influenced less by mating per se. Finally, using an RNA-seq approach, we considered the gene expression changes occurring in female body tissues in response to three elements of male courtship across two time-points (30 minutes and 24 hours). We hoped to narrow down the role of male courtship and/or insemination in post-mating gene expression differences, addressing first the more limited changed in body tissues. We showed that time-point was the most important factor associated with post-mating gene expression, with the courtship components tested being associated with very little expressional change. The data presented in this thesis suggests that male courtship may not be that important for driving the post-mating behavioural and genetic changes seen in Nasonia, perhaps limiting the scope for sexual conflict over reproduction in this species.