The reproductive biology and venom system of the parasitoid wasp Nasonia vitripennis : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Genetics at Massey University, Manawatu, New Zealand

Abstract

Nasonia vitripennis (Nasonia) is a parasitoid wasp that uses a wide range of fly species as hosts to support the growth and development of its offspring. This project focused on two important aspects of Nasonia reproductive biology: (1) The role of the endosymbiont Wolbachia pipientis (Wolbachia) in fertility and (2) the functional characteristics of the venom system. The first part of the project focused on a bacterial endosymbiont Wolbachia, which is found in high concentrations within the ovary and sperm cells of Nasonia. As Wolbachia is maternally inherited, it manipulates host reproduction in ways that favour the production of female offspring. In Nasonia, Wolbachia infection results in the generation of reproductive cytoplasmic incompatibilities between infected and uninfected wasps. As very little is known about the molecular mechanism used by Wolbachia to interfere with Nasonia reproduction. RNA-seq was used to identify 84 and 58 genes differentially expressed in the ovary and testis, respectively, in response to Wolbachia infection. RNA interference targeting differentially expressed genes was unable to directly identify functional roles for these genes in cytoplasmic incompatibility, suggesting that this mechanism may be regulated by co-expressed gene networks. Unexpectedly, this study identified a Wolbachia gene (gene1092) that has been incorporated into the Nasonia genome possibly by lateral gene transfer. The second part of the project looked at the Nasonia venom system that has previously been shown to contain a mixture of 79 peptides. The venom is introduced into the host before egg laying and plays a role in altering the host’s physiology in ways that favour development of the parasitoid’s progeny. However, the individual roles venom peptides play in conferring these dramatic changes in the host have yet to be identified. Therefore, RNA interference was used to target venom genes with the goal of better understanding their function roles. Using this approach, it was shown that venom X and venom Z were likely involved in arresting development in the host, while venom Y was likely to be involved in modulating the host’s immune response. As the molecular pathways affected by Nasonia venom underlie important cellular pathways, it is predicted that these venom peptides could be developed into drugs to combat diseases such as cancer, hypertension and diabetes.