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.