Complex interactions in a host-symbiont-microbiome triangle: The wasp Asobara japonica, the endosymbiont Wolbachia and the remainder microbiome

Recent research on microbial communities suggests that symbiont-induced phenotypes are not caused by the symbiont alone but in interaction with the remainder host microbiome. Despite this, most current investigations limit themselves to binary host-symbiont interactions ignoring potential microbe-microbe and host-microbe interactions. The inclusion of microbe-microbe and host-microbe interactions into host-symbiont studies is needed, as they will not only help to understand symbiotic interactions better but will also to draw general predictions on the possible future of symbioses in our changing world. In this thesis, I investigate the tripartite interaction between the endosymbiont Wolbachia, its host, the parasitic wasp Asobara japonica, and the remainder microbiome. Wolbachia infection in these wasps causes asexual reproduction, which can occasionally fail, potentially due to microbe-microbe or host-microbe interactions. By investigating the complex interactions between host genotype, bacterial community composition and symbiont status in the field and experimentally, I show that the symbiont-induced reproductive phenotype is executed in close interaction with the host genotype and the remainder microbiome. This study, therefore, provides an important first step to deepening our understanding of this tripartite interaction.