Despite a plethora of research on the positive and negative impacts of gut microbiota (community of micro-organisms) and macrobiota (parasitic helminths), as yet there is little focus on how these two sympatric and ubiquitous communities interact. Given that there are increasing evolutionary pressures imposed on microbiota and macrobiota, which have currently unknown system-wide implications, e.g., antibiotic and anthelmintic treatment, it is timely to investigate microbiota-macrobiota interactions. This thesis uses an ecological approach to understand microbiota-macrobiota interactions in a wild rodent system. First, a review of animal gut microbiota literature established the current research landscape of this topic, which highlighted the lack of studies on wild animals, despite the advantages that these animals can provide, e.g., as model systems (Chapter 2). In addition, perturbation field experiments were used to tease apart microbiota-macrobiota interactions in a wild rodent. The impact of helminth removal (using anthelmintic) on microbiota was investigated, which revealed that, with the exception of faecal microbiota composition, gut bacterial communities remained stable following anthelmintic treatment (Chapter 3). Following perturbation of the microbiota (using antibiotic), both fecundity and size of helminths increased (Chapter 4). Helminths were found to be associated with a microbiota that exhibits interspecific variation as well as intraspecific variation, which was driven by gut location of helminths, although composition of helminth microbiota also significantly differed to that of the gut (Chapter 5). Finally, the effect of faecal microbiota on helminth development was tested; egg hatching was less successful in host faeces, compared to faeces from another individual, indicating that faecal microbiota may have some resistance to helminth development (Chapter 6). This thesis highlights the importance of considering systemwide implications of a treatment or perturbation, particularly on gut microbiota-macrobiota interaction
