What In the Epo-Evo project we aim to better understand how a host animal can control the composition of its gut microbiota through its own genes. This is interesting because it has become increasingly clear that microbes play an important role in driving adaptive evolution of their host. In this project we will study how the epigenome represents an essential, but hitherto ignored, component in understanding how a host animal might control for the presence of beneficial microbes that improve gut health and adaptive potential of the host animal. Why The ability of an animal to manipulate its microbiome has become central to how we understand not only evolution, but increasingly also human, animal and plant health. However, we know little about the actual mechanisms by which associated microbiomes are controlled by their animal host. By documenting the mechanisms by which the epigenome can control gut microbiomes, this project has the potential to introduce a novel angle on how we understand the interactions between an animal and their microbes. Results may have far reaching impacts by also guiding future advances in treatments of diseases caused by microbiome dysbiosis. How We will use zebrafish as a model to explore the importance of the epigenome in controlling the microbiome. We will compare zebrafish with and without modified epigenomes and evaluate differences in their microbiomes caused by the epigenetic changes of specific genes. We will then develop a novel method that uses CRISPR technology as a so-called switch able to turn these genes on or off by inducing epigenetic changes. Lastly, we will demonstrate the same approach in salmon to show how this new method may be used to improve animal health in an important production animal. SSR I expect that our results will provide fundamental new knowledge on epigenome functions including how the epigenome modifies expression of genes that select for the presence of specific gut microorganisms. In the longer term, these results can be used to develop specific tools enabling specific modifications of epigenomes with the aim to improve gut health and wellbeing in animals and humans alike.