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Abstract

Throughout their evolutionary history, animals have been continuously exposed to a great diversity of microbial species with which they have co-existed across various types of environments. So far, our knowledge about the co-evolutionary dynamics between hosts and their symbiotic microbial communities remains poor and is nearly exclusively derived from gut-associated microbiota, while further barrier organs including the skin harbor diverse and complex microbial communities. Indeed, only few studies addressed the impact of skinassociated microbiota on host fitness, and even fewer inspected the forces shaping interindividual variability of the skin microbiota. Using the house mouse as a model organism, in my thesis projects, I aimed to bring new insights into the evolutionary and ecological processes that govern the skin-associated bacterial communities. In a first study, by employing several mouse lines that represent various evolutionary distances, I evaluated the effects of environment and host genetics in shaping the composition and diversity of the standing (DNA-based profiling) skin microbiota. I found a large influence of the external environment and a moderate effect of host genetics on the composition and diversity of skin bacterial communities. Second, to further quantify and define host genomic regions that co-vary with abundances of skin bacterial taxa, I performed high-resolution QTL mapping on standing and active (RNA-based profiling) skin microbiota using the fifteenth generation of an advanced intercross mouse population. The defined QTLs span narrow intervals, while some target single host genes. Additionally, the number of QTLs within the active communities is considerably higher compared to the standing communities, suggesting that profiling the skin microbiota at the transcript level provides stronger signals about host-microbiota interactions. Finally, in order to uncover similarities and divergences in community diversity and structure of the skin microbiota between natural and laboratory reared populations of house mice, I thoroughly compared the composition and structure of both standing and active bacterial communities of wild and laboratory individuals. This first of its kind investigation reveals extensive overlap in the community membership of wild and laboratory mice, indicating that communities assembled in a similar manner. Interestingly, we report significant structural changes between these two mouse groups along with a greater inter-individual variation within the laboratory reared mice. Together, these findings meaningfully extend our current knowledge about the forces that govern the diversity of skin-associated bacterial communities.