EvolSWARM · On the evolutionary significance of wild animal reproductive microbiomes

Our view of microbes has recently undergone a paradigm shift (the so-called microbiome revolution). Previously seen as unwanted harbingers of disease, it is now widely recognised that microbes can be beneficial and that the millions of microbes living in and on the bodies of animals and plants (i.e., the microbiome) can have profound effects on host biology. However, with the exception of the human vaginal microbiome, the microbiome revolution has largely overlooked the reproductive microbiome. This is especially true for wild animals. Yet, if we are to understand the evolutionary significance of host-associated microbiomes it is critical to study them in natural populations, where hosts exhibit greater genetic variability and are exposed to greater levels of environmental and microbial complexity. The aim of this proposal is to determine whether reproductive microbiomes impact host fitness and evolution in wild animals, and reveal the role of host genetics and immune functioning in shaping reproductive microbiome variability. I will leverage a unique wild system the house sparrow that can be studied in natural populations and in the lab, and for which I have recently pioneered the use of microbiome transplant techniques that allows me to disassemble and reconstitute natural microbiomes of nestlings. First, I will determine the fitness consequences and heritability of reproductive microbiomes in a wild population. Second, I will validate the impact of reproductive microbiome variability for reproductive success using novel in vivo microbiome transplants. Third, I will uncover the genetic basis of reproductive microbiome variation. Fourth, I will establish whether host immune functioning shapes reproductive microbiome composition. Altogether, I will significantly advance our understanding of the causes and more importantly the consequences of reproductive microbiomes for host biology and evolution.