Project A4 (PIs Traulsen, Schulenburg) aims to study the role of multilevel selection and microbial transmission mode in shaping host-microbiome interactions, the resulting phenotypes, and the fitness of hosts and associated microbes. The project will combine theoretical models and computer simulations with experimental evolution of the nematode model host C. elegans, for which the selection on the higher level can be controlled and microbial transmission mode can be experimentally manipulated.