Project C4 (PIs Rainey, Hentschel) aims to explore the role of mobile genetic elements (MGEs) as regulators of host-associated microbial community composition and function. The project will build on the established Metaorganism Evolution Experiment (MEE) approach to provide detailed insights into the dynamics of evolutionary change under conditions that either promote or hinder MGEs in two host-microbe pairs: the worm C. elegans and Ochrobactrum, and the sponge H. panicea and Vibrio.