Pyrenula aspistea isolate:KRB14 Genome sequencing and assembly. Pyrenula aspistea isolate:KRB14

Coevolution can substantially shape the evolution of organisms involved in intimate ecological connections that range from antagonistic to mutualistic relationships. The Red Queen dynamic, which expects faster evolution for interacting organisms, was often brought into play for antagonistic relationships (e.g., host-parasite interactions). However, the coevolutionary effects of mutualistic interactions, which predicted slower evolution for interacting organism (Red King dynamic), were investigated to a lesser extent and lacked empirical evidence. Lichens are a stable, mutualistic relationship of fungi and cyanobacteria and/or algae, which originated several times independently during the evolution of Fungi. Therefore, lichens represent a suitable, replicable system to investigate the coevolutionary effect of mutualism on the fungal genome. We measured substitution rates and selective pressure of about 2000 protein-coding genes (plus the rDNA region) in closely related lineages of lichenized and non-lichenized fungi. Our results show that independent lichenized clades are characterized by significantly slower substitution rates for both synonymous and non-synonymous sites, as predicted by the Red King dynamic for mutualistic relationships. None of these genes indicated that selective pressure is acting on lichenized fungi. Therefore, we hypothesize that this evolutionary pattern is rather connected to the lichen life cycle (longer generation time of lichenized fungi) than a result of different selection strength on lichen genes. This first empirical evidence provides an important insight on how biotic cooperative interactions are able to shape the evolution of symbiotic organisms.