In this project we set out to study the genetic mechanisms of convergent evolution, by uncovering the mechanistic details of two highly replicated transitions in cellularity level. Convergent evolution is widespread in nature, even at macroevolutionary time scales. To explain its pervasive occurrence, recent studies have put forth the idea of predisposing precursor traits that, if easily co- or exapted for new functions, can increase the likelihood of convergence. However, most such hypotheses remain untested due to the lack of model systems that are tractable in the laboratory. We here identified two fungal case studies that offer optimal model systems to mechanistically test the hypothesis that predisposing traits increase the likelihood of convergence: (i) the 8-11 repeated origins of complex multicellularity in mushrooms and (ii) >14 losses of multicellularity in yeast-like fungi. We hypothesize that both of these happened by the repeated exaptation of ancient morphogenetic programs and, in the case of yeasts, additionally, of mechanisms for bypassing multicellular growth. Our hypotheses imply that both complex multicellular and yeast-like lifestyles are only a few mutations away for any filamentous fungus, because precursor traits shorten the mutational path for evolution. We designed an experimental plan involving phylogeny-aware comparative -omics, reverse genetics and evo-devo, which, combined with our preliminary results, will provide a robust entry point into testing the role of predisposition in convergent evolution and will ultimately allow us to ‘replay the tape of major fungal transitions’ in the laboratory. We expect this project to contribute to uncovering the general principles of convergent evolution and to be one of the first to mechanistically prove that certain precursor traits can promote convergence.
