Major transitions made easy? In search of genetic preconditions that help the repeated evolution and loss of fungal multicellularity

In this project, we aim to study the genetic mechanisms of convergent evolution by uncovering the mechanistic details of two highly replicated transitions in organismal complexity. Convergent evolution is widespread in nature, even on macroevolutionary timescales.

To explain its pervasiveness, recent studies have proposed the idea of predisposing precursor traits that, if easily co- or exapted for new functions, can increase the likelihood of convergence. However, most of these hypotheses remain untested because of the lack of tractable model systems.

We identified two fungal case studies that offer optimal model systems to mechanistically test the hypothesis that precursor traits increase the likelihood of convergence: (i) 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 occurred by the repeated exaptation of ancient morphogenetic programs and, in the case of yeasts, additionally, by the emergence 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. Although these are bold hypotheses, we obtained promising preliminary results that support them.

We designed an experimental plan involving phylogeny-aware comparative -omics, reverse genetics, and evo-devo, which, when combined with our preliminary results, will provide a robust entry point for 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 test if certain precursor traits can promote convergence.