Replaying the Evolution of Multicellularity in a Test Tube

Understanding the very first steps of how single cells evolved into multicellular organisms remains a fundamental challenge, as these events happened in the deep past. In this talk, Ozan will discuss how the Ratcliff lab studies this transition in real-time using snowflake yeast in the Multicellularity Long-Term Evolution Experiment (MuLTEE), sharing key findings and ongoing research. By lifting environmental constraints on multicellular size, microscopic ancestral yeast evolved to form remarkably tough clusters visible to the naked eye (mm-scaled), offering insights into the historical relationship between rising oxygen and the evolution of large multicellular life. This dramatic size increase came through changes in cell shape and intercellular bonds, driven by mutations in cell-cycle genes, whole-genome duplication, and sustained aneuploidies. The evolution of macroscopic size led to an entrenched multicellular state resistant to reversion to unicellularity, representing a shift in the unit of selection from cells to multicellular clusters. Overall, MuLTEE demonstrates that major evolutionary transitions can be studied experimentally, paralleling a few aspects of ancient transformations as well as exploring novel multicellular adaptations untested by natural history.

Ozan completed his BSc in Biochemistry and MS in Molecular Biology and Genetics, then moved to the Max Planck Institute for Evolutionary Biology, for his PhD studies, where he examined yeast evolutionary genetics exploring topics such as gene duplication and social adaptation in microbes, evolution of reproductive isolation and speciation, and spread of selfish genetic elements. Next, he moved to the Ratcliff Lab at Georgia Tech for his postdoctoral work, where he started an experiment to test the effect of oxygen concentration on multicellular evolution using snowflake yeast. Currently, he works as a senior research scientist at Georgia Tech leading the Multicellular Long-Term Evolution Experiment (MuLTEE). This project explores how single cells form simple multicellular clusters and evolve novel multicellular adaptations in real time over thousands of generations in the lab, allowing us to study nascent multicellularity in a genetically and phenotypically tractable eukaryotic model system. In addition to his research, he teaches undergraduate and graduate level courses at Tech.

For more information, please visit the Ratcliff Lab website.