The Multicellularity Long-Term Evolution Experiment

Official Website of the MuLTEE Project

The MuLTEE is a multi-decade experiment examining how simple groups of cells evolve into complex, functionally integrated multicellular organisms. Using snowflake yeast (Saccharomyces cerevisiae), we study the evolutionary transition to multicellularity in real time, tracking genetic, cellular, and multicellular-level changes across thousands of generations.

This website provides key information about the science behind the MuLTEE and makes data and strains from the project publicly available to researchers worldwide. Our goal is to foster a community of scientists working on the evolutionary transition to multicellularity.

Supported by NSF's Long-Term Research in Environmental Biology (LTREB) program, Award #2424492.

Treatment Groups

PO1-5

Obligately Aerobic

Grown on YEP-glycerol, which can only be respired. These populations led to the discovery that multicellularity drives ecological diversification: small and large cluster-forming lineages convergently evolved and coexisted for over 4,300 generations through oxygen-mediated growth-survival trade-offs.

PA1-5

Anaerobic

Petite mutants with mtDNA deletions, grown on YEP-dextrose. Unable to respire, these populations are unconstrained by oxygen limitation. They evolved macroscopic size (visible to the naked eye) and extensive aneuploidy, and now show near-complete deletion of the mitochondrial genome.

PM1-5

Mixotrophic

Grown on YEP-dextrose with functional mitochondria, using both fermentation and respiration. These populations remained microscopic throughout the experiment and serve as controls, retaining the capacity to revert to unicellularity even after 5,000+ generations.

Current Research Priorities (2025–2035)

Origin of Cellular Differentiation How transcriptionally-regulated cell types evolve from homogeneous ancestors

Synchronized Cell Division Evolution of developmental timing and its role in multicellular patterning

Multicellular Entrenchment How cells lose the ability to revert to unicellularity

Germ-Soma Specialization Biophysical origins of reproductive division of labor via entanglement

Whole Genome Duplication De novo evolution and long-term maintenance of polyploidy

Overcoming Diffusion Limits Self-induced fluid flows enabling exponential growth at macroscopic scales

Symmetry-Breaking Morphologies Evolution of toroidal shapes from spherical ancestors

Mitochondrial Reductive Evolution Real-time tracking of organelle genome loss in anaerobic populations

Resources

We freely share strains from our frozen archive with researchers worldwide. Visit our Data & Strains page to request strains, access genome sequences, and find protocols for working with snowflake yeast.