De novo evolution of macroscopic multicellularity

Area of Science:

• Evolutionary Biology
• Biophysics
• Microbiology

Background:

• Multicellular lineages evolve from simple cell groups into Darwinian entities.
• The biophysical mechanisms enabling sustained multicellular evolution are poorly understood.

Purpose of the Study:

• Investigate the evolution of multicellularity using a long-term experiment with snowflake yeast (Saccharomyces cerevisiae).
• Determine the role of oxygen availability in the evolution of multicellular size and complexity.

Main Methods:

• Conducted a long-term evolution experiment selecting for larger group size in snowflake yeast.
• Utilized three metabolic treatments: anaerobic, obligately aerobic, and mixotrophic.
• Analyzed changes in size, biophysical toughness, and cellular morphology over 600 rounds of selection.

Main Results:

• Anaerobic snowflake yeast evolved to macroscopic size (mm scale), increasing in size by ~2x10^4-fold and toughness by ~10^4-fold.
• Macroscopic evolution in anaerobic conditions was driven by biophysical adaptations, including cell elongation and branch entanglement.
• Snowflake yeast under low oxygen conditions remained microscopic, showing only a sixfold increase in size.

Conclusions:

• Oxygen levels are critical for the evolution of multicellular size.
• Biophysical adaptations, such as cell elongation and entanglement, facilitate sustained multicellular evolution.
• This study provides insights into the evolutionary transition of individuality and overcoming biophysical limitations in early multicellular life.