Evolutionary consequences of nascent multicellular life cycles.

Area of Science:

• Evolutionary biology
• Microbiology
• Genetics

Background:

• The transition to multicellularity requires groups to act as adaptive individuals.
• Clonal development is hypothesized to facilitate this transition, but empirical tests are lacking.
• Yeast models offer a system to study the evolution of multicellularity.

Purpose of the Study:

• To experimentally test the role of clonal development in the evolution of multicellularity.
• To compare evolutionary dynamics between clonal and aggregative yeast life cycles.
• To investigate the level of selection (cell vs. group) in early multicellular evolution.

Main Methods:

• Evolving replicate populations of snowflake yeast (clonal) and floc yeast (aggregative).
• Implementing daily selection for rapid growth (cell division) and rapid sedimentation (group size).
• Utilizing genome sequencing and mathematical modeling to analyze evolutionary changes.

Main Results:

• Both yeast types adapted, showing increased growth and survival.
• Snowflake yeast primarily gained fitness through improved group-level traits (group survival).
• Floc yeast primarily gained fitness through increased cell growth, indicating cell-level selection.

Conclusions:

• Clonal life cycles promote the evolution of Darwinian individuality at the group level.
• Early multicellular life cycles critically influence the trajectory of adaptation.
• Genetic drift, amplified by clonal bottlenecks, has complex implications for multicellular evolution.