Evolutionary dynamics of nascent multicellular lineages.

Area of Science:

• Evolutionary biology
• Microbial evolution
• Origin of multicellularity

Background:

• Multicellularity arises from cellular collectives acting as units of selection.
• Heritable fitness variance in collectives is driven by ecological conditions.
• Reliable transitions between soma- and germ-like stages are key for lineage persistence.

Purpose of the Study:

• Investigate the adaptive significance of switching between life cycle phases in experimental bacterial collectives.
• Analyze the evolutionary dynamics under varying selective pressures on the soma-like phase.
• Explore the de novo evolution of switching mechanisms.

Main Methods:

• Propagating bacterial lineages for 10 generations under different selective regimes.
• Utilizing a control group where phase switching was abolished.
• Employing a new computational pipeline (colgen) for visualizing evolutionary dynamics and analyzing mutations.

Main Results:

• The capacity to switch between life cycle phases was central to maintaining collective fitness.
• In a non-switch treatment, mutL-dependent switching evolved de novo.
• The colgen pipeline provided visual evidence of evolutionary processes and identified key adaptive mutations.

Conclusions:

• Switching between life cycle stages is a critical mechanism for collective adaptation.
• Genealogy-centered approaches offer valuable insights into lineage-level selection.
• Understanding these dynamics sheds light on the evolution of multicellularity.