The path to re-evolve cooperation is constrained in Pseudomonas aeruginosa

Area of Science:

• Microbiology
• Evolutionary Biology
• Behavioral Ecology

Background:

• Bacterial cooperation often involves secreting public goods like pyoverdine.
• Cheaters can exploit cooperation, leading to questions about cooperation's evolutionary stability.
• The ability of cheaters to revert to cooperation under changing conditions is poorly understood.

Purpose of the Study:

• To investigate if experimentally evolved bacterial cheats can re-evolve cooperation.
• To determine the conditions under which cooperation might re-emerge in a population of cheaters.
• To understand the evolutionary constraints on reverting from cheating to cooperation.

Main Methods:

• Experimental evolution of Pseudomonas aeruginosa cheats.
• Screening of evolved clones for changes in pyoverdine production.
• Testing evolved clones under conditions known to favor cooperation.

Main Results:

• No re-evolution of full cooperation was observed in evolved cheats.
• Conditions favoring cooperation (spatial structure, reduced cost) did not induce reversion.
• Complete loss of pyoverdine production was selected for in some environments.
• Trait degradation was driven by "cheating on cheats" and selection against superfluous traits.

Conclusions:

• The re-evolution of public-goods cooperation in bacteria can be evolutionarily constrained.
• Limited mutational pathways or stringent selection for revertant spread may explain the lack of reversion.
• Once established, cheating may be a more stable evolutionary outcome than cooperation.