Nonadaptive processes can create the appearance of facultative cheating in microbes

Area of Science:

• Evolutionary biology
• Microbial ecology
• Behavioral ecology

Background:

• Social life in microbes like Myxococcus bacteria and Dictyostelium amoebae can involve cooperation and exploitation.
• Observed competitive advantages in mixed-genotype microbial groups are often attributed to facultative cheating.
• These microbial social dynamics are well-studied in evolutionary biology.

Purpose of the Study:

• To investigate an alternative explanation for competitive dynamics in social microbes.
• To differentiate between adaptive cheating and non-adaptive scenarios driven by mutations.
• To explore the role of kin selection and local competition in microbial social evolution.

Main Methods:

• Development of simple mathematical models to simulate microbial interactions.
• Analysis of fitness effects of mutations within social groups and in mixed-genotype settings.
• Consideration of factors like local resource competition and mutation accumulation.

Main Results:

• Observations of microbial competition in mixed-genotype groups are consistent with kin selection-mutation balance, not just adaptive cheating.
• Deleterious mutations reducing within-group competitiveness (e.g., delayed sporulation in Myxococcus) can manifest fitness differences only in the presence of other strains.
• Local competition can generate costs and benefits in Hamilton's rule even without cooperative traits.

Conclusions:

• Deleterious mutations can significantly impact social dynamics and competition in large microbial populations.
• The accumulation of mutations under relaxed within-group selection can mimic adaptive social strategies.
• Further research is needed to distinguish evolutionary causes of microbial social competition.