Social strife in the microbial world

The natural life histories of microorganisms involve complex social interactions that occur both within and between species and can be either competitive or cooperative. Flourishing research on biofilms and quorum-sensing systems has heightened interest in how and when microbes cooperate to obtain group-specific fitness advantages. However, 'cheaters' can disrupt cooperative systems by unfairly procuring an excessive share of group-generated resources while making disproportionately small contributions. Evolutionary theory predicts that such 'selfish' genotypes should readily invade cooperative populations in the absence of mechanisms to exclude them. Recent studies reviewed here have revealed selfish strategies that undermine cooperative behaviour across a variety of microbial systems, including eukaryotic slime moulds, bacteria and viruses. Further empirical understanding of microbial cheating will provide insight into the limits on cooperative behaviours and the hurdles to transitions from unicellularity to multicellularity.