Presence of a loner strain maintains cooperation and diversity in well-mixed bacterial communities

Robert Inglis, Jay Biernaskie, Andy Gardner, Rolf Kümmerli

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28 Citations (Scopus)
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Cooperation and diversity abound in nature despite cooperators risking exploitation from defectors and superior competitors displacing weaker ones. Understanding the persistence of cooperation and diversity is therefore a major problem for evolutionary ecology, especially in the context of well-mixed populations, where the potential for exploitation and displacement is greatest. Here we demonstrate that a “loner effect”, described by economic game theorists, can maintain cooperation and diversity in real-world biological settings. We use mathematical models of public-good-producing bacteria to show that the presence of a loner strain, which produces an independent but relatively inefficient good, can lead to rock-paper-scissor dynamics, whereby cooperators outcompete loners, defectors outcompete cooperators, and
loners outcompete defectors. These model predictions are supported by our observations of evolutionary dynamics in well-mixed experimental communities of the bacterium Pseudomonas aeruginosa. We find that the coexistence of cooperators and defectors, which respectively produce and exploit the iron-scavenging siderophore pyoverdine, is stabilized by the presence of loners with an independent iron-uptake mechanism. Our results establish the loner effect as a simple and general driver of cooperation and diversity in environments that
40 would otherwise favour defection and the erosion of diversity.

Original languageEnglish
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1822
Publication statusPublished - 13 Jan 2016


  • Experimental evolution
  • Microbial biodiversity
  • Non-transitive competition
  • Rock-paper-scissors dynamics
  • Siderophore
  • Social evolution

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