Presence of a loner strain maintains cooperation and diversity in well-mixed bacterial communities
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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.
Inglis , R , Biernaskie , J , Gardner , A & Kümmerli , R 2016 , ' Presence of a loner strain maintains cooperation and diversity in well-mixed bacterial communities ' Proceedings of the Royal Society B: Biological Sciences , vol 283 , no. 1822 . DOI: 10.1098/rspb.2015.2682
Proceedings of the Royal Society B: Biological Sciences
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