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

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 Pseudomon...

尽管合作者面临背叛者的剥削风险，优势竞争者亦会排挤弱势个体，但自然界中合作与多样性依然广泛存在。因此，阐明合作与多样性的维持机制是进化生态学的核心难题之一，在充分混合种群（well-mixed populations）中尤为如此——这类环境下剥削与排挤的发生概率最高。本研究证实，经济博弈理论家所描述的孤立体效应（loner effect），可在真实生物环境中维持合作与多样性。我们以生产公共物品（public good）的细菌为对象构建数学模型，结果显示：携带可独立产生公共物品但效率相对低下的孤立体菌株，能够引发石头剪刀布式循环竞争动态，即合作者排挤孤立体，背叛者排挤合作者，而孤立体排挤背叛者。上述模型预测得到了我们在充分混合的假单胞菌（Pseudomonas）实验群落中观察到的进化动态的支持。