Data from: 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 Pseudomonas aeruginosa. We find that the coexistence of cooperators and defectors that produce and exploit, respectively, 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 would otherwise favour defection and the erosion of diversity.尽管合作者面临背叛者的剥削风险，且优势竞争者会排挤弱势个体，但自然界中合作与多样性依然普遍存在。因此，解析合作与多样性的维持机制是进化生态学领域的一大核心难题，在充分混合种群中这一问题尤为突出——这类种群中剥削与排挤的可能性最高。本研究证实，经济博弈论学者提出的「孤独者效应（loner effect）」可在真实生物环境中维持合作与多样性。我们基于生产公共物品的细菌构建数学模型，结果显示：携带独立合成但效率相对较低公共物品的孤独者菌株，可引发石头剪刀布式循环竞争动态（rock-paper-scissor dynamics）——即合作者排挤孤独者，背叛者排挤合作者，而孤独者排挤背叛者。上述模型预测得到了我们在充分混合的铜绿假单胞菌（Pseudomonas aeruginosa）实验群落中观察到的进化动态的验证。我们发现，分别合成并利用夺铁型铁载体pyoverdine（绿脓杆菌素）的合作者与背叛者的共存状态，可因携带独立铁摄取机制的孤独者菌株而得到稳定。本研究结果表明，在原本会助长背叛、侵蚀多样性的环境中，孤独者效应是维持合作与多样性的简洁且普适性驱动因素。