As selection frequently favors noncooperating defectors in mixed populations with cooperators, mechanisms that promote cooperation stability clearly exist. One potential mechanism is bacterial cell-to-cell communication, quorum sensing (QS), which can allow cooperators to prevent invasion by defectors. However, the impact of QS on widespread maintenance of cooperation in well-mixed conditions has not been experimentally demonstrated over extended evolutionary timescales. Here, we use wild-type (WT) Vibrio campbellii that regulates cooperation with QS and an unconditional cooperating (UC) mutant to examine the evolutionary origins and dynamics of novel defectors during a long-term evolution experiment. We found that UC lineages were completely outcompeted by defectors, whereas functioning QS enabled the maintenance of cooperative variants in most WT populations. Sequencing evolved populations revealed multiple luxR mutations that swept the UC lineages. However, the evolution of mutant lineages with reduced levels of bioluminescence (dims) occurred in many WT lineages. These dim variants also decreased other cooperative phenotypes regulated by QS, including protease production, indicating they result from changes to QS regulation. This diminished investment phenotype optimizes a tradeoff between cooperative input and growth output and suggests that decreasing the cost of QS could be a favorable strategy for maintaining the cooperative behaviors it regulates.

由于选择经常有利于与合作者混合的种群中不合作的叛逃者，因此显然存在促进合作稳定性的机制。一种潜在的机制是细菌细胞间通讯，群体感应 (QS)，它可以让合作者防止叛逃者入侵。然而，QS 对在良好混合条件下广泛维持合作的影响尚未在延长的进化时间尺度上通过实验证明。在这里，我们使用野生型 (WT)坎氏弧菌调节与 QS 和无条件合作 (UC) 突变体的合作，以在长期进化实验中检查新叛逃者的进化起源和动力学。我们发现 UC 谱系完全被叛逃者击败，而功能正常的 QS 能够在大多数 WT 人群中维持合作变体。对进化种群进行测序显示多个luxR席卷 UC 谱系的突变。然而，生物发光 (dims) 水平降低的突变谱系的进化发生在许多 WT 谱系中。这些暗淡的变体还减少了由 QS 调节的其他合作表型，包括蛋白酶的产生，表明它们是由 QS 调节的变化引起的。这种减少的投资表型优化了合作投入和增长产出之间的权衡，并表明降低 QS 的成本可能是维持其调节的合作行为的有利策略。