Cooperative behaviors in human, animal, and even microbial societies are vulnerable to exploitation. Kin discrimination has been hypothesized to help stabilize cooperation. However, the mechanisms that sustain cooperative behavior remain poorly understood. Here, we investigate the role of kin discrimination in limiting the spread of cheats in adjoining populations during surfactant dependent cooperative swarming over surfaces using the bacterium Bacillus subtilis as a model organism. We show that mixing surfactant secreting cooperators and cheats that do not produce surfactants at 1:1 initial ratio quickly leads to cooperation collapse. However, when such common swarms encounter non-kin B. subtilis swarms, the proportion of the surfactant non-producers decreases, suggesting that kinship dependent interactions may limit cheats’ advantage in an adjoining population. To further validate this finding, we subjected wild-type cooperators to multiple transient encounters with kin and non-kin swarms over 20 cycles of experimental evolution. The evolved populations exposed to non-kin swarms less frequently contained defective swarming phenotypes compared to those encountering kin swarms. Altogether, our results support the prediction that the spread of cheats in an adjoining bacterial population is impeded by kin discrimination interactions which might have a role in stabilizing cooperative behavior in evolving populations.

中文翻译：

---

枯草芽孢杆菌土壤分离株之间的非亲属相互作用限制了蜂群缺陷作弊的传播


人类、动物甚至微生物社会中的合作行为都容易受到利用。亲属歧视已被假设有助于稳定合作。然而，维持合作行为的机制仍然知之甚少。在这里，我们研究了在表面活性剂依赖性合作蜂群中限制作弊在相邻种群中传播的作用，使用细菌枯草芽孢杆菌作为模式生物在表面上蜂拥而至。我们表明，以 1：1 的初始比例混合分泌表面活性剂的合作者和不产生表面活性剂的作弊者会迅速导致合作崩溃。然而，当这种常见的群体遇到非亲属枯草芽孢杆菌群体时，表面活性剂非生产者的比例会降低，这表明亲缘关系依赖性相互作用可能会限制作弊者在相邻种群中的优势。为了进一步验证这一发现，我们在 20 个实验进化周期中让野生型合作者与亲属和非亲属群体进行多次瞬态相遇。与遇到亲属群的种群相比，暴露于非亲属群的进化种群较少包含有缺陷的群体表型。总而言之，我们的结果支持这样一个预测，即亲缘分辨相互作用阻碍了作弊在相邻细菌种群中的传播，这可能在稳定进化种群中的合作行为方面发挥作用。