Department of Plant and Microbial Biology, University of Zurich, Zurich, Switzerland.
Department of Quantitative Biomedicine, University of Zurich, Zurich, Switzerland.
J Evol Biol. 2019 May;32(5):412-424. doi: 10.1111/jeb.13423. Epub 2019 Feb 25.
Policing occurs in insect, animal and human societies, where it evolved as a mechanism maintaining cooperation. Recently, it has been suggested that policing might even be relevant in enforcing cooperation in much simpler organisms such as bacteria. Here, we used individual-based modelling to develop an evolutionary concept for policing in bacteria and identify the conditions under which it can be adaptive. We modelled interactions between cooperators, producing a beneficial public good, cheaters, exploiting the public good without contributing to it, and public good-producing policers that secrete a toxin to selectively target cheaters. We found that toxin-mediated policing is favoured when (a) toxins are potent and durable, (b) toxins are cheap to produce, (c) cell and public good diffusion is intermediate, and (d) toxins diffuse farther than the public good. Although our simulations identify the parameter space where toxin-mediated policing can evolve, we further found that policing decays when the genetic linkage between public good and toxin production breaks. This is because policing is itself a public good, offering protection to toxin-resistant mutants that still produce public goods, yet no longer invest in toxins. Our work thus highlights that not only specific environmental conditions are required for toxin-mediated policing to evolve, but also strong genetic linkage between the expression of public goods, toxins and toxin resistance is essential for this mechanism to remain evolutionarily stable in the long run.
policing 存在于昆虫、动物和人类社会中，它作为一种维持合作的机制而进化。最近，有人提出，即使在细菌等更简单的生物中，policing 也可能与执行合作有关。在这里，我们使用基于个体的建模方法，为细菌中的 policing 建立了一个进化概念，并确定了它具有适应性的条件。我们模拟了合作者之间的相互作用，产生有益的公共利益，骗子，利用公共利益而不贡献，以及生产毒素选择性针对骗子的公共利益生产者。我们发现，当（a）毒素有效且持久，（b）毒素生产成本低廉，（c）细胞和公共利益扩散处于中间水平，（d）毒素扩散距离超过公共利益时，毒素介导的 policing 是有利的。虽然我们的模拟确定了可以进化的毒素介导 policing 参数空间，但我们进一步发现，当公共利益和毒素生产之间的遗传联系破裂时，policing 会衰减。这是因为 policing 本身就是一种公共利益，为仍然产生公共利益但不再投资于毒素的毒素抗性突变体提供保护，但不再投资于毒素。因此，我们的工作强调，不仅需要特定的环境条件才能使毒素介导的 policing 进化，而且还需要公共利益、毒素和毒素抗性的表达之间的强遗传联系，以使这种机制在长期内保持进化稳定。
