Spatial self-organization favors heterotypic cooperation over cheating.
Spatial self-organization favors heterotypic cooperation over cheating.
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作者：
Momeni B;Waite AJ;Shou W
异型合作两个种群交换不同的利益，但生产成本很高，这种合作很普遍。骗子利用利益逃避贡献，可能会破坏合作。两种机制可以稳定异型合作。在“伙伴选择”中，合作者认识到并选择合作而不是欺骗伙伴;在“伙伴忠诚度反馈”中，来自重复互动的健康反馈确保帮助你的伙伴帮助你自己。一个促进重复互动的空间环境如何促进健康反馈？我们通过数学模型研究了这一过程，并改造了无法识别的酿酒酵母菌株。在这里，合作者和他们的异型合作伙伴（合作伙伴）交换不同的必需代谢物。作弊者利用合作伙伴产生的代谢产物没有往复，并在竞争中上级合作者。尽管最初的空间分布是随机的，但合作者比作弊者获得了更多的伙伴邻居。作弊者贡献越少，就越被排斥和不受欢迎。这种自组织，在细胞生长到开放空间的过程中，由合作者和作弊者对合作伙伴的不对称适应效应驱动，实现了分类。DOI：http://dx.doi.org/10.7554/eLife.00960.001同一物种的个体之间的合作，以及不同物种之间的合作，在进化中是非常重要的。例如，大型鱼类依靠小型清洁鱼来清除寄生虫，而小型鱼类则从这些寄生虫中获得营养。然而，合作可能会被其他个体或物种破坏，他们通过利用合作者而“欺骗”，而不提供任何回报。例如，一些清洁鱼通过咬掉宿主的健康组织来欺骗，除了寄生虫。通过分享相同利益而合作的基因相关个体可以通过给予其亲属优惠待遇（一种称为亲属歧视的过程）或与亲属保持密切关系以形成集群（亲属忠诚度）来打击作弊者。然而，两个遗传上不相关的群体通过分享不同的利益而相互合作，不能使用这些方法来克服作弊者。相反，他们依赖于伴侣的选择或伴侣忠诚度的反馈。伙伴选择--清洁鱼和它们的宿主所采用的方法--依赖于一个种群识别来自另一个种群的信号并做出相应的反应：例如，大鱼观察清洁鱼，接近那些与当前宿主合作的鱼，避开那些作弊的鱼。另一方面，伴侣忠诚度反馈依赖于两个群体之间的重复相互作用，这在进化适应性方面为双方提供了优势：例如，称为线粒体和叶绿体的细胞器生活在细胞内，帮助细胞收获能量，并在此过程中为自己和宿主细胞提供能量。在某些情况下，例如无花果和无花果黄蜂之间的合作，或者某些植物和在其根部固氮的细菌之间的合作，研究人员无法同意种群是否依赖于伴侣选择或伴侣忠诚度反馈。现在Momeni等人结合酵母实验和数学建模，更详细地探索伴侣忠诚度反馈。他们首先使用基因工程技术生产两种相互合作的酵母菌，每种酵母菌都提供一种对另一种酵母菌至关重要的代谢物，但不能相互识别：这意味着这些群体不能依靠伴侣选择来对抗作弊者。然后，Momeni等人观察了这两个物种如何相互作用，以及第三种酵母如何通过消耗其中一种代谢物而不释放自己的任何代谢物来欺骗。Momeni等人发现，只要有酵母细胞生长的空间，两种合作的物种就会自组织成混合集群，而作弊物种则被排除在这些集群之外。自组织是由一个正反馈循环驱动的，涉及两个合作的物种，每个物种都有助于增加另一个物种的适应性。Momeni等人的研究结果表明，两个基因上不相关的群体可以在不使用伙伴选择的情况下合作并对抗作弊者。DOI：http://dx.doi.org/10.7554/eLife.00960.002网站
Heterotypic cooperation—two populations exchanging distinct benefits that are costly to produce—is widespread. Cheaters, exploiting benefits while evading contribution, can undermine cooperation. Two mechanisms can stabilize heterotypic cooperation. In ‘partner choice’, cooperators recognize and choose cooperating over cheating partners; in ‘partner fidelity feedback’, fitness-feedback from repeated interactions ensures that aiding your partner helps yourself. How might a spatial environment, which facilitates repeated interactions, promote fitness-feedback? We examined this process through mathematical models and engineered Saccharomyces cerevisiae strains incapable of recognition. Here, cooperators and their heterotypic cooperative partners (partners) exchanged distinct essential metabolites. Cheaters exploited partner-produced metabolites without reciprocating, and were competitively superior to cooperators. Despite initially random spatial distributions, cooperators gained more partner neighbors than cheaters did. The less a cheater contributed, the more it was excluded and disfavored. This self-organization, driven by asymmetric fitness effects of cooperators and cheaters on partners during cell growth into open space, achieves assortment. DOI: http://dx.doi.org/10.7554/eLife.00960.001 Cooperation between individuals of the same species, and also between different species, is known to be important in evolution. Large fish, for example, rely on small cleaner fish to remove parasites, while the small fish benefit from the nutrients in these parasites. However, cooperation can be undermined by other individuals or species who “cheat” by taking advantage of those who cooperate, without providing any benefits in return. For example, some cleaner fish cheat by biting off healthy tissue from their host, in addition to parasites. Genetically-related individuals who cooperate by sharing identical benefits can combat cheaters by giving preferential treatment to their relatives (a process known as kin discrimination) or by staying close to the relatives to form clusters (kin fidelity). However, two genetically-unrelated populations that mutually cooperate by sharing different benefits cannot employ these methods to overcome cheaters. Instead they rely on either partner choice or partner fidelity feedback. Partner choice – the approach adopted by cleaner fish and their hosts – relies on one population recognizing a signal from the other population and responding accordingly: for example, large fish observe cleaner fish and approach those that cooperate with their current host and avoid those that cheat. Partner fidelity feedback, on the other hand, relies on repeated interactions between the two populations providing an advantage in terms of evolutionary fitness to both: for example, organelles called mitochondria and chloroplasts live inside cells, helping the cells to harvest energy and providing energy for themselves and the host cells in the process. In some cases – such as the cooperation between figs and fig wasps, or between certain plants and the bacteria that fix nitrogen in their roots – researchers cannot agree if the populations are relying on partner choice or partner fidelity feedback. Now Momeni et al. have used a combination of experiments on yeast and mathematical modeling to explore partner fidelity feedback in greater detail. They started by using genetic engineering techniques to produce two species of yeast that mutually cooperate, each providing a metabolite that is essential to the other, but are not able to recognize each other: this means that these populations cannot rely on partner choice to combat cheaters. Momeni et al. then observed how these two species interacted with each other and a third species of yeast that cheated by consuming one of the metabolites without releasing any metabolite of its own. Momeni et al. found that as long as there was space for the yeast cells to grow into, the two species that cooperated self-organized into mixed clusters, with the cheating species being excluded from these clusters. The self-organization was driven by a positive feedback loop involving the two species that cooperated, with each species helping to increase the fitness of the other. The results of Momeni et al. demonstrate that it is possible for two genetically unrelated populations to cooperate and combat cheaters without the use of partner choice. DOI: http://dx.doi.org/10.7554/eLife.00960.002