Department of Biology, University of Alabama at Birmingham, Birmingham, AL 35294.
BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, MI 48824.
Proc Natl Acad Sci U S A. 2021 Sep 28;118(39). doi: 10.1073/pnas.2109813118.
Many biological functions are leaky, and organisms that perform them contribute some of their products to a community "marketplace" in which nonperforming individuals may compete for them. Leaky functions are partitioned unequally in microbial communities, and the evolutionary forces determining which species perform them and which become beneficiaries are poorly understood. Here, we demonstrate that the market principle of comparative advantage determines the distribution of a leaky antibiotic resistance gene in an environment occupied by two "species"-strains of growing on mutually exclusive resources and thus occupying separate niches. Communities comprised of antibiotic-resistant cells were rapidly invaded by sensitive cells of both types. While the two phenotypes coexisted stably for 500 generations, in 15/18 replicates, antibiotic sensitivity became fixed in one species. Fixation always occurred in the same species despite both species being genetically identical except for their niche-defining mutation. In the absence of antibiotic, the fitness cost of resistance was identical in both species. However, the intrinsic resistance of the species that ultimately became the sole helper was significantly lower, and thus its reward for expressing the resistance gene was higher. Opportunity cost of resistance, not absolute cost or efficiency of antibiotic removal, determined which species became the helper, consistent with the economic theory of comparative advantage. We present a model that suggests that this market-like dynamic is a general property of Black Queen systems and, in communities dependent on multiple leaky functions, could lead to the spontaneous development of an equitable and efficient division of labor.
许多生物功能是有渗漏的，执行这些功能的生物体将其部分产物贡献给一个“市场”，在这个市场中，非执行者可能会争夺这些产物。微生物群落中渗漏功能的分配是不平等的，决定哪些物种执行这些功能以及哪些物种成为受益者的进化力量还知之甚少。在这里，我们证明了比较优势的市场原则决定了一个渗漏抗生素耐药基因在由两种“物种”占据的环境中的分布，这两种“物种”在相互排斥的资源上生长，从而占据了不同的生态位。由耐药细胞组成的群落很快就被两种类型的敏感细胞入侵。虽然这两种表型在 500 代内稳定共存，但在 15/18 次重复中，抗生素敏感性在一种物种中固定下来。尽管两种物种除了决定其生态位的突变外，在基因上完全相同，但固定总是发生在同一物种中。在没有抗生素的情况下，两种物种的耐药性代价是相同的。然而，最终成为唯一帮助者的物种的固有耐药性要低得多，因此它表达耐药基因的回报要高。耐药的机会成本，而不是绝对成本或抗生素去除效率，决定了哪种物种成为帮助者，这与比较优势的经济理论一致。我们提出了一个模型，表明这种类似市场的动态是黑皇后系统的普遍特性，并且在依赖多种渗漏功能的群落中，可能导致公平和高效的分工的自发发展。
