Amor Daniel R, Montañez Raúl, Duran-Nebreda Salva, Solé Ricard
Physics of Living Systems, Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America.
ICREA-Complex Systems Lab, Department of Experimental and Health Sciences, Universitat Pompeu Fabra, Barcelona, Spain.
PLoS Comput Biol. 2017 Aug 21;13(8):e1005689. doi: 10.1371/journal.pcbi.1005689. eCollection 2017 Aug.
A major force contributing to the emergence of novelty in nature is the presence of cooperative interactions, where two or more components of a system act in synergy, sometimes leading to higher-order, emergent phenomena. Within molecular evolution, the so called hypercycle defines the simplest model of an autocatalytic cycle, providing major theoretical insights on the evolution of cooperation in the early biosphere. These closed cooperative loops have also inspired our understanding of how catalytic loops appear in ecological systems. In both cases, hypercycle and ecological cooperative loops, the role played by space seems to be crucial for their stability and resilience against parasites. However, it is difficult to test these ideas in natural ecosystems, where time and spatial scales introduce considerable limitations. Here, we use engineered bacteria as a model system to a variety of environmental scenarios identifying trends that transcend the specific model system, such an enhanced genetic diversity in environments requiring mutualistic interactions. Interestingly, we show that improved environments can slow down mutualistic range expansions as a result of genetic drift effects preceding local resource depletion. Moreover, we show that a parasitic strain is excluded from the population during range expansions (which acknowledges a classical prediction). Nevertheless, environmental deterioration can reshape population interactions, this same strain becoming part of a three-species mutualistic web in scenarios in which the two-strain mutualism becomes non functional. The evolutionary and ecological implications for the design of synthetic ecosystems are outlined.
自然界中促成新事物出现的一股主要力量是合作性相互作用的存在，即系统中的两个或多个组成部分协同作用，有时会导致更高级别的涌现现象。在分子进化中，所谓的超循环定义了自催化循环的最简单模型，为早期生物圈中合作的进化提供了重要的理论见解。这些封闭的合作环也启发了我们对催化环在生态系统中如何出现的理解。在超循环和生态合作环这两种情况下，空间所起的作用似乎对它们的稳定性和抵御寄生虫的能力至关重要。然而，在自然生态系统中很难验证这些观点，因为时间和空间尺度带来了相当大的限制。在这里，我们使用工程细菌作为模型系统来研究各种环境情景，识别超越特定模型系统的趋势，比如在需要互利相互作用的环境中增强的遗传多样性。有趣的是，我们表明，由于局部资源耗尽之前的遗传漂变效应，改善的环境会减缓互利范围的扩展。此外，我们表明，在范围扩展过程中，一种寄生菌株会被种群排除（这证实了一个经典预测）。然而，环境恶化会重塑种群相互作用，在两菌株互利共生变得不起作用的情景中，同一菌株会成为三物种互利网络的一部分。文中概述了对合成生态系统设计的进化和生态影响。
