Mutualisms occur when at least two species provide a net fitness benefit to each other. These types of interactions are ubiquitous in nature, with more being discovered regularly. Mutualisms are vital to humankind: Pollinators and soil microbes are critical in agriculture, bacterial microbiomes regulate our health, and domesticated animals provide us with food and companionship. Many hypotheses exist on how mutualisms evolve; however, they are difficult to evaluate without bias, due to the fragile and idiosyncratic systems most often investigated. Instead, we have created an artificial life simulation, Symbulation, which we use to examine mutualism evolution based on (1) the probability of vertical transmission (symbiont being passed to offspring) and (2) the spatial structure of the environment. We found that spatial structure can lead to less mutualism at intermediate vertical transmission rates. We provide evidence that this effect is due to the ability of quasi species to purge parasites, reducing the diversity of available symbionts. Our simulation is easily extended to test many additional hypotheses about the evolution of mutualism and serves as a general model to quantitatively compare how different environments affect the evolution of mutualism.

中文翻译：

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空间结构会减少共生合作

当至少两个物种相互提供净健康益处时，就会发生互惠互利。这些类型的相互作用在自然界中无处不在，并且经常被发现。互惠对人类至关重要：传粉媒介和土壤微生物对农业至关重要，细菌微生物群落调节我们的健康，驯养动物为我们提供食物和陪伴。关于互惠互利如何演变存在许多假设；然而，由于最常研究的脆弱和特殊系统，它们很难不带偏见地进行评估。相反，我们创建了一个人工生命模拟，Symbulation，我们用它来检查基于 (1) 垂直传播的概率（共生体传递给后代）和 (2) 环境的空间结构的共生进化。我们发现空间结构在中等垂直传输率下会导致更少的共生。我们提供的证据表明，这种影响是由于准物种清除寄生虫的能力，减少了可用共生体的多样性。我们的模拟很容易扩展到测试关于共生进化的许多其他假设，并作为一个通用模型来定量比较不同环境如何影响共生进化。