Data from: Migration enhances adaptation in bacteriophage populations evolving in ecological sinks

Migration between populations can be a major evolutionary force. However, some disagreement exists as to precisely how migration affects population adaptation. Some theories emphasize the inhibitory effects of gene flow between locally adapted populations, whereas others propose that migration can enhance adaptation. Migration has also been theorized to rescue sink populations from extinction. In our experiments, we serially passaged bacteriophage Φ6 host range mutants under sink conditions on a novel host while manipulating the source and number of migrants into these experimental populations. Migrants from two sources were used: mutant Φ6 phage able to infect a novel host (treatment) and wild-type Φ6 phage unable to infect a novel host (control). We used quadratic regressions to determine the relationship between the number of migrants per passage and the absolute fitnesses of experimental populations following 30 passages. Our results showed that migration from a control population had no effect on absolute fitnesses of our serially passaged populations following 30 passages. By contrast, the relationship between migrants per passage and absolute fitnesses for populations receiving migrants able to infect the novel host was best described by an upwardly concave curve. These results suggest that intermediate levels of migration can have favorable impacts on evolutionary adaptation.

种群间的迁移是重要的进化驱动力之一。然而，学界对于迁移如何具体影响种群适应仍存在一定争议。部分理论强调局部适应种群间基因流的抑制作用，另有理论则提出迁移可促进适应过程；还有理论认为，迁移可帮助汇种群（sink population）摆脱灭绝困境。本实验中，我们在以新型宿主为唯一宿主的汇种群环境下，对Φ6噬菌体（bacteriophage Φ6）的宿主范围突变体（host range mutant）进行连续传代（serial passage）培养，并对引入各实验种群的迁移者来源与数量进行精准调控。本次实验设置两类迁移者来源：一是能够侵染新型宿主的Φ6突变噬菌体（实验组），二是无法侵染新型宿主的野生型Φ6噬菌体（对照组）。我们采用二次回归（quadratic regression）分析法，探究每代迁移者数量与经过30次传代后的实验种群绝对适合度（absolute fitness）之间的关联。实验结果显示，来自对照组种群的迁移对经30次传代的连续培养种群的绝对适合度无显著影响。与之相反，对于接收能够侵染新型宿主的迁移者的种群而言，每代迁移者数量与实验种群绝对适合度之间的关系，最优拟合模型为一条上凹曲线。上述结果表明，中等程度的迁移可对进化适应过程产生积极影响。