Department of Biology, Queens College, Flushing, NY 11358, USA.
Evolution. 2013 Jan;67(1):10-7. doi: 10.1111/j.1558-5646.2012.01742.x. Epub 2012 Aug 10.
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.
种群间的迁移可能是一种主要的进化力量。然而，对于迁移究竟如何影响种群适应的问题，存在一些分歧。一些理论强调了局部适应种群间基因流动的抑制作用，而另一些理论则认为迁移可以增强适应。迁移也被认为可以拯救处于灭绝边缘的汇种群。在我们的实验中，我们在新宿主上的汇条件下连续传代噬菌体 Φ6 宿主范围突变体，同时操纵进入这些实验种群的移民的来源和数量。使用了两种来源的移民：能够感染新宿主的突变型 Φ6 噬菌体（处理）和不能感染新宿主的野生型 Φ6 噬菌体（对照）。我们使用二次回归来确定在 30 次传代后，每个传代的移民数量与实验种群的绝对适应度之间的关系。我们的结果表明，在 30 次传代后，来自对照种群的迁移对我们连续传代的种群的绝对适应度没有影响。相比之下，对于接受能够感染新宿主的移民的种群，移民数量与绝对适应度之间的关系最好用向上凹的曲线来描述。这些结果表明，中等水平的迁移可以对进化适应产生有利的影响。
