Data from: From nature to the lab: the impact of founder effects in adaptation

Most founding events entail a reduction of population size, which in turn leads to genetic drift effects that can deplete alleles. Besides reducing neutral genetic variability, founder effects can in principle shift additive genetic variance for phenotypes that underlie fitness. This could then lead to different rates of adaptation among populations that have undergone a population size bottleneck as well as an environmental change, even when these populations have a common evolutionary history. Thus theory suggests that there should be an association between observable genetic variability for both neutral markers and phenotypes related to fitness. Here we test this scenario by monitoring the early evolutionary dynamics of six laboratory foundations derived from founders taken from the same source natural population of Drosophila subobscura. Each foundation was in turn three-fold replicated. During their first few generations, these six foundations showed an abrupt increase in their genetic differentiation, within and between foundations. The eighteen populations that were monitored also differed in their patterns of phenotypic adaptation according to their immediately ancestral founding sample. Differences in early genetic variability and in effective population size were found to predict differences in rate of adaptation during the first 21 generations of laboratory evolution. We show that evolution in a novel environment is strongly contingent not only on the initial composition of a newly-founded population but also on the stochastic changes which occur during the first generations of colonization. Such effects make laboratory populations poor guides to the evolutionary genetic properties of their ancestral wild populations.

绝大多数奠基事件均会导致种群规模缩减，进而引发遗传漂变（genetic drift）效应，该效应可造成等位基因（alleles）的耗竭。除降低中性遗传变异（neutral genetic variability）水平外，奠基效应（founder effects）理论上还可改变调控适合度（fitness）相关表型的加性遗传方差（additive genetic variance）。即便种群拥有共同的演化历史，经历过种群瓶颈（population size bottleneck）与环境变化的不同种群间，也可能因此出现不同的适应速率。据此理论预测，中性标记（neutral markers）与适合度相关表型的可观测遗传变异之间应存在关联。本研究以取自同一自然源种群的暗果蝇（Drosophila subobscura）亲本构建6个实验室奠基种群，并对其早期演化动态进行监测，以此检验上述理论假设；每个奠基种群均设置三重重复。在初代的数代繁衍过程中，这6个奠基种群内部以及种群间的遗传分化（genetic differentiation）均出现显著跃升。被监测的18个种群的表型适应（phenotypic adaptation）模式，也因各自近祖奠基样本的差异而有所不同。研究发现，早期遗传变异水平与有效种群大小（effective population size）的差异，可预测实验室演化前21代中的适应速率差异。本研究证实，新环境下的演化过程不仅强烈依赖于新建种群的初始组成，还与定殖（colonization）初期发生的随机变化密切相关。这类效应使得实验室种群无法准确反映其野生祖先种群的演化遗传特性。