Laboratory Selection Quickly Erases Historical Differentiation

The roles of history, chance and selection have long been debated in evolutionary biology. Though uniform selection is expected to lead to convergent evolution between populations, contrasting histories and chance events might prevent them from attaining the same adaptive state, rendering evolution somewhat unpredictable. The predictability of evolution has been supported by several studies documenting repeatable adaptive radiations and convergence in both nature and laboratory. However, other studies suggest divergence among populations adapting to the same environment. Despite the relevance of this issue, empirical data is lacking for real-time adaptation of sexual populations with deeply divergent histories and ample standing genetic variation across fitness-related traits. Here we analyse the real-time evolutionary dynamics of Drosophila subobscura populations, previously differentiated along the European cline, when colonizing a new common environment. By analysing several life-history, physiological and morphological traits, we show that populations quickly converge to the same adaptive state through different evolutionary paths. In contrast with other studies, all analysed traits fully converged regardless of their association with fitness. Selection was able to erase the signature of history in highly differentiated populations after just a short number of generations, leading to consistent patterns of convergent evolution.进化生物学领域中，历史因素、随机偶然事件与选择作用三者的相对地位长期以来一直是学界热议的议题。尽管定向选择被认为会导致不同种群间的趋同演化，但迥异的演化历史与随机事件可能会阻碍它们达成一致的适应状态，使得演化过程具备一定的不可预测性。已有多项研究在自然与实验室环境中记录到可重复的适应辐射与趋同演化现象，为演化的可预测性提供了支持。但另有研究表明，即便在相同环境下适应的种群间也会出现分化。尽管该议题具备重要研究价值，但针对演化历史差异显著、且在适合度相关性状上拥有充足现存遗传变异的有性种群，其实时适应过程的实证数据仍较为匮乏。本研究针对曾沿欧洲渐变群产生分化的暗果蝇（Drosophila subobscura）种群，分析其在入侵全新统一环境时的实时演化动态。通过对多项生活史、生理与形态性状的分析，我们发现不同种群可通过不同演化路径，快速趋同至一致的适应状态。与此前多数研究不同的是，本研究中所有分析的性状均实现了完全趋同，无论其是否与适合度相关。仅经过数代繁衍，选择作用即可消除高度分化种群中遗留的历史演化印记，最终形成一致的趋同演化格局。