Biology Department and Center for Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, ON, Canada
Biology Department and Center for Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, ON, Canada Department of Biology, Carleton University, Ottawa, ON, Canada.
Mol Biol Evol. 2015 Jun;32(6):1436-48. doi: 10.1093/molbev/msv033. Epub 2015 Mar 11.
Across the great diversity of life, there are many compelling examples of parallel and convergent evolution-similar evolutionary changes arising in independently evolving populations. Parallel evolution is often taken to be strong evidence of adaptation occurring in populations that are highly constrained in their genetic variation. Theoretical models suggest a few potential factors driving the probability of parallel evolution, but experimental tests are needed. In this study, we quantify the degree of parallel evolution in 15 replicate populations of Pseudomonas fluorescens evolved in five different environments that varied in resource type and arrangement. We identified repeat changes across multiple levels of biological organization from phenotype, to gene, to nucleotide, and tested the impact of 1) selection environment, 2) the degree of adaptation, and 3) the degree of heterogeneity in the environment on the degree of parallel evolution at the gene-level. We saw, as expected, that parallel evolution occurred more often between populations evolved in the same environment; however, the extent of parallel evolution varied widely. The degree of adaptation did not significantly explain variation in the extent of parallelism in our system but number of available beneficial mutations correlated negatively with parallel evolution. In addition, degree of parallel evolution was significantly higher in populations evolved in a spatially structured, multiresource environment, suggesting that environmental heterogeneity may be an important factor constraining adaptation. Overall, our results stress the importance of environment in driving parallel evolutionary changes and point to a number of avenues for future work for understanding when evolution is predictable.
在生命的多样性中，有许多引人注目的平行和趋同进化的例子——在独立进化的群体中出现相似的进化变化。平行进化通常被视为在遗传变异受到高度限制的群体中发生适应的有力证据。理论模型提出了一些潜在的因素来驱动平行进化的概率，但需要进行实验测试。在这项研究中，我们量化了在五个不同的资源类型和排列的环境中进化的 15 个重复的荧光假单胞菌种群的平行进化程度。我们从表型、基因到核苷酸的多个层次上确定了重复的变化，并测试了 1）选择环境、2）适应程度和 3）环境异质性对基因水平平行进化程度的影响。正如预期的那样，我们发现，在相同环境中进化的种群之间更经常发生平行进化；然而，平行进化的程度差异很大。适应程度并没有显著解释我们系统中平行性程度的变化，但可用有益突变的数量与平行进化呈负相关。此外，在空间结构复杂、多资源环境中进化的种群中，平行进化的程度显著更高，这表明环境异质性可能是限制适应的一个重要因素。总的来说，我们的结果强调了环境在驱动平行进化变化中的重要性，并指出了未来理解进化何时可预测的一些途径。
