Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA
Proc Biol Sci. 2018 Feb 14;285(1872). doi: 10.1098/rspb.2017.2459.
Mutations in a microbial population can increase the frequency of a genotype not only by increasing its exponential growth rate, but also by decreasing its lag time or adjusting the yield (resource efficiency). The contribution of multiple life-history traits to selection is a critical question for evolutionary biology as we seek to predict the evolutionary fates of mutations. Here we use a model of microbial growth to show that there are two distinct components of selection corresponding to the growth and lag phases, while the yield modulates their relative importance. The model predicts rich population dynamics when there are trade-offs between phases: multiple strains can coexist or exhibit bistability due to frequency-dependent selection, and strains can engage in rock-paper-scissors interactions due to non-transitive selection. We characterize the environmental conditions and patterns of traits necessary to realize these phenomena, which we show to be readily accessible to experiments. Our results provide a theoretical framework for analysing high-throughput measurements of microbial growth traits, especially interpreting the pleiotropy and correlations between traits across mutants. This work also highlights the need for more comprehensive measurements of selection in simple microbial systems, where the concept of an ordinary fitness landscape breaks down.
在微生物种群中，突变不仅可以通过提高其指数增长率来增加基因型的频率，还可以通过降低其延迟时间或调整产量（资源效率）来实现。对于进化生物学来说，多个生活史特征对选择的贡献是一个关键问题，因为我们试图预测突变的进化命运。在这里，我们使用微生物生长模型表明，选择有两个明显的组成部分，分别对应于生长和延迟阶段，而产量则调节它们的相对重要性。当相位之间存在权衡时，该模型预测会出现丰富的种群动态：由于频率依赖选择，多个菌株可以共存或表现出双稳性，并且由于非传递选择，菌株可以进行石头剪刀布相互作用。我们描述了实现这些现象所需的环境条件和特征模式，并表明这些现象很容易在实验中实现。我们的结果为分析微生物生长特征的高通量测量提供了一个理论框架，特别是解释了突变体之间特征的多效性和相关性。这项工作还强调了在简单微生物系统中需要更全面地测量选择，因为普通适应度景观的概念在这里不再适用。
