Exclusion rules, bottlenecks and the evolution of stochastic phenotype switching
Exclusion rules, bottlenecks and the evolution of stochastic phenotype switching
复制标题
DOI：
10.1098/rspb.2011.0146
复制
发表时间：
2011-12-07
影响因子：
4.7
通讯作者：
Rainey, Paul B.
中科院分区：
文献类型：
--
作者：
Libby, Eric;Rainey, Paul B.
随机表型转换--通常被认为是一种更好的对冲或降低风险的策略--可以提高在波动环境中生存的可能性。最近的一项实验通过显示在捕捉宿主免疫反应的基本特征的选择性制度下繁殖的细菌种群中的开关的从头进化，为适应性起源提供了直接证据。该制度涉及通过双重实施排除规则和种群瓶颈实现的强频率依赖选择。在环境间转移点应用时，当前环境中常见的表型被赋予零适应度，因此被排除在参加下一轮比赛之外(排除规则)。此外，也是在转移时，为了找到下一轮选择，从幸存者中随机选择了一个表型不同的类型(瓶颈)。在这个实验的激励下，我们开发了一个数学模型来探索选择性制度的关键特征的更广泛的意义。通过分析和数值结果的结合，我们证明了排斥规则和种群瓶颈作为随机表型转换的有效选择性因子，使得即使在最初很罕见的情况下，当转换产生马尔萨斯适应度的代价时，具有转换能力的生物可以入侵非转换的种群并取代非转换类型。仿真结果表明，我们的发现对切换率、排除保真度、瓶颈大小、环境状态持续时间和增长率的变化具有很强的稳健性。我们还展示了我们的模型与一系列生物学场景的相关性，例如细菌持久性和性的进化。
Stochastic phenotype switching-often considered a bet hedging or risk-reducing strategy-can enhance the probability of survival in fluctuating environments. A recent experiment provided direct evidence for an adaptive origin by showing the de novo evolution of switching in bacterial populations propagated under a selective regime that captured essential features of the host immune response. The regime involved strong frequency-dependent selection realized via dual imposition of an exclusion rule and population bottleneck. Applied at the point of transfer between environments, the phenotype common in the current environment was assigned a fitness of zero and was thus excluded from participating in the next round (the exclusion rule). In addition, also at the point of transfer, and so as to found the next bout of selection, a single phenotypically distinct type was selected at random from among the survivors (the bottleneck). Motivated by this experiment, we develop a mathematical model to explore the broader significance of key features of the selective regime. Through a combination of analytical and numerical results, we show that exclusion rules and population bottlenecks act in tandem as potent selective agents for stochastic phenotype switching, such that even when initially rare, and when switching engenders a cost in Malthusian fitness, organisms with the capacity to switch can invade non-switching populations and replace non-switching types. Simulations demonstrate the robustness of our findings to alterations in switching rate, fidelity of exclusion, bottleneck size, duration of environmental state and growth rate. We also demonstrate the relevance of our model to a range of biological scenarios such as bacterial persistence and the evolution of sex.