Department of Biological Sciences, Stanford University, California 94305-5020, USA.
Genetics. 2009 Aug;182(4):1159-64. doi: 10.1534/genetics.109.103333. Epub 2009 May 27.
Uncertain environments pose a tremendous challenge to populations: The selective pressures imposed by the environment can change so rapidly that adaptation by mutation alone would be too slow. One solution to this problem is given by the phenomenon of stochastic phenotype switching, which causes genetically uniform populations to be phenotypically heterogenous. Stochastic phenotype switching has been observed in numerous microbial species and is generally assumed to be an adaptive bet-hedging strategy to anticipate future environmental change. We use an explicit population genetic model to investigate the evolutionary dynamics of phenotypic switching rates. We find that whether or not stochastic switching is an adaptive strategy is highly contingent upon the fitness landscape given by the changing environment. Unless selection is very strong, asymmetric fitness landscapes-where the cost of being maladapted is not identical in all environments-strongly select against stochastic switching. We further observe a threshold phenomenon that causes switching rates to be either relatively high or completely absent, but rarely intermediate. Our finding that marginal changes in selection pressures can cause fundamentally different evolutionary outcomes is important in a wide range of fields concerned with microbial bet hedging.
环境施加的选择压力变化如此之快，以至于仅通过突变进行适应将过于缓慢。解决这个问题的一个方法是由随机表型切换现象提供的，该现象导致遗传上均匀的种群表现出表型异质性。在许多微生物物种中已经观察到随机表型切换，并且通常被认为是一种适应的赌注避险策略，以预测未来的环境变化。我们使用一个明确的群体遗传模型来研究表型切换率的进化动态。我们发现，随机切换是否是一种适应性策略高度取决于变化环境给出的适应度景观。除非选择非常强烈，否则不对称的适应度景观——在所有环境中适应不良的代价都不相同——强烈选择反对随机切换。我们进一步观察到一个阈值现象，导致切换率要么相对较高，要么完全不存在，但很少是中间的。我们发现，选择压力的微小变化可能导致根本不同的进化结果，这在与微生物赌注避险相关的广泛领域中非常重要。
