Weissman Maya Rochelle, Raynes Yevgeniy, Weinreich Daniel M
bioRxiv. 2024 Jan 11:2023.07.11.548608. doi: 10.1101/2023.07.11.548608.
Bet hedging is a ubiquitous strategy for risk reduction in the face of unpredictable environmental change where a lineage lowers its variance in fitness across environments at the expense of also lowering its arithmetic mean fitness. Classically, the benefit of bet hedging has been quantified using geometric mean fitness (GMF); bet hedging is expected to evolve if and only if it has a higher GMF than the wild-type. We build upon previous research on the effect of incorporating stochasticity in phenotypic distribution, environment, and reproduction to investigate the extent to which these sources of stochasticity will impact the evolution of real-world bet hedging traits. We utilize both individual-based simulations and Markov chain numerics to demonstrate that modeling stochasticity can alter the sign of selection for the bet hedger compared to deterministic predictions. We find that bet hedging can be deleterious at small population sizes and beneficial at larger population sizes. This non-monotonic dependence of the sign of selection on population size, known as sign inversion, exists across parameter space for both conservative and diversified bet hedgers. We apply our model to published data of bet hedging strategies to show that sign inversion exists for biologically relevant parameters in two study systems: Papaver dubium, an annual poppy with variable germination phenology, and Salmonella typhimurium, a pathogenic bacteria that exhibits antibiotic persistence. Taken together, our results suggest that GMF is not enough to predict when bet hedging is adaptive.
在面对不可预测的环境变化时，权衡下注是一种普遍存在的降低风险的策略，即一个谱系以牺牲其算术平均适合度为代价，降低其在不同环境下适合度的方差。传统上，权衡下注的益处是用几何平均适合度（GMF）来量化的；当且仅当权衡下注的几何平均适合度高于野生型时，它才有望进化。我们基于之前关于在表型分布、环境和繁殖中纳入随机性的影响的研究，来探究这些随机性来源在多大程度上会影响现实世界中权衡下注性状的进化。我们利用基于个体的模拟和马尔可夫链数值计算来证明，与确定性预测相比，对随机性进行建模可以改变对权衡下注者选择的符号。我们发现，在种群规模较小时，权衡下注可能是有害的，而在种群规模较大时则是有益的。选择符号对种群规模的这种非单调依赖性，即符号反转，在保守型和多样化权衡下注者的参数空间中均存在。我们将我们的模型应用于已发表的权衡下注策略数据，以表明在两个研究系统中，对于生物学相关参数存在符号反转：一种一年生罂粟——具可变萌发物候的野罂粟，以及一种表现出抗生素耐受性的病原菌——鼠伤寒沙门氏菌。综合来看，我们的结果表明，几何平均适合度不足以预测权衡下注何时具有适应性。
