Ascensao Joao A, Lok Kristen, Hallatschek Oskar
Department of Bioengineering, University of California Berkeley, Berkeley, CA, USA.
California Institute for Quantitative Biosciences, University of California Berkeley, Berkeley, CA, USA.
Nat Ecol Evol. 2025 Jan;9(1):166-179. doi: 10.1038/s41559-024-02578-3. Epub 2024 Nov 22.
Large stochastic population abundance fluctuations are ubiquitous across the tree of life, impacting the predictability and outcomes of population dynamics. It is generally thought that abundance fluctuations with a Taylor's law exponent of two do not strongly impact evolution. However, we argue that such abundance fluctuations can lead to substantial genotype frequency fluctuations if different genotypes in a population experience these fluctuations asynchronously. By serially diluting mixtures of two closely related Escherichia coli strains, we show that such asynchrony can occur, leading to giant frequency fluctuations that far exceed expectations from genetic drift. We develop an effective model explaining that the abundance fluctuations arise from correlated offspring numbers between individuals, and the large frequency fluctuations result from (even slight) decoupling in offspring number correlations between genotypes. The model quantitatively predicts the observed abundance and frequency fluctuation scaling. Initially close trajectories diverge exponentially, suggesting that chaotic dynamics may underpin the excess frequency fluctuations. Our findings suggest that decoupling noise is also present in mixed-genotype Saccharomyces cerevisiae populations. Theoretical analyses demonstrate that decoupling noise can strongly influence evolutionary outcomes, in a manner distinct from genetic drift. Given the generic nature of these frequency fluctuations, we expect them to be widespread across biological populations.
大规模随机种群丰度波动在整个生命之树中普遍存在，影响着种群动态的可预测性和结果。一般认为，泰勒定律指数为2的丰度波动对进化的影响不大。然而，我们认为，如果种群中的不同基因型异步经历这些波动，那么这种丰度波动会导致显著的基因型频率波动。通过对两种密切相关的大肠杆菌菌株混合物进行连续稀释，我们表明这种异步现象可能会发生，从而导致巨大的频率波动，远远超过遗传漂变的预期。我们开发了一个有效模型，解释了丰度波动源于个体间相关的后代数量，而大的频率波动则源于基因型间后代数量相关性的（即使是轻微的）解耦。该模型定量预测了观察到的丰度和频率波动标度。最初接近的轨迹呈指数发散，这表明混沌动力学可能是频率波动过大的基础。我们的研究结果表明，混合基因型酿酒酵母种群中也存在解耦噪声。理论分析表明，解耦噪声能够以不同于遗传漂变的方式强烈影响进化结果。鉴于这些频率波动的普遍性，我们预计它们在生物种群中广泛存在。
