Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218.
Department of Physics, Institute for Fundamental Science, University of Oregon, Eugene, OR 97403.
Proc Natl Acad Sci U S A. 2024 Aug 20;121(34):e2411487121. doi: 10.1073/pnas.2411487121. Epub 2024 Aug 13.
When biological populations expand into new territory, the evolutionary outcomes can be strongly influenced by genetic drift, the random fluctuations in allele frequencies. Meanwhile, spatial variability in the environment can also significantly influence the competition between subpopulations vying for space. Little is known about the interplay of these intrinsic and extrinsic sources of noise in population dynamics: When does environmental heterogeneity dominate over genetic drift or vice versa, and what distinguishes their population genetics signatures? Here, in the context of neutral evolution, we examine the interplay between a population's intrinsic, demographic noise and an extrinsic, quenched random noise provided by a heterogeneous environment. Using a multispecies Eden model, we simulate a population expanding over a landscape with random variations in local growth rates and measure how this variability affects genealogical tree structure, and thus genetic diversity. We find that, for strong heterogeneity, the genetic makeup of the expansion front is to a great extent predetermined by the set of fastest paths through the environment. The landscape-dependent statistics of these optimal paths then supersede those of the population's intrinsic noise as the main determinant of evolutionary dynamics. Remarkably, the statistics for coalescence of genealogical lineages, derived from those deterministic paths, strongly resemble the statistics emerging from demographic noise alone in uniform landscapes. This cautions interpretations of coalescence statistics and raises new challenges for inferring past population dynamics.
当生物种群扩展到新的领域时，进化结果可能会受到遗传漂变的强烈影响，即等位基因频率的随机波动。同时，环境的空间变异性也会显著影响争夺空间的亚种群之间的竞争。关于这些内在和外在噪声源在种群动态中的相互作用，我们知之甚少：环境异质性何时会超过遗传漂变，或者反之，它们的种群遗传学特征有何区别？在这里，在中性进化的背景下，我们研究了种群内在的、人口统计学噪声与外在的、由异质环境提供的淬火随机噪声之间的相互作用。我们使用多物种 Eden 模型模拟了一个在局部增长率随机变化的景观上扩张的种群，并测量了这种变异性如何影响系统发生树结构，从而影响遗传多样性。我们发现，对于强烈的异质性，扩展前沿的遗传构成在很大程度上取决于通过环境的最快路径集。然后，这些最优路径的景观依赖统计信息将取代种群内在噪声作为进化动力学的主要决定因素。值得注意的是，源自这些确定性路径的系统发生谱系合并的统计数据与均匀景观中仅由人口统计学噪声产生的统计数据非常相似。这告诫我们在解释合并统计数据时要谨慎，并为推断过去的种群动态带来了新的挑战。
