Balancing selection and drift in a polymorphic salamander metapopulation

Understanding how genetic variation is maintained in a metapopulation is a longstanding problem in evolutionary biology. Historical resurveys of polymorphisms have offered efficient insights about evolutionary mechanisms, but are often conducted on single, large populations, neglecting the more comprehensive view afforded by considering all populations in a metapopulation. Here, we resurveyed a metapopulation of spotted salamanders (Ambystoma maculatum) to understand the evolutionary drivers of frequency variation in an egg mass colour polymorphism. We found that this metapopulation was demographically, phenotypically, and environmentally stable over the last three decades. However, further analysis revealed evidence for two modes of evolution in this metapopulation—genetic drift and balancing selection. Although we cannot identify the balancing mechanism from these data, our findings present a clear view of contemporary evolution in colour morph frequency and demonstrates the importance of metapopulation-scale studies for capturing a broad range of evolutionary dynamics.

解析集合种群（metapopulation）内遗传变异的维持机制，是进化生物学领域长期存在的经典科学问题。针对遗传多态性（polymorphism）的历史重监测研究，曾为解析进化机制提供了高效的研究视角，但这类研究多聚焦于单一大型种群，忽略了将集合种群内所有种群纳入研究范畴所能获得的更全面认知。本研究对斑点钝口螈（Ambystoma maculatum）的集合种群开展重监测，以解析卵块颜色多态性的频率变异的进化驱动因素。研究发现，在过去三十年中，该集合种群在种群统计学、表型与环境维度均保持稳定。不过进一步分析显示，该集合种群存在两种进化模式的相关证据——遗传漂变（genetic drift）与平衡选择（balancing selection）。尽管本研究无法通过现有数据确定具体的平衡选择机制，但研究结果清晰呈现了颜色形态频率的当代进化特征，并证实了集合种群尺度研究对于捕捉广泛进化动态的重要意义。