Data from: Environmental variation causes different (co) evolutionary routes to the same adaptive destination across parasite populations

Epidemics are engines for host-parasite coevolution, where parasite adaptation to hosts drives reciprocal adaptation in host populations. A key challenge is to understand whether parasite adaptation and any underlying evolution and coevolution is repeatable across ecologically realistic populations that experience different environmental conditions, or if each population follows a completely unique evolutionary path. We established twenty replicate pond populations comprising an identical suite of genotypes of crustacean host, Daphnia magna, and inoculum of their parasite, Pasteuria ramosa. Using a time-shift experiment, we compared parasite infection traits before and after epidemics and linked patterns of parasite evolution with shifts in host genotype frequencies. Parasite adaptation to the sympatric suite of host genotypes came at a cost of poorer performance on foreign genotypes across populations and environments. However, this consistent pattern of parasite adaptation was driven by different types of frequency-dependent selection that was contingent on an ecologically relevant environmental treatment (whether or not there was physical mixing of water within ponds). In unmixed ponds, large epidemics drove rapid and strong host-parasite coevolution. In mixed ponds, epidemics were smaller and host evolution was driven mainly by the mixing treatment itself; here, host evolution and parasite evolution were clear, but coevolution was absent. Population mixing breaks an otherwise robust coevolutionary cycle. These findings advance our understanding of the repeatability of (co)evolution across noisy, ecologically realistic populations.流行病是宿主-寄生虫协同进化的核心驱动力，寄生虫对宿主的适应性演化会推动宿主种群产生互惠适应。当前核心研究挑战在于明确：在经受不同环境扰动的生态现实种群中，寄生虫的适应性演化及其背后的进化与协同进化过程是否具备可重复性，抑或每个种群均会走向完全独特的进化轨迹。我们构建了20个重复池塘种群，所有种群的宿主均为基因型组成完全一致的甲壳动物大型溞（Daphnia magna），并接种了其专性寄生虫拉姆氏巴斯德杆菌（Pasteuria ramosa）的接种菌液。借助时移实验（time-shift experiment），我们对比了疫病流行前后的寄生虫感染性状，并将寄生虫演化模式与宿主基因型频率的变化进行了关联分析。寄生虫对同域宿主基因型组合的适应性演化，会伴随其在异域宿主基因型上感染能力的降低，这一适应性代价在所有种群与环境处理中均普遍存在。然而，这种一致性的寄生虫适应性演化模式，实则由不同类型的频率依赖选择所驱动，且该选择效应依赖于一项生态相关的环境处理——池塘水体是否发生物理混合。在未混合的池塘中，大规模疫病流行驱动了快速且强烈的宿主-寄生虫协同进化；而在混合池塘中，疫病流行规模更小，宿主演化主要由水体混合处理本身主导：尽管该环境下宿主与寄生虫的演化均清晰可辨，但协同进化并未发生。种群水体混合打破了原本稳定的协同进化循环。本研究结果深化了我们对生态现实且存在环境波动的种群中，（协同）进化可重复性的认知。