Repeated extinction and recolonization events generate a landscape of host populations that vary in their time since colonization. Within this dynamic landscape, pathogens that excel at invading recently colonized host populations are not necessarily those that perform best in host populations at or near their carrying capacity, potentially giving rise to divergent selection for pathogen traits that mediate the invasion process. Rarely, however, has this contention been empirically tested. Using Daphnia magna, we explored how differences in the colonization history of a host population influence the invasion success of different genotypes of the pathogen Pasteuria ramosa. By partitioning the pathogen invasion process into a series of individual steps, we show that each pathogen optimizes invasion differently when encountering host populations that vary in their time since colonization. All pathogen genotypes were more likely to establish successfully in recently colonized host populations, but the production of transmission spores was typically maximized in either the subsequent growth or stationary phase of host colonization. Integrating across the first three pathogen invasion steps (initial establishment, proliferation, and secondary infection) revealed that overall pathogen invasion success (and its variance) was, nonetheless, highest in recently colonized host populations. However, only pathogens that were slow to kill their host were able to maximize host‐facilitated dispersal. This suggests that only a subset of pathogen genotypes—the less virulent and more dispersive—are more likely to encounter newly colonized host populations at the front of a range expansion or in metapopulations with high extinction rates. Our results suggest a fundamental trade‐off for a pathogen between dispersal and virulence, and evidence for higher invasion success in younger host populations, a finding with clear implications for pathogen evolution in spatiotemporally dynamic settings.

中文翻译：

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斑块状种群中的感染：自宿主定殖以来不同时间的病原体入侵成功与扩散对比

重复的灭绝和再定殖事件产生了宿主种群的情况，这些种群自定殖以来的时间有所不同。在这种动态环境下，擅长入侵最近定居的寄主种群的病原体不一定是那些在其承载能力或接近其承载能力的寄主种群中表现最佳的病原体，可能导致对介导入侵过程的病原体性状的选择不同。然而，很少有经验证明这一观点。利用大型蚤（Daphnia magna），我们探讨了寄主种群的殖民历史中的差异如何影响不同基因型病原巴斯德氏菌的入侵成功。。通过将病原体入侵过程划分为一系列单独的步骤，我们显示，每种病原体在遇到定居以来时间不同的宿主种群时，优化入侵的方式也有所不同。所有病原体基因型更可能在最近定植的寄主种群中成功建立，但传播孢子的产生通常在随后的寄主定植生长或静止期达到最大。对前三个病原体入侵步骤（初始建立，增殖和继发感染）的整合显示，尽管如此，在最近定居的寄主种群中，总的病原体入侵成功率（及其变异）最高。但是，只有杀死宿主慢的病原体才能够最大程度地促进宿主的扩散。这表明，只有一部分病原体基因型（低毒力和高分散性）更有可能在范围扩展的前部或灭绝率高的种群中遇到新定居的寄主种群。我们的结果表明，病原体应在扩散和毒力之间进行权衡，并且有证据表明年轻寄主群体的入侵成功率更高，这一发现对时空动态环境中病原体的进化具有明显的意义。