Department of Mathematics and Department of Biology, St. Olaf College, Northfield, Minnesota, 55057, USA.
Département de sciences biologiques, Université de Montréal, Montréal, Québec, Canada.
Ecology. 2021 Feb;102(2):e03229. doi: 10.1002/ecy.3229. Epub 2020 Dec 23.
Migration can allow individuals to escape parasite infection, which can lead to a lower infection probability (prevalence) in a population and/or fewer parasites per individual (intensity). Because individuals with more parasites often have lower survival and/or fecundity, infection intensity shapes the life-history trade-offs determining when migration is favored as a strategy to escape infection. Yet, most theory relies on susceptible-infected (SI) modeling frameworks, defining individuals as either healthy or infected, ignoring details of infection intensity. Here, we develop a novel modeling approach that captures infection intensity as a spectrum, and ask under what conditions migration evolves as function of how infection intensity changes over time. We show that relative timescales of migration and infection accumulation determine when migration is favored. We also find that population-level heterogeneity in infection intensity can lead to partial migration, where less-infected individuals migrate while more infected individuals remain resident. Our model is one of the first to consider how infection intensity can lead to migration. Our results frame migratory escape in light of infection intensity rather than prevalence, thus demonstrating that decreased infection intensity should be considered a benefit of migration, alongside other typical drivers of migration.
迁移可以使个体逃避寄生虫感染，这可能导致种群中较低的感染概率（流行率）和/或个体中较少的寄生虫（强度）。由于寄生虫较多的个体通常生存和/或繁殖能力较低，感染强度决定了何时将迁移作为逃避感染的策略，从而塑造了决定生活史权衡的轨迹。然而，大多数理论都依赖于易感-感染（SI）建模框架，将个体定义为健康或感染，忽略了感染强度的细节。在这里，我们开发了一种新的建模方法，将感染强度作为一个范围来捕获，并询问在什么条件下，迁移会随着感染强度随时间变化的方式而演变。我们表明，迁移和感染积累的相对时间尺度决定了何时迁移有利。我们还发现，感染强度的种群水平异质性可能导致部分迁移，即感染程度较低的个体迁移，而感染程度较高的个体则留在原地。我们的模型是第一个考虑感染强度如何导致迁移的模型之一。我们的结果从感染强度而不是流行率的角度来描述迁徙逃避，因此表明，与其他典型的迁徙驱动因素一起，应将感染强度的降低视为迁徙的一个好处。
