Data from: Costs of resistance and infection by a generalist pathogen

Pathogen infection is typically costly to hosts, resulting in reduced fitness. However, pathogen exposure may also come at a cost even if the host does not become infected. These fitness reductions, referred to as “resistance costs”, are inducible physiological costs expressed as a result of a trade-off between resistance to a pathogen and aspects of host fitness (e.g., reproduction). Here, we examine resistance and infection costs of a generalist fungal pathogen (Metschnikowia bicuspidata) capable of infecting a number of host species. Costs were quantified as reductions in host lifespan, total reproduction, and mean clutch size as a function of pathogen exposure (resistance cost) or infection (infection cost). We provide empirical support for infection costs and modest support for resistance costs for five Daphnia host species. Specifically, only one host species examined incurred a significant cost of resistance. This species was the least susceptible to infection, suggesting the possibility that host susceptibility to infection is associated with the detectability and size of resistance cost. Host age at the time of pathogen exposure did not influence the magnitude of resistance or infection cost. Lastly, resistant hosts had fitness values intermediate between unexposed control hosts and infected hosts. Although not statistically significant, this could suggest that pathogen exposure does come at some marginal cost. Taken together, our findings suggest that infection is costly, resistance costs may simply be difficult to detect, and the magnitude of resistance cost may vary among host species as a result of host life history or susceptibility.

病原体感染通常会对宿主造成适合度（fitness）下降的代价。然而，即便宿主未被感染，病原体暴露本身也可能带来相应代价。这类被称为“抗性代价（resistance costs）”的适合度下降，是宿主在病原体抗性与宿主适合度相关性状（如繁殖）之间进行权衡时所诱发的生理性代价。本研究针对一种可感染多种宿主物种的广谱性真菌病原体——二孢梅奇酵母（Metschnikowia bicuspidata）的抗性代价与感染代价展开探究。研究以宿主寿命、总繁殖量和平均窝卵数的下降量作为量化指标，分别以病原体暴露（对应抗性代价）或感染（对应感染代价）作为自变量来计算代价。我们针对5种水蚤属（Daphnia）宿主的实验结果为感染代价提供了实证支持，同时为抗性代价提供了有限的支持证据。具体而言，仅在所检测的1种宿主中观察到了显著的抗性代价，该宿主对感染的易感性最低，这表明宿主的感染易感性可能与抗性代价的可检测性及强度相关。病原体暴露时的宿主年龄并未对抗性代价或感染代价的强度产生影响。此外，抗性宿主的适合度介于未暴露对照组宿主与被感染宿主之间。尽管这一结果未达到统计学显著性，但仍可表明病原体暴露确实存在一定的边际代价。综合来看，我们的研究结果表明：感染本身存在代价，而抗性代价可能只是难以被检测到；同时，抗性代价的强度可能因宿主的生活史特征或感染易感性的不同而存在物种间差异。