Data and Code for: Resistance is futile: Weaker selection for resistance by abundant parasites increases prevalence and depresses host density

We model host evolution of costly resistance to infection and its dependence on environmental factors, such as nutrients. We find that higher nutrients can increase infection prevalence AND select for lower resistance. In turn, the model predicts that lower resistance drives infection prevalence even higher while depressing host density. The attached code performs the model analysis, produces the published figures, and conducts statistical analysis on the data (described below). We conducted a mesocosm experiment with mixtures of zooplankton host (Daphnia dentifera) genotypes, algal resources (Ankistrodesmus falcatus), and fungal parasites (Metschnikowia bicuspidata). Mesocosm populations were supplied with low or high nutrients (5 or 50 ug/L phosphorus and 100 or 1000 ug/L nitrogen). We measured densities of hosts along with age class (juvenile or adult), sex, infections status, and egg number and chlorophyll densities; these data are a subset of data published previously Walsman et al. Functional Ecology (https://doi.org/10.1111/1365-2435.14030; data at https://doi.org/10.5061/dryad.mw6m905zg). For the first time, we also report genotype frequencies for the mixed genotype treatments. Importantly, we found that high nutrients increased infection prevalence as well as selecting for the host genotype less resistant to infection; the resulting host evolution increased infection prevalence further and depressed host density. These data and code may be reused with citation of the corresponding publication ("‘Resistance is futile’: Weaker selection for resistance by abundant parasites increases prevalence and depresses host density" in The American Naturalist).

本研究构建了宿主对感染的代价性抗性演化模型，并探讨其对营养水平等环境因子的依赖性。研究发现，更高的营养水平可提升感染流行率，并选择出抗性更低的宿主表型。反过来，该模型预测，更低的宿主抗性会进一步推高感染流行率，同时降低宿主种群密度。随附代码可完成模型分析、生成已发表的图表，并对下述数据开展统计分析。
本研究开展了中型实验生态系（mesocosm）实验，实验使用了枝角类宿主（*Daphnia dentifera*）的混合基因型、藻类资源（*Ankistrodesmus falcatus*）以及真菌寄生虫（*Metschnikowia bicuspidata*）。中型生态系种群分别施加低营养或高营养水平处理（磷浓度为5或50 μg/L，氮浓度为100或1000 μg/L）。本研究测量了宿主种群密度、年龄阶段（幼体或成体）、性别、感染状态、产卵量以及叶绿素密度；本数据集为Walsman等人此前发表于*Functional Ecology*的研究数据的子集（文献DOI：https://doi.org/10.1111/1365-2435.14030；原始数据DOI：https://doi.org/10.5061/dryad.mw6m905zg）。本研究首次报告了混合基因型处理组的基因型频率数据。值得注意的是，本研究发现高营养水平不仅提升了感染流行率，还选择出了抗性较弱的宿主基因型；由此引发的宿主演化进一步推高了感染流行率，并降低了宿主种群密度。本数据集与代码可在引用对应发表论文（刊载于*The American Naturalist*的《"Resistance is futile": Weaker selection for resistance by abundant parasites increases prevalence and depresses host density》）的前提下重复使用。