Data from: Interactions between host sex and age of exposure modify the virulence-transmission trade-off

The patterns of immunity conferred by host sex or age represent two sources of host heterogeneity that can potentially shape the evolutionary trajectory of disease. With each host sex or age encountered, a pathogen’s optimal exploitative strategy may change, leading to considerable variation in expression of pathogen transmission and virulence. To date, these host characteristics have been studied in the context of host fitness alone, overlooking the effects of host sex and age on the fundamental virulence-transmission trade-off faced by pathogens. Here we explicitly address the interaction of these characteristics and find that host sex and age at exposure to a pathogen affect age-specific patterns of mortality and the balance between pathogen transmission and virulence. When infecting age-structured male and female Daphnia magna with different genotypes of Pasteuria ramosa, we found that infection increased mortality rates across all age classes for females, whereas mortality only increased in the earliest age class for males. Female hosts allowed a variety of trade-offs between transmission and virulence to arise with each age and pathogen genotype. In contrast, this variation was dampened in males, with pathogens exhibiting declines in both virulence and transmission with increasing host age. Our results suggest that differences in exploitation potential of males and females to a pathogen can interact with host age to allow different virulence strategies to coexist, and illustrate the potential for these widespread sources of host heterogeneity to direct the evolution of disease in natural populations.宿主性别或年龄所赋予的免疫模式，是两类可潜在塑造疾病演化轨迹的宿主异质性来源。当病原体遭遇不同性别的宿主或不同年龄段的宿主时，其最优利用策略可能发生改变，进而导致病原体传播与毒力的表达出现显著差异。迄今为止，相关研究仅围绕宿主适合度对这类宿主特征展开探讨，却忽略了宿主性别与年龄对病原体所面临的基本毒力-传播权衡（virulence-transmission trade-off）的影响。本研究明确剖析了这些特征间的交互作用，发现宿主暴露于病原体时的性别与年龄，会影响特定年龄的死亡模式，以及病原体传播与毒力之间的平衡关系。我们采用不同基因型的拉姆氏巴斯德杆菌（Pasteuria ramosa）感染具有年龄结构的雌雄大型溞（Daphnia magna），结果显示：感染会提升所有年龄组雌性宿主的死亡率，而仅在雄性宿主的最早年龄组中出现死亡率升高的现象。雌性宿主中，不同年龄与病原体基因型的组合下，可产生多种传播与毒力之间的权衡模式。与之形成鲜明对比的是，雄性宿主中的这类变异受到抑制，病原体的毒力与传播能力均随宿主年龄增长而呈现下降趋势。研究结果表明，雌雄宿主对病原体的利用潜力差异，可与宿主年龄产生交互作用，使得不同毒力策略得以共存；同时也证实了这类广泛存在的宿主异质性来源，具备指导自然种群中疾病演化的潜在可能。