Data from: The relationship between parasite fitness and host condition in an insect - virus system

Research in host-parasite evolutionary ecology has demonstrated that environmental variation plays a large role in mediating the outcome of parasite infection. For example, crowding or low food availability can reduce host condition and make them more vulnerable to parasite infection. This observation that poor-condition hosts often suffer more from parasite infection compared to healthy hosts has led to the assumption that parasite productivity is higher in poor-condition hosts. However, the ubiquity of this negative relationship between host condition and parasite fitness is unknown. Moreover, examining the effect of environmental variation on parasite fitness has been largely overlooked in the host-parasite literature. Here we investigate the relationship between parasite fitness and host condition by using a laboratory experiment with the cabbage looper Trichoplusia ni and its viral pathogen, AcMNPV, and by surveying published host-parasite literature. Our experiments demonstrated that virus productivity was positively correlated with host food availability and the literature survey revealed both positive and negative relationships between host condition and parasite fitness. Together these data demonstrate that contrary to previous assumptions, parasite fitness can be positively or negatively correlated with host fitness. We discuss the significance of these findings for host-parasite population biology.宿主-寄生虫进化生态学（host-parasite evolutionary ecology）领域的已有研究证实，环境变异在调控寄生虫感染结局中扮演着核心角色。例如，种群拥挤或食物可获得性不足会降低宿主健康状态，使其更易遭受寄生虫感染。鉴于状态欠佳的宿主相较健康宿主往往会承受更严重的寄生虫感染危害，学界据此提出假设：状态欠佳的宿主体内寄生虫繁殖力更高。然而，这种宿主健康状态与寄生虫适合度之间的负相关关系是否具有普遍性，目前尚无定论。此外，在宿主-寄生虫相关研究领域中，环境变异对寄生虫适合度的影响长期以来被极大程度忽视。本研究通过针对粉纹夜蛾（Trichoplusia ni）及其病毒病原体苜蓿银纹夜蛾核型多角体病毒（AcMNPV）的室内实验，结合对已发表宿主-寄生虫研究文献的系统调研，探究了寄生虫适合度与宿主健康状态之间的关联。实验结果表明，病毒繁殖力与宿主食物可获得性呈正相关；而文献调研则揭示，宿主健康状态与寄生虫适合度之间同时存在正相关与负相关两种关联。综合上述研究结果可见，与此前的学术假设相悖，寄生虫适合度与宿主健康状态之间既可能呈正相关，也可能呈负相关。本文最后讨论了上述研究发现对宿主-寄生虫种群生物学领域的研究意义。