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）领域的研究已证实，环境变异（environmental variation）在调控寄生虫感染结局中发挥着关键作用。例如，种群拥挤或食物可获得性不足会降低宿主健康状态（host condition），使其更易遭受寄生虫感染。鉴于健康状况较差的宿主往往比健康宿主承受更严重的寄生虫感染，学界此前曾提出假设：宿主健康状态越差，寄生虫的增殖能力（parasite productivity）越强。然而，宿主健康状态与寄生虫适合度（parasite fitness）之间的这种负相关关系是否具有普遍性，目前仍不明确。此外，探究环境变异对寄生虫适合度的影响这一议题，在宿主-寄生虫相关研究中长期被大幅忽视。本研究以粉纹夜蛾（Trichoplusia ni）及其病毒病原体苜蓿丫纹夜蛾核型多角体病毒（AcMNPV）为研究对象，通过室内控制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。实验结果显示，病毒增殖水平与宿主食物供给量呈正相关；而文献调研则表明，宿主健康状态与寄生虫适合度之间既存在正相关关系，也存在负相关关系。综合上述实验与调研数据可知，与此前的假设相悖，寄生虫适合度与宿主适合度（host fitness）之间的相关性可正可负。最后，本文讨论了上述发现对宿主-寄生虫种群生物学研究的重要意义。