Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
Evolution. 2022 Jun;76(6):1183-1194. doi: 10.1111/evo.14507. Epub 2022 May 7.
Traditional mechanistic trade-offs between transmission and virulence are the foundation of nearly all theory on parasite virulence evolution. For obligate-host killer parasites, evolution toward intermediate virulence depends on a trade-off between virulence (time to death) and transmission (the number of progeny released upon death). Although several ecological factors impact optimal virulence strategies constrained by trade-offs, these factors have been insufficient to explain the intermediate virulence levels observed in nature. The timing of seasonal activity, or phenology, is a factor that commonly influences ecological interactions but is difficult to incorporate into virulence evolution studies. We present a mathematical model of a seasonal obligate-killer parasite to study the impact of host phenology on virulence evolution. The model demonstrates that host phenology can select for intermediate parasite virulence even when a traditional mechanistic trade-off between transmission and virulence is omitted. The optimal virulence strategy is impacted by both the host activity period duration and the host emergence timing variation. Parasites with lower virulence strategies are favored in environments with longer host activity periods and when hosts emerge synchronously. The results demonstrate that host phenology can be sufficient to select for intermediate virulence strategies, providing an alternative driver of virulence evolution in some natural systems.
传统的传播和毒力之间的机械权衡是几乎所有寄生虫毒力进化理论的基础。对于专性宿主杀手寄生虫来说，向中等毒力进化取决于毒力（死亡时间）和传播（死亡时释放的后代数量）之间的权衡。尽管有几个生态因素影响受权衡限制的最佳毒力策略，但这些因素还不足以解释自然界中观察到的中等毒力水平。季节性活动或物候的时间是一个通常影响生态相互作用的因素，但很难将其纳入毒力进化研究中。我们提出了一个季节性专性杀手寄生虫的数学模型，以研究宿主物候对毒力进化的影响。该模型表明，即使忽略了传播和毒力之间的传统机械权衡，宿主物候也可以选择中间寄生虫毒力。最佳毒力策略既受宿主活动期持续时间的影响，也受宿主出现时间变化的影响。在宿主活动期较长和宿主同步出现的环境中，具有较低毒力策略的寄生虫更受青睐。研究结果表明，宿主物候足以选择中间毒力策略，为某些自然系统中的毒力进化提供了另一种驱动因素。
