Data from: Evolution of virulence in heterogeneous host communities under multiple trade-offs

Many pathogens and parasites are transmitted through hosts that differ in species, sex, genotype, or immune status. In addition, virulence (here defined as disease-induced mortality) and transmission can vary during the infectious period within hosts of different state. Most models of virulence evolution assume that transmission and virulence are constant over the infectious period and that the host population is homogenous. Here, we examine a multi-species SIR model where transmission occurs within and between species, and transmission and virulence varied during the infectious period. This allows us to understand virulence evolution in a broader range of situations that characterize many emerging diseases. Because emerging pathogens are by definition new to their host populations, they should be expected to rapidly adapt after emergence. We illustrate these evolutionary effects using the framework of adaptive dynamics to examine how virulence evolves after emergence in response to the relative strength of selection on pathogen fitness and mutational variance for virulence. We illustrate the role of evolution by simulating adaptive walks to an evolutionarily stable virulence. We found that the magnitude of between-species transmission and the relative timing of transmission and mortality across species were of primary importance for determining the evolutionarily stable virulence.诸多病原体与寄生虫可通过物种、性别、基因型或免疫状态存在差异的宿主进行传播。此外，毒力（本文将其定义为疾病引发的致死率）与传播能力在不同状态宿主的感染期内可发生动态变化。现有多数毒力进化模型均假设，感染期内的传播能力与毒力保持恒定，且宿主种群为同质种群。本文基于多物种SIR模型展开研究，该模型中传播可发生于物种内部与物种之间，且传播能力与毒力在感染期内存在动态变化。这使得我们能够在更广泛的场景下解析毒力进化规律，而这些场景正是诸多新发传染病的典型特征。根据定义，新发病原体对于其宿主种群而言是全新的病原，因此在出现后应会快速发生适应性演化。我们借助适应性动力学（adaptive dynamics）框架阐释此类演化效应，以此探究新发病原出现后，毒力如何响应病原体适合度选择的相对强度以及毒力相关的突变方差而发生演化。我们通过模拟向进化稳定毒力（evolutionarily stable virulence）的适应性行走过程，阐释演化的作用机制。研究发现，种间传播的强度以及不同物种间传播与死亡的相对时序，是决定进化稳定毒力的核心影响因素。