School of Mathematics and Statistics, University of Sheffield, Sheffield, UK.
J Evol Biol. 2021 Dec;34(12):1932-1943. doi: 10.1111/jeb.13947. Epub 2021 Oct 28.
Tolerance and resistance are two modes of defence mechanisms used by hosts when faced with parasites. Here, we assume tolerance reduces infection-induced mortality rate and resistance reduces the susceptibility of getting infected. Importantly, a negative association between these two strategies has often been found experimentally. We study the simultaneous evolution of resistance and tolerance in a host population where they are related by such a trade-off. Using evolutionary invasion theory, we examine the patterns of optimal investment in each defence strategy, under different ecological scenarios. Our focus is on predicting which of the two strategies is favoured under various epidemiological and ecological conditions. Our key findings surround the impact of recovery and sterility of infected hosts. As the rate at which infected hosts recover from the infection, that is the recovery rate increases, the investment in tolerance increases (resistance decreases) when infected hosts are sterile, but this pattern reverses when infected hosts can reproduce. We further found that a change in the parameter determining the intraspecies competition for resources leading to a reduction in birth rate, that is the crowding factor affects investments in tolerance and resistance only when infected hosts can reproduce. These results emphasize the role of fecundity in driving the evolutionary dynamics of a host. We also find that disease prevalence can increase or decrease depending on whether or not the host evolves: prevalence is highest at low recovery rates when the host does not evolve, but the feedback of a change in tolerance and resistance reverses this pattern, leading to lower prevalence at low recovery rates as host evolves.
耐受性和抵抗力是宿主在面对寄生虫时使用的两种防御机制模式。在这里，我们假设耐受性降低感染引起的死亡率，抵抗力降低感染的易感性。重要的是，这两种策略之间的负相关关系在实验中经常被发现。我们研究了在宿主种群中同时进化的抗性和耐受性，它们之间存在这种权衡关系。使用进化入侵理论，我们在不同的生态场景下研究了每种防御策略的最佳投资模式。我们的重点是预测在各种流行病学和生态条件下哪种策略更有利。我们的主要发现围绕着受感染宿主的恢复和不育性的影响。随着感染宿主从感染中恢复的速度，即恢复率增加，当感染宿主不育时，对耐受性的投资增加（抵抗力降低），但当感染宿主可以繁殖时，这种模式会逆转。我们还发现，决定种内资源竞争导致出生率降低的参数（拥挤因子）的变化仅在感染宿主可以繁殖时才会影响耐受性和抵抗力的投资。这些结果强调了生殖力在驱动宿主进化动态中的作用。我们还发现，疾病流行率可能会增加或减少，具体取决于宿主是否进化：当宿主不进化时，在低恢复率下流行率最高，但随着耐受性和抵抗力的变化反馈，这种模式会逆转，导致宿主进化时低恢复率下的流行率降低。
