Donnelly R, White A, Boots M
Department of Mathematics, Heriot-Watt University, Edinburgh, UK.
Biosciences, College of Life and Environmental Sciences, University of Exeter, Exeter, UK.
J Evol Biol. 2017 Mar;30(3):561-570. doi: 10.1111/jeb.13025. Epub 2017 Jan 21.
Hosts are typically challenged by multiple parasites, but to date theory on the evolution of resistance has mainly focused on single infections. We develop a series of models that examine the impact of multiple parasites on the evolution of resistance under the assumption that parasites coexist at the host population scale as a consequence of superinfection. In this way, we are able to explicitly examine the impact of ecological dynamics on the evolutionary outcome. We use our models to address a key question of how host lifespan affects investment in resistance to multiple parasites. We show that investment in costly resistance depends on the specificity of the immune response and on whether or not the focal parasite leads to more acute infection than the co-circulating parasite. A key finding is that investment in resistance always increases as the immune response becomes more general independently of whether it is the focal or the co-circulating parasite that exploits the host most aggressively. Long-lived hosts always invest more than short-lived hosts in both general resistance and resistance that is specific to relatively acute focal parasites. However, for specific resistance to parasites that are less acute than co-circulating parasites it is the short-lived hosts that are predicted to invest most. We show that these results apply whatever the mode of defence, that is whether it is through avoidance or through increased recovery, with or without acquired immunity, or through acquired immunity itself. As a whole, our results emphasize the importance of considering multiple parasites in determining optimal immune investment in eco-evolutionary systems.
宿主通常会受到多种寄生虫的挑战，但迄今为止，抗性进化理论主要集中在单一感染上。我们开发了一系列模型，在假设由于重复感染寄生虫在宿主种群规模上共存的情况下，研究多种寄生虫对抗性进化的影响。通过这种方式，我们能够明确考察生态动态对进化结果的影响。我们用我们的模型来解决一个关键问题，即宿主寿命如何影响对多种寄生虫抗性的投入。我们表明，对代价高昂的抗性的投入取决于免疫反应的特异性，以及目标寄生虫是否比同时传播的寄生虫导致更急性的感染。一个关键发现是，无论最积极利用宿主的是目标寄生虫还是同时传播的寄生虫，随着免疫反应变得更具普遍性，对抗性的投入总是会增加。长寿宿主在一般抗性和对相对急性目标寄生虫的特异性抗性方面总是比短寿宿主投入更多。然而，对于对不如同时传播的寄生虫急性的寄生虫的特异性抗性，预计短寿宿主投入最多。我们表明，无论防御方式如何，即无论是通过回避还是通过提高恢复能力，有无获得性免疫，或者通过获得性免疫本身，这些结果都适用。总体而言，我们的结果强调了在生态进化系统中确定最佳免疫投入时考虑多种寄生虫的重要性。
