Data from: Superinfection and the coevolution of parasite virulence and host recovery

Parasite strategies of host exploitation may be affected by host defence strategies and multiple infections. In particular, within-host competition between multiple parasite strains has been shown to select for higher virulence. However, little is known on how multiple infections could affect the coevolution between host recovery and parasite virulence. Here, we extend a coevolutionary model introduced by van Baalen (1998) to account for superinfection. When the susceptibility to superinfection is low, we recover van Baalen's results and show that there are two potential evolutionary endpoints: one with avirulent parasites and poorly defended hosts, and another one with high virulence and high recovery. However, when the susceptibility to superinfection is above a threshold, the only possible evolutionary outcome is one with high virulence and high investment into defence. We also show that within-host competition may select for lower host recovery, as a consequence of selection for more virulent strains. We discuss how different parasite and host strategies (superinfection facilitation, competitive exclusion) as well as demographic and environmental parameters, such as host fecundity or various costs of defence, may affect the interplay between multiple infections and host-parasite coevolution. Our model shows the interplay between coevolutionary dynamics and multiple infections may be affected by crucial mechanistic or ecological details.寄生虫对宿主的利用策略可能会受到宿主防御策略与多重感染的共同影响。具体而言，已有研究表明，多种寄生虫菌株间的宿主体内竞争会驱动演化出更高的毒力。然而，目前学界对多重感染如何影响宿主恢复与寄生虫毒力之间的协同演化关系仍知之甚少。本研究拓展了van Baalen（1998）提出的协同演化模型，以纳入超感染（superinfection）情境。当宿主对超感染的易感性较低时，我们复现了van Baalen的原有研究结果，并发现存在两类潜在演化终点：一类对应无毒力寄生虫与防御能力较弱的宿主，另一类则对应高毒力寄生虫与高宿主恢复能力。但当宿主对超感染的易感性突破某一阈值时，唯一可能的演化结果即为高毒力寄生虫与高防御投入的宿主。此外，我们还发现，由于演化选择倾向于毒力更强的菌株，宿主体内竞争可能会导致宿主恢复能力出现演化降低的趋势。我们进一步讨论了不同的寄生虫与宿主策略（如超感染促进、竞争排斥）以及人口统计学与环境参数（如宿主繁殖力或防御的各类成本），将如何影响多重感染与宿主-寄生虫协同演化之间的相互作用。本模型表明，协同演化动力学与多重感染之间的相互作用，可能会受到关键机制或生态细节的显著调控。