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（parasite strategies of host exploitation）可能会受到宿主防御策略（host defence strategies）与多重感染（multiple infections）的影响。具体而言，已有研究证实，多种寄生虫菌株间的宿主体内竞争（within-host competition）会经进化选择促进更高毒力（virulence）菌株的演化。然而，目前学界对多重感染如何影响宿主恢复能力（host recovery）与寄生虫毒力之间的协同进化（coevolution）仍知之甚少。
本研究拓展了van Baalen（1998）提出的协同进化模型（coevolutionary model），以纳入超感染（superinfection）场景。当宿主对超感染的易感性（susceptibility to superinfection）较低时，我们复现了van Baalen的研究结果，并表明存在两种潜在的进化终点（evolutionary endpoints）：一种对应无毒力寄生虫（avirulent parasites）与防御能力较弱的宿主，另一种对应高毒力寄生虫与高宿主恢复能力的组合。然而，当宿主对超感染的易感性超过某一阈值时，唯一可能的进化结果（evolutionary outcome）为高毒力寄生虫与高防御投入的宿主。
我们还发现，宿主体内竞争可能会促使宿主恢复能力降低，这是选择更具毒力的寄生虫菌株所带来的演化结果。此外，我们讨论了不同的寄生虫与宿主策略（如超感染促进、竞争排除（competitive exclusion）），以及宿主繁殖力（host fecundity）、防御的各类成本等人口统计学与环境参数（demographic and environmental parameters），将如何影响多重感染与宿主-寄生虫协同进化之间的相互作用。
本模型表明，协同进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调控。