Bonhoeffer S, Lenski R E, Ebert D
Wellcome Centre for the Epidemiology of Infectious Disease, Department of Zoology, Oxford University, UK.
Proc Biol Sci. 1996 Jun 22;263(1371):715-21. doi: 10.1098/rspb.1996.0107.
We used a mathematical model to evaluate the hypothesis that parasites and pathogens with long living propagules should evolve high levels of virulence, i.e. high rates of pathogen-induced host mortality. Our model shows that the optimal level of virulence is independent of the longevity of the propagules either: (i) if the density or the prevalence of infected hosts is in (or fluctuates around) equilibrium; or (ii) if the death rate of the infected host population is high compared with that of the propagules. The level of virulence that maximizes the parasite's fitness (Multhusian parameter) increases with increasing longevity of its propagules only if the host-parasite system has not reached equilibrium and the death rate of the propagules is high relative to that of the infected hosts. Therefore, for parasites that have recently invaded a susceptible host population, greater propagule longevity may initially favour higher virulence; but once the equilibrium is reached the optimal virulence is independent of propagule longevity.
具有长寿传播体的寄生虫和病原体应该进化出高毒力水平，即由病原体引起的宿主高死亡率。我们的模型表明，毒力的最佳水平也与传播体的寿命无关：（i）如果受感染宿主的密度或患病率处于平衡状态（或围绕平衡波动）；或者（ii）如果受感染宿主种群的死亡率高于传播体的死亡率。只有当宿主 - 寄生虫系统尚未达到平衡且传播体的死亡率相对于受感染宿主的死亡率较高时，使寄生虫适应性（马尔萨斯参数）最大化的毒力水平才会随着其传播体寿命的增加而增加。因此，对于最近侵入易感宿主种群的寄生虫来说，传播体寿命更长最初可能有利于更高的毒力；但一旦达到平衡，最佳毒力就与传播体寿命无关了。
