Miller M R, White A, Boots M
Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, England, UK.
J Theor Biol. 2005 Sep 21;236(2):198-207. doi: 10.1016/j.jtbi.2005.03.005. Epub 2005 Apr 18.
In response to parasitic infection, hosts may evolve defences that reduce the deleterious effects on survivorship. This may be interpreted as a form of resistance, as long as infected hosts are able to either recover or reproduce. Here we distinguish two important routes to this form of resistance. An infected host may either: (1) tolerate pathogen damage, or (2) control the pathogen by inhibiting its growth. A model is constructed to examine the evolutionary dynamics of tolerance and control to a free-living microparasite, where both forms of resistance are costly in terms of other life-history traits. We do not observe polymorphism of tolerant genotypes. In contrast, the evolution of control may lead to disruptive selection, and ultimately dimorphism of extreme strains. The optimal host genotype also varies with the type of resistance-individuals invest more in tolerance and pay a greater cost. The free-living framework used makes the distinction between tolerance and control explicit but the distinction applies equally to directly transmitted parasites. Due to the evolutionary differences exhibited, it is important to design experiments that distinguish between the two forms of resistance.
作为对寄生虫感染的反应，宿主可能会进化出防御机制，以减少对生存的有害影响。只要受感染的宿主能够恢复或繁殖，这就可以被解释为一种抗性形式。在这里，我们区分了实现这种抗性形式的两条重要途径。受感染的宿主可能会：（1）耐受病原体的损害，或者（2）通过抑制病原体的生长来控制它。构建了一个模型来研究对自由生活的微寄生虫的耐受性和控制能力的进化动态，在这个模型中，两种抗性形式在其他生活史特征方面都是有代价的。我们没有观察到耐受基因型的多态性。相比之下，控制能力的进化可能导致分裂选择，并最终导致极端菌株的二态性。最优宿主基因型也因抗性类型而异——个体在耐受性方面投入更多，付出的代价也更大。所采用的自由生活框架明确区分了耐受性和控制能力，但这种区分同样适用于直接传播的寄生虫。由于所表现出的进化差异，设计能够区分这两种抗性形式的实验很重要。
