van Boven Michiel, Weissing Franz J
Animal Sciences Group, Wageningen University and Research Centre, PO Box 65, 8200 AB Lelystad, The Netherlands.
Am Nat. 2004 Feb;163(2):277-94. doi: 10.1086/381407. Epub 2004 Feb 13.
How much of its resources should an individual invest in a costly immune system? In this article, we apply an evolutionarily stable strategy analysis to an epidemic model to answer this question. On the one hand, an investment in immune function confers protection to infectious agents by reducing host susceptibility, pathogen virulence, or the length of the infectious period. On the other hand, an immune system is costly since it absorbs resources that otherwise might be invested in increasing the host's fertility or longevity. In addition, an active immune system may be able to clear pathogens efficiently but at the same time may result in immunopathology. By means of a reproductive value approach, we show how to compare the costs and benefits of an immune system systematically and how to derive the evolutionarily stable level of immune function. We then apply these methods to various plausible scenarios. The analysis reveals that the relationship between the life span of an organism and the optimal level of investment in immune function is less straightforward than one might expect. First, the prevalence of infection is reduced to the lowest possible level only under special circumstances. Second, members of a long-lived species do not necessarily have to invest more in immune function than those of a short-lived species. In fact, the opposite may be true. Third, the outcome of evolution can be contingent on the initial conditions. Depending on its initial investment strategy, a population may evolve to a state where very much or almost nothing is invested in a costly immune system.
个体应该将多少资源投入到一个成本高昂的免疫系统中呢？在本文中，我们将进化稳定策略分析应用于一个流行病模型来回答这个问题。一方面，对免疫功能的投入通过降低宿主易感性、病原体毒力或感染期的长度，为感染因子提供保护。另一方面，免疫系统成本高昂，因为它会消耗原本可用于提高宿主繁殖力或寿命的资源。此外，活跃的免疫系统可能能够有效地清除病原体，但同时也可能导致免疫病理。通过生殖价值方法，我们展示了如何系统地比较免疫系统的成本和收益，以及如何推导出进化稳定的免疫功能水平。然后，我们将这些方法应用于各种合理的情景。分析表明，生物体的寿命与免疫功能的最优投入水平之间的关系并不像人们预期的那么直接。首先，只有在特殊情况下，感染率才会降至尽可能低的水平。其次，长寿物种的成员不一定比短命物种的成员在免疫功能上投入更多。事实上，情况可能相反。第三，进化的结果可能取决于初始条件。根据其初始投资策略，一个种群可能进化到一种状态，在这种状态下，对成本高昂的免疫系统投入很多或几乎不投入。
