在受到寄生虫、病毒等病原体的攻击时，动物最常见的做法是通过免疫系统进行抵抗。不过，英国科学家对小鼠的一项最新研究表明，宿主抵御入侵还有另外一种选择，那就是妥协，逐渐进化为与入侵者共同生存。这一发现有望加深科学家对进化和传染病扩散的理解，并创造出更优良的家畜品种。相关论文发表在11月2日的《科学》杂志上。
植物有两种对付病原的策略：发展出强大的防御机制来进行抵抗，或者忍耐并尽量减少入侵者造成的伤害，比如它们会增加自身的光合作用，促进能量存储。很少有植物能够同时利用这两种方式。
为了弄清动物是否也会做出类似的选择，英国爱丁堡大学的生态学家Lars Råberg和同事让5种小鼠感染上能导致疟疾的寄生虫。随后，研究人员对这些小鼠的健康状况进行了监控，并测量了它们贫血和体重减轻的情况，这与血管中寄生虫的总量相关。
研究人员发现，与植物类似，这些小鼠也会采取强硬或者妥协两种方式。随着宿主体内寄生虫数量的加倍，一些小鼠种系会比另一些更加健康，这表明它们发展出了忍耐病原体的方法。此外，还有一些种系的小鼠能够保持寄生虫数量处于较低的水平，这说明它们能够主动地抵御感染。
不过，研究人员注意到，一种小鼠不会同时采取抵御策略与妥协策略，也就是无法“软硬兼施”。那些能够更顽强进行抵御的小鼠，对寄生虫的忍耐力却更差。与忍耐性强的小鼠相比，它们的体重会减轻更多，而且变得更加贫血。Råberg表示，这一现象或许说明，小鼠主导妥协策略和抵抗策略的深层遗传学机制是不同的。此外，新的发现还揭示出病原体进化的重要特征，即如果宿主选择妥协，它们就不会急于发展出更强的致命性。同时，妥协并不是一种十分理想的策略，因为如果机体不破坏杀灭这些病原体，它们就更有可能发生传播和扩散。
美国杜克大学的进化生物学家Mark Rausher表示，新的发现有望影响家畜培育策略，让鸡和猪具有更大的忍耐性或许能更好地抵御病原攻击。（科学网 任霄鹏/编译）
原始出处:
Science 2 November 2007:
Vol. 318. no. 5851, pp. 812 - 814
DOI: 10.1126/science.1148526
Disentangling Genetic Variation for Resistance and Tolerance to Infectious Diseases in Animals
Lars Råberg,1,2* Derek Sim,1 Andrew F. Read1
Hosts can in principle employ two different strategies to defend themselves against parasites: resistance and tolerance. Animals typically exhibit considerable genetic variation for resistance (the ability to limit parasite burden). However, little is known about whether animals can evolve tolerance (the ability to limit the damage caused by a given parasite burden). Using rodent malaria in laboratory mice as a model system and the statistical framework developed by plant-pathogen biologists, we demonstrated genetic variation for tolerance, as measured by the extent to which anemia and weight loss increased with increasing parasite burden. Moreover, resistance and tolerance were negatively genetically correlated. These results mean that animals, like plants, can evolve two conceptually different types of defense, a finding that has important implications for the understanding of the epidemiology and evolution of infectious diseases.
1 Institute of Evolutionary Biology and Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, UK.
2 Department of Animal Ecology, Lund University, Ecology Building, 223 62 Lund, Sweden.
Present address: Center for Infectious Disease Dynamics, Departments of Biology and Entomology, Pennsylvania State University, 208 Mueller Lab, University Park, PA 16802, USA.
* To whom correspondence should be addressed. E-mail: lars.raberg@zooekol.lu.se
