Kutzer Megan A M, Armitage Sophie A O
Institute for Evolution and Biodiversity, University of Münster, Hüfferstrasse 1, D-48149 Münster, Germany.
Institute for Evolution and Biodiversity, University of Münster, Hüfferstrasse 1, D-48149 Münster, Germany.
Zoology (Jena). 2016 Aug;119(4):281-9. doi: 10.1016/j.zool.2016.05.011. Epub 2016 May 27.
Tolerance, the ability of a host to limit the negative fitness effects of a given parasite load, is now recognised as an important host defence strategy in animals. Together with resistance, the ability of a host to limit parasite load, these two host strategies represent two disparate host responses to parasites, each with different predicted evolutionary consequences: resistance is predicted to reduce parasite prevalence, whereas tolerance could be neutral towards, or increase, parasite prevalence in a population. The distinction between these two strategies might have far-reaching epidemiological consequences. Classically, a reaction norm defines host tolerance because it depicts the change in host fitness as a function of parasite load, where a shallow negative slope indicates that host fitness slowly deteriorates as parasite load increases (i.e., high tolerance). Despite the fact that tolerance was only recently acknowledged to be an important component in an animal's immune repertoire, it is frequently referenced, so our aim is to emphasise the current advances on the topic. We begin by summarising the ways in which biologists measure the two components of tolerance, parasite load and fitness, as well as the ways in which the concept has been defined (i.e., point and range tolerance). It is common to test for variation in host tolerance according to intrinsic, innate factors, where variation exists among populations, genders or genotypes. Such variation in tolerance is pervasive across animal taxa, and we briefly review some of the mechanistic bases of variation that have recently begun to be explored. Three further novel advancements in the tolerance field are the appreciation of the role of extrinsic, environmental factors on tolerance, host tolerance in multi-host-parasite systems and individual-based approaches to tolerance measures. We explore these topics using recent examples and suggest some future perspectives. It is becoming increasingly clear that an appreciation of tolerance as a defence strategy can provide significant insights into how hosts coexist with parasites.
耐受性是宿主限制给定寄生虫负荷负面健康影响的能力，如今已被公认为动物体内一种重要的宿主防御策略。与抗性（宿主限制寄生虫负荷的能力）一起，这两种宿主策略代表了宿主对寄生虫的两种截然不同的反应，每种反应都有不同的预测进化后果：抗性预计会降低寄生虫的流行率，而耐受性可能对种群中的寄生虫流行率保持中性或使其增加。这两种策略之间的区别可能会产生深远的流行病学后果。传统上，反应规范定义了宿主耐受性，因为它描绘了宿主健康状况随寄生虫负荷的变化，其中浅负斜率表明随着寄生虫负荷增加，宿主健康状况缓慢恶化（即高耐受性）。尽管耐受性直到最近才被认为是动物免疫库中的一个重要组成部分，但它经常被提及，所以我们的目的是强调该主题的当前进展。我们首先总结生物学家测量耐受性的两个组成部分（寄生虫负荷和健康状况）的方法，以及该概念的定义方式（即点耐受性和范围耐受性）。根据内在的、先天的因素测试宿主耐受性的变化很常见，这些因素在种群、性别或基因型之间存在差异。这种耐受性的变化在动物类群中普遍存在，我们简要回顾一些最近开始探索的变化的机制基础。耐受性领域的另外三个新进展是认识到外在环境因素对耐受性的作用、多宿主 - 寄生虫系统中的宿主耐受性以及基于个体的耐受性测量方法。我们用最近的例子探讨这些主题，并提出一些未来的观点。越来越明显的是，将耐受性视为一种防御策略能够为宿主如何与寄生虫共存提供重要的见解。
