School of Biological Sciences, Queen's University Belfast, Belfast, UK.
School of Life Sciences, University of Lincoln, Lincoln, UK.
J Anim Ecol. 2018 Mar;87(2):500-510. doi: 10.1111/1365-2656.12763. Epub 2017 Nov 1.
Tolerance and resistance are the two ways in which hosts can lessen the effects of infection. Tolerance aims to minimize the fitness effects resulting from incumbent pathogen populations, whereas resistance aims to reduce the pathogen population size within the host. While environmental impacts on resistance have been extensively, recorded their impacts on variation in tolerance are virtually unexplored. Here, we ask how the environment, namely the host diet, influences the capacity of an organism to tolerate and resist infection, using a model host-parasite system, the burying beetle, Nicrophorus vespilloides and the entomopathogenic bacteria, Photorhabdus luminescens. We first considered dose-responses and pathogen dynamics within the host, and compared our findings to responses known from other host species. We then investigated how investment in tolerance and resistance changed under different nutritional regimes. Beetles were maintained on one of five diets that varied in their ratio of protein to fat for 48 hr and then injected with P. luminescens. Survival was monitored and the phenoloxidase (PO) response and bacterial load at 24-hr postinfection were ascertained. The dose required to kill 50% of individuals in this species was several magnitudes higher than in other species and the bacteria were shown to display massive decreases in population size, in contrast to patterns of proliferation found in other host species. Diet strongly modified host survival after infection, with those on the high fat/low protein diet showing 30% survival at 8 days, vs. almost 0% survival on the low-fat/high-protein diet. However, this was independent of bacterial load or variation in PO, providing evidence for diet-mediated tolerance mechanisms rather than immune-driven resistance. Evolutionary ecology has long focussed on immune resistance when investigating how organisms avoid succumbing to infection. Tolerance of infection has recently become a much more prominent concept and is suggested to be influential in disease dynamics. This is one of the first studies to find diet-mediated tolerance.
耐受和抗性是宿主减轻感染影响的两种方式。耐受旨在将由现有病原体种群引起的适应度效应最小化，而抗性则旨在降低宿主内的病原体种群大小。虽然环境对抗性的影响已经被广泛记录，但它们对耐受变异的影响实际上尚未得到探索。在这里，我们研究了环境（即宿主饮食）如何影响生物体耐受和抵抗感染的能力，使用了一种模型宿主-寄生虫系统，即埋葬甲，Nicrophorus vespilloides 和昆虫病原细菌，Photorhabdus luminescens。我们首先考虑了宿主内的剂量反应和病原体动态，并将我们的发现与其他宿主物种的反应进行了比较。然后，我们研究了在不同营养水平下耐受和抗性的投资如何变化。甲虫在五种不同的饮食中维持 48 小时，这些饮食的蛋白质与脂肪比例不同，然后用 P. luminescens 注射。监测存活率，并确定感染后 24 小时的酚氧化酶（PO）反应和细菌负荷。该物种杀死 50%个体所需的剂量比其他物种高几个数量级，并且细菌显示出种群数量的大幅减少，与在其他宿主物种中发现的增殖模式形成对比。饮食强烈改变了宿主感染后的存活率，高脂肪/低蛋白饮食的个体在 8 天时显示出 30%的存活率，而低脂肪/高蛋白饮食的个体几乎没有存活率。然而，这与细菌负荷或 PO 的变化无关，这为饮食介导的耐受机制而不是免疫驱动的抗性提供了证据。进化生态学在研究生物体如何避免感染时长期以来一直关注免疫抗性。感染耐受最近成为一个更为突出的概念，并被认为对疾病动态有影响。这是第一个发现饮食介导耐受的研究之一。
