Department of Biology, Aquatic Ecology Unit, Ecology Building, Lund University, Lund, Sweden.
Department of Environmental and Life Sciences, Karlstad University, Karlstad, Sweden.
J Anim Ecol. 2019 Oct;88(10):1510-1521. doi: 10.1111/1365-2656.13047. Epub 2019 Jul 8.
Numerous species adopt inducible defence strategies; that is, they have phenotypically plastic traits that decrease the risk of capture and consumption by potential predators. The benefits of expressing alternative phenotypes in high- vs. low-risk environments are well documented. However, inducible anti-predator traits are also expected to incur costs, as they are not expressed when predators are absent, yet empirical evidence of such costs remains scarce. Virtually, all animals in nature are simultaneously under strong selection to evade both capture by predators and infection by parasites or pathogens and, hence, display a diverse arsenal of defences to combat these threats, raising the possibility of trade-offs between defences. A classic example of a predator-induced morphological defence is the deep-bodied shape of crucian carp that reduces risk of predation from gape-size-limited predators. The goal of this study was to examine whether predator exposure affects also immune function in crucian carp, and whether the degree of expressed morphological defence is traded off against immune function in individuals. Following exposure to manipulations of perceived risk (predator presence/absence) in a long-term experiment (8 months), key aspects of innate immune function and individual differences in the expression of inducible morphological defence were quantified. Predator-exposed individuals showed lower haptoglobin levels and complement activity, but higher natural antibody titres than fish from predator-free conditions. When experimentally challenged with a mimicked bacterial infection (LPS injection), fish reared in the presence of a natural predator showed a weaker immune response. Moreover, among predator-exposed individuals, the magnitude of morphological defence expression correlated with both baseline immune function and the ability to mount an immune response. However, these relationships were not consistently supportive of a general trade-off among defences. Our results suggest that fish exposed to predators on average reduce investment in immune function, and, further, the observed relationships among defences in predator-exposed individuals can best be explained from individual fitness and pace-of-life perspectives.
许多物种采用诱导防御策略；也就是说，它们具有表型可塑性特征，可以降低被捕食者捕获和消耗的风险。在高风险和低风险环境中表达替代表型的好处已有充分记录。然而，诱导型抗捕食者特征也预计会带来成本，因为在没有捕食者时它们不会表达，而这种成本的经验证据仍然很少。实际上，自然界中的几乎所有动物都同时受到强烈的选择，以逃避捕食者的捕捉和寄生虫或病原体的感染，因此表现出多样化的防御手段来应对这些威胁，这增加了防御之间权衡的可能性。捕食者诱导的形态防御的一个经典例子是鲫鱼的深体形状，它降低了被口大小限制的捕食者捕食的风险。本研究的目的是检验捕食者暴露是否也会影响鲫鱼的免疫功能，以及个体表达的形态防御程度是否与免疫功能成反比。在一项长期实验（8 个月）中，通过对感知风险（捕食者存在/不存在）的操纵，研究人员量化了先天免疫功能的关键方面和诱导形态防御的个体差异。与来自无捕食者条件的鱼类相比，暴露于捕食者的个体的结合珠蛋白水平和补体活性较低，但天然抗体滴度较高。当用模拟的细菌感染（LPS 注射）进行实验性挑战时，在有自然捕食者存在的情况下饲养的鱼类表现出较弱的免疫反应。此外，在暴露于捕食者的个体中，形态防御表达的幅度与基线免疫功能和免疫反应能力相关。然而，这些关系并不一致地支持防御之间的一般权衡。我们的研究结果表明，暴露于捕食者的鱼类平均减少了对免疫功能的投资，此外，在暴露于捕食者的个体中观察到的防御之间的关系可以从个体适应性和生活方式的角度得到最好的解释。
