School of Biological Sciences, Monash University, Clayton, Vic., Australia.
J Evol Biol. 2014 May;27(5):876-88. doi: 10.1111/jeb.12364. Epub 2014 Apr 14.
Immune responses are highly dynamic. The magnitude and efficiency of an immune response to a pathogen can change markedly across individuals, and such changes may be influenced by variance in a range of intrinsic (e.g. age, genotype, sex) and external (e.g. abiotic stress, pathogen identity, strain) factors. Life history theory predicts that up-regulation of the immune system will come at a physiological cost, and studies have confirmed that increased investment in immunity can reduce reproductive output and survival. Furthermore, males and females often have divergent reproductive strategies, and this might drive the evolution of sex-specific life history trade-offs involving immunity, and sexual dimorphism in immune responses per se. Here, we employ an experiment design to elucidate dose-dependent and sex-specific responses to exposure to a nonpathogenic immune elicitor at two scales--the 'ultimate' life history and the underlying 'proximate' immune level in Drosophila melanogaster. We found dose-dependent effects of immune challenges on both male and female components of reproductive success, but not on survival, as well as a response in antimicrobial activity. These results indicate that even in the absence of the direct pathogenic effects that are associated with actual disease, individual life histories respond to a perceived immune challenge--but with the magnitude of this response being contingent on the initial dose of exposure. Furthermore, the results indicate that immune responses at the ultimate life history level may indeed reflect underlying processes that occur at the proximate level.
免疫反应是高度动态的。个体对病原体的免疫反应的强度和效率可能会有明显的差异，这种变化可能受到一系列内在（如年龄、基因型、性别）和外在（如非生物胁迫、病原体种类、菌株）因素的变化影响。生活史理论预测免疫系统的上调会带来生理上的代价，研究证实，增加对免疫系统的投资会降低生殖产出和存活率。此外，男性和女性通常具有不同的生殖策略，这可能会导致涉及免疫的性别特异性生活史权衡以及免疫反应本身的性别二态性的进化。在这里，我们采用实验设计来阐明在两个尺度上——“终极”生活史和黑腹果蝇的潜在“近因”免疫水平——暴露于非致病性免疫激发剂时的剂量依赖性和性别特异性反应。我们发现免疫挑战对雄性和雌性生殖成功的各个组成部分都有剂量依赖性的影响，但对生存没有影响，同时还对抗菌活性有反应。这些结果表明，即使在没有与实际疾病相关的直接致病作用的情况下，个体的生活史也会对感知到的免疫挑战做出反应——但这种反应的幅度取决于最初的暴露剂量。此外，结果表明，终极生活史水平的免疫反应确实可能反映了近因水平上发生的潜在过程。
