Centre for Immunity, Infection and Evolution, Institute of Evolutionary Biology, School of Biology, University of Edinburgh, Ashworth Laboratories King's Buildings, West Mains Rd, Edinburgh, EH9 3JT, U.K.
NERC Centre for Ecology & Hydrology, Bush Estate Penicuik, Midlothian, EH26 0QB, U.K.
Ecol Evol. 2014 Sep;4(17):3408-19. doi: 10.1002/ece3.1192. Epub 2014 Aug 18.
Parasites play key ecological and evolutionary roles through the costs they impose on their host. In wild populations, the effect of parasitism is likely to vary considerably with environmental conditions, which may affect the availability of resources to hosts for defense. However, the interaction between parasitism and prevailing conditions is rarely quantified. In addition to environmental variation acting on hosts, individuals are likely to vary in their response to parasitism, and the combined effect of both may increase heterogeneity in host responses. Offspring hierarchies, established by parents in response to uncertain rearing conditions, may be an important source of variation between individuals. Here, we use experimental antiparasite treatment across 5 years of variable conditions to test how annual population productivity (a proxy for environmental conditions) and parasitism interact to affect growth and survival of different brood members in juvenile European shags (Phalacrocorax aristotelis). In control broods, last-hatched chicks had more plastic growth rates, growing faster in more productive years. Older siblings grew at a similar rate in all years. Treatment removed the effect of environment on last-hatched chicks, such that all siblings in treated broods grew at a similar rate across environmental conditions. There were no differences in nematode burden between years or siblings, suggesting that variation in responses arose from intrinsic differences between chicks. Whole-brood growth rate was not affected by treatment, indicating that within-brood differences were driven by a change in resource allocation between siblings rather than a change in overall parental provisioning. We show that gastrointestinal parasites can be a key component of offspring's developmental environment. Our results also demonstrate the value of considering prevailing conditions for our understanding of parasite effects on host life-history traits. Establishing how environmental conditions shape responses to parasitism is important as environmental variability is predicted to increase.
寄生虫通过对宿主造成的成本在生态和进化中扮演着关键角色。在野外种群中，寄生虫的影响很可能随环境条件而有很大差异，这可能会影响宿主防御资源的可利用性。然而，寄生虫与流行条件之间的相互作用很少被量化。除了作用于宿主的环境变化外，个体对寄生虫的反应也可能存在差异，两者的综合影响可能会增加宿主反应的异质性。父母为应对不确定的饲养条件而建立的后代等级，可能是个体之间差异的一个重要来源。在这里，我们使用实验性驱虫治疗方法，在 5 年的不同条件下，测试年度种群生产力（环境条件的代表）和寄生虫如何相互作用，从而影响未成年欧洲鸬鹚（Phalacrocorax aristotelis）不同雏鸟的生长和存活。在对照组中，最后孵化的雏鸟生长速度更具可塑性，在生产力更高的年份生长更快。年长的兄弟姐妹在所有年份的生长速度相似。治疗去除了环境对最后孵化的雏鸟的影响，因此在处理后的雏鸟中，所有的兄弟姐妹在所有的环境条件下都以相似的速度生长。线虫负担在不同年份或兄弟姐妹之间没有差异，这表明反应的差异来自于雏鸟之间的内在差异。整个雏鸟的生长率不受处理的影响，这表明兄弟姐妹之间的差异是由资源在兄弟姐妹之间的分配变化而不是整体父母供给的变化所驱动的。我们表明，胃肠道寄生虫可能是后代发育环境的关键组成部分。我们的研究结果还表明，考虑流行条件对于理解寄生虫对宿主生活史特征的影响具有重要价值。确定环境条件如何影响对寄生虫的反应很重要，因为预计环境变异性会增加。
