BioGéoSciences, CNRS UMR 5561, Université de Bourgogne, Dijon 21000, France.
Int J Parasitol. 2013 Sep;43(10):861-7. doi: 10.1016/j.ijpara.2013.05.008. Epub 2013 Jun 20.
There is an increasing understanding of the context-dependent nature of parasite virulence. Variation in parasite virulence can occur when infected individuals compete with conspecifics that vary in infection status; virulence may be higher when competing with uninfected competitors. In vertebrates with social hierarchies, we propose that these competition-mediated costs of infection may also vary with social status. Dominant individuals have greater competitive ability than competing subordinates, and consequently may pay a lower prevalence-mediated cost of infection. In this study we investigated whether costs of malarial infection were affected by the occurrence of the parasite in competitors and social status in domestic canaries (Serinus canaria). We predicted that infected subordinates competing with non-infected dominants would pay higher costs than infected subordinates competing with infected dominants. We also predicted that these occurrence-mediated costs of infection would be ameliorated in infected dominant birds. We found that social status and the occurrence of parasites in competitors significantly interacted to change haematocrit in infected birds. Namely, subordinate and dominant infected birds differed in haematocrit depending on the infection status of their competitors. However, in contrast to our prediction, dominants fared better with infected subordinates, whereas subordinates fared better with uninfected dominants. Moreover, we found additional effects of parasite occurrence on mortality in canaries. Ultimately, we provide evidence for costs of parasitism mediated by social rank and the occurrence of parasites in competitors in a vertebrate species. This has important implications for our understanding of the evolutionary processes that shape parasite virulence and group living.
人们越来越了解寄生虫毒力的上下文依赖性。当感染个体与感染状态不同的同种个体竞争时，寄生虫毒力可能会发生变化；当与未感染的竞争者竞争时，毒力可能更高。在具有社会等级制度的脊椎动物中，我们提出，这些感染介导的竞争成本也可能随社会地位而变化。优势个体比竞争的下属具有更大的竞争能力，因此可能支付的感染流行介导的成本较低。在这项研究中，我们调查了疟疾感染的成本是否受到寄生虫在竞争者中的存在和家雀（Serinus canaria）中的社会地位的影响。我们预测，与非感染的优势个体竞争的感染下属会比与感染的优势个体竞争的感染下属支付更高的成本。我们还预测，这些感染发生介导的成本在感染的优势鸟类中会减轻。我们发现，社会地位和竞争者中寄生虫的存在显著相互作用，改变了感染鸟类的红细胞压积。即，下属和优势感染鸟类的红细胞压积取决于其竞争者的感染状态。然而，与我们的预测相反，优势鸟类在与感染的下属竞争时表现更好，而下属在与未感染的优势鸟类竞争时表现更好。此外，我们还发现寄生虫发生对金丝雀死亡率的额外影响。最终，我们为在脊椎动物物种中由社会等级和竞争者中寄生虫的存在介导的寄生虫寄生成本提供了证据。这对我们理解塑造寄生虫毒力和群体生活的进化过程具有重要意义。
