Cameron T C, Metcalfe D, Beckerman A P, Sait S M
Genetics, Ecology and Evolution Research Group, Institute of Integrative and Comparative Biology, University of Leeds, Leeds, UK.
Ecology. 2007 May;88(5):1225-31. doi: 10.1890/06-0661.
Many natural enemies do not immediately kill their host, and the lag this creates between attack and host death results in mixed populations of uninfected and infected hosts. Both competition and parasitism are known to be major structuring forces in ecological communities; however, surprisingly little is known about how the competitive nature of infected hosts could affect the survival and dynamics of remaining uninfected host populations. Using a laboratory system comprising the Indian meal moth, Plodia interpunctella, and a solitary koinobiont parasitoid, Venturia canescens, we address this question by conducting replicated competition experiments between the unparasitized and parasitized classes of host larvae. For varying proportions of parasitized host larvae and competitor densities, we consider the effects of competition within (intraclass) and between (interclass) unparasitized and parasitized larvae on the survival, development time, and size of adult moths and parasitoid wasps. The greatest effects were on survival: increased competitor densities reduced survival of both parasitized and unparasitized larvae. However, unparasitized larvae survival, but not parasitized larvae survival, was reduced by increasing interclass competition. To our knowledge, this is the first experimental demonstration of the competitive superiority of parasitized over unparasitized hosts for limiting resources. We discuss possible mechanisms for this phenomenon, why it may have evolved, and its possible influence on the stability of host-parasite dynamics.
许多天敌不会立即杀死它们的宿主，而这种攻击与宿主死亡之间的时间差导致了未感染和已感染宿主的混合种群。竞争和寄生都是生态群落中的主要结构力量；然而，令人惊讶的是，对于受感染宿主的竞争特性如何影响剩余未感染宿主种群的生存和动态，我们知之甚少。我们使用一个由印度谷螟（Plodia interpunctella）和一种独居的类寄生蜂（Venturia canescens）组成的实验室系统，通过对未寄生和已寄生的宿主幼虫进行重复的竞争实验来解决这个问题。对于不同比例的已寄生宿主幼虫和竞争者密度，我们考虑未寄生和已寄生幼虫内部（类内）以及之间（类间）的竞争对成年蛾和寄生蜂的生存、发育时间以及大小的影响。最大的影响体现在生存方面：竞争者密度增加会降低已寄生和未寄生幼虫的生存率。然而，类间竞争的增加会降低未寄生幼虫的生存率，但不会降低已寄生幼虫的生存率。据我们所知，这是首次通过实验证明在资源竞争方面已寄生宿主比未寄生宿主具有竞争优势。我们讨论了这种现象可能的机制、它可能进化的原因以及它对宿主 - 寄生虫动态稳定性的可能影响。
