Abstract

Coevolutionary arms races between brood parasites and hosts provide tractable systems for understanding antagonistic coevolution in nature; however, little is known about the fate of frontline antiparasite defenses when the host “wins” the coevolutionary arms race. By recreating bygone species interactions, using artificial parasitism experiments, lingering defensive behaviors that evolved in the context of parasitism can be understood and may even be used to identify the unknown agent of parasitism past. Here we present the first study of this type by evaluating lingering “frontline” nest defenses that have evolved to prevent egg laying in a former brood parasite host. The Australian reed warbler Acrocephalus australis is currently not parasitized but is known to exhibit fine-tuned egg discrimination—a defensive behavior indicative of a past brood parasite–host arms race and common in closely related parasitized species. Here, using 3D-printed models of adult brood parasites, we examined whether the Australian reed warbler also exhibits frontline defenses to adult brood parasites, and whether we could use these defenses to identify the warbler’s “ghost of parasitism past.” Our findings provide evidence that the Australian reed warbler readily engages in frontline defenses that are considered adaptive specifically in the context of brood parasitism. However, individuals were unable to discriminate between adults of different brood parasite species at their nest. Overall, our results demonstrate that despite a relaxation in selection, defenses against brood parasitism can be maintained across multiple stages of the host’s nesting cycle, and further suggest that, in accordance with previous findings, that learning may be important for fine-tuning frontline defense.

中文翻译：

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过去寄生的幽灵：前宿主中挥之不去的前线抗寄生虫防御

摘要

育雏寄生虫和宿主之间的共同进化军备竞赛为理解自然界中的对抗性共同进化提供了易于处理的系统；然而，当宿主“赢得”共同进化军备竞赛时，前线抗寄生虫防御的命运知之甚少。通过重建过去的物种相互作用，使用人工寄生实验，可以理解在寄生环境中进化的挥之不去的防御行为，甚至可以用来识别过去寄生的未知因素。在这里，我们通过评估挥之不去的“前线”巢穴防御系统来介绍这种类型的第一项研究，这些防御系统已经进化到可以防止在前育雏寄生虫宿主中产卵。澳大利亚芦苇莺Acrocephalus australis目前没有被寄生，但已知表现出微调的卵辨别力 - 一种防御行为，表明过去的育雏寄生虫 - 宿主军备竞赛，并且在密切相关的寄生物种中很常见。在这里，我们使用 3D 打印的成年育雏寄生虫模型检查了澳大利亚芦苇莺是否也表现出对成年育雏寄生虫的前线防御，以及我们是否可以使用这些防御来识别莺的“寄生鬼过去”。我们的研究结果提供了证据，表明澳大利亚芦苇莺很容易参与前线防御，这些防御被认为是专门在育雏寄生环境下的适应性。然而，个体无法区分巢穴中不同寄生寄生虫种类的成虫。总体而言，我们的结果表明，尽管选择有所放松，