Host defences against cuckoo parasitism in a changing world

在不断变化的世界中宿主对杜鹃寄生的防御

• 批准号: NE/M00807X/1
• 负责人: Nicholas Davies
• 金额: $ 43.8万
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2015
• 资助国家: 英国
• 起止时间: 2015 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FM00807X%2F1
• 关键词: Host; defences; against; cuckoo; parasitism

Charles Darwin likened the natural world to an "entangled bank" in which organisms evolve not only in response to changes in their physical environment but also to ever changing interactions with other organisms - competitors, predators and parasites. The recent decline in cuckoos provides an opportunity to test, by field experiments, how their hosts have adapted to the reduced threat of brood parasitism. The cuckoo is one of Nature's most notorious cheats: it lays its eggs in the nests of other species (one per host nest) and when the young cuckoo hatches it evicts the host's eggs and young. The hosts are then doomed to raise a young cuckoo instead of a brood of their own. This interaction has provoked an "evolutionary arms race": hosts have evolved defences against cuckoos (attacking adult cuckoos and ejecting cuckoo eggs), while cuckoos have evolved tricks to beat these defences (rapid laying to avoid host detection, and eggs that mimic host eggs in size and colour). Our recent work has shown that reed warbler hosts vary their defences in response to parasitism risk.Our first question is: How do reed warblers assess parasitism risk? When parasitism rates are high, reed warblers readily approach adult cuckoos and they are more likely to reject an egg if they see a cuckoo at their nest (a real one or a model cuckoo placed by experiment). Therefore defences are influenced by personal information of local cuckoo activity. However, at low rates of parasitism, reed warblers are more reluctant to approach cuckoos and a cuckoo at the nest is less likely to trigger egg rejection. This suggests that defences are also influenced by other cues. Our experiments have revealed that reed warblers widen their source of information about local cuckoo activity by eavesdropping on neighbours (social information). If they have witnessed neighbours mobbing a cuckoo, they are more likely to approach and mob a cuckoo back at their own nest. However, we do not know whether social information of parasitism risk stimulates egg rejection, either on its own or by priming responses to personal information.We will test how egg rejection by reed warblers (responses to model cuckoo eggs) is influenced by their assessment of parasitism risk (varied by presenting models of adult cuckoos). With controlled experiments, we will vary both personal information of local parasitism risk (a cuckoo at the focal pair's own nest) and social information (a cuckoo plus broadcast of reed warbler mobbing calls on a neighbour's territory). Our second question is: How rapidly are defences mobilised in unparasitised host populations? The recent decline in cuckoos (65% decline in the UK since the 1980's) has resulted in many small, isolated, unparasitised reed warbler populations, where defences (mobbing adult cuckoos and egg rejection) are absent. At twelve such populations of colour-ringed birds, we will present models of adult cuckoos or control, harmless intruders, and add model cuckoo eggs to nests, to test how mobbing and egg rejection defences might be reignited by personal and social information of local cuckoo activity. We will then monitor these populations to test how defences spread to newly-settling pairs.Our third question is: How might a naïve host species first acquire defences? Using the dunnock, Prunella modularis, a host that has no defences against cuckoos, we will test by experiment whether personal and social information of the adult cuckoo as a novel enemy can induce defences against adult cuckoos and stimulate responses to cuckoo eggs.We hope that this study will provide novel insights into how organisms acquire information about threats from enemies in a changing world, how rapidly defences are acquired, and how behavioural change (in this case recognition of a new enemy) might set the stage for evolutionary change by exposing organisms to new selection pressures.

查尔斯达尔文把自然界比作一个“纠缠的银行”，在这个银行里，生物体的进化不仅是为了应对物理环境的变化，而且也是为了应对与其他生物体--竞争者、捕食者和寄生虫--不断变化的相互作用。最近杜鹃数量的减少提供了一个机会，可以通过田间实验来测试它们的宿主如何适应育雏寄生威胁的减少。布谷鸟是自然界最臭名昭著的骗子之一：它在其他物种的巢中产卵（每个宿主巢一个），当小布谷鸟孵化时，它会驱逐宿主的蛋和幼崽。于是，主人注定要养一只小杜鹃，而不是自己的一窝。这种相互作用引发了一场“进化军备竞赛”：宿主进化出了对布谷鸟的防御（攻击成年布谷鸟并排出布谷鸟蛋），而布谷鸟则进化出了击败这些防御的技巧（快速产卵以避免宿主发现，以及在大小和颜色上模仿宿主蛋）。我们最近的研究表明，苇莺宿主对寄生风险的反应是不同的。我们的第一个问题是：苇莺如何评估寄生风险？当寄生率很高时，苇莺很容易接近成年杜鹃，如果它们看到杜鹃在它们的巢里（一只真实的杜鹃或一只通过实验放置的模型杜鹃），它们更有可能拒绝蛋。因此，防御受到当地杜鹃活动的个人信息的影响。然而，在低寄生率下，苇莺更不愿意接近布谷鸟，而巢中的布谷鸟不太可能引发卵排斥。这表明防御也受到其他线索的影响。我们的实验表明，苇莺通过偷听邻居（社会信息）来扩大它们关于当地杜鹃活动的信息来源。如果他们目睹了邻居围攻布谷鸟，他们更有可能接近布谷鸟，并将布谷鸟赶回自己的巢穴。然而，我们不知道是否寄生风险的社会信息刺激鸡蛋排斥，无论是在其本身或启动反应的个人信息。我们将测试如何卵排斥芦苇莺（响应模型杜鹃蛋）是由他们的寄生风险评估（不同的成年杜鹃模型）的影响。通过控制实验，我们将改变本地寄生风险的个人信息（焦点对自己的巢中的布谷鸟）和社会信息（布谷鸟加上邻居领土上的芦苇莺骚扰呼叫的广播）。我们的第二个问题是：在未被寄生的宿主群体中，防御的动员有多快？最近杜鹃数量的减少（自20世纪80年代以来，英国减少了65%）导致了许多小的，孤立的，未寄生的苇莺种群，其中缺乏防御（围攻成年杜鹃和卵排斥）。在12个这样的种群的彩色环鸟，我们将提出模型的成年杜鹃或控制，无害的入侵者，并添加模型杜鹃蛋巢，以测试如何围攻和鸡蛋排斥防御可能会重新点燃的个人和社会信息的本地杜鹃活动。然后，我们将监测这些种群，以测试防御是如何传播到新定居的对。我们的第三个问题是：一个幼稚的宿主物种最初是如何获得防御的？我们将利用杜诺克（Dunnock），Prunella modularis（一种对杜鹃没有防御能力的宿主），通过实验测试成年杜鹃作为新敌人的个人和社会信息是否可以诱导对成年杜鹃的防御并刺激对杜鹃卵的反应。我们希望这项研究能够提供新的见解，了解生物体如何在不断变化的世界中获取有关敌人威胁的信息，获得防御的速度有多快，以及行为变化（在这种情况下是对新敌人的识别）如何通过将生物体暴露于新的选择压力而为进化变化奠定基础。

项目成果

Cuckoo: Cheating by Nature

• DOI: 10.5860/choice.191309
• 发表时间: 2001
• 作者: N. Davies

The Evolution of Predator Resemblance in Avian Brood Parasites

• DOI: 10.3389/fevo.2021.725842
• 发表时间: 2021-11
• 作者: J. York

Games: conflict, competition, and cooperation

游戏：冲突、竞争、合作

• 发表时间: 2019
• 作者: Davies NB

Combining personal with social information facilitates host defences and explains why cuckoos should be secretive.

• DOI: 10.1038/srep19872
• 发表时间: 2016-01-22
• 期刊: Scientific reports
• 影响因子: 4.6
• 作者: Thorogood R;Davies NB
• 通讯作者: Davies NB

Imperfect imposters

不完美的冒名顶替者

• 发表时间: 2018
• 期刊: Wildlife sound
• 作者: York JE