Cuckoo host interactions: co-evolution and learning

布谷鸟宿主互动：共同进化和学习

• 批准号: NE/D001439/1
• 负责人: Nicholas Davies
• 金额: $ 19.63万
• 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: 2006
• 资助国家: 英国
• 起止时间: 2006 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FD001439%2F1
• 关键词: Cuckoo; host; interactions; co; evolution

In Nature, conflicts between species often involve evolutionary arms races, eg. improvements in strategies of attack by predators/parasites lead to improvements in defence by prey/hosts, leading to further predator/parasite improvements, and so on. Interactions between the cuckoo Cuculus canorus and its hosts provide a good subject for studying this process. The cuckoo is a famous cheat: it relies on other bird species (hosts) to raise its young. It lays just one egg per host nest. If the hosts accept this, eleven days later the cuckoo chick hatches first. Just a few hours old, it then ejects the host's eggs, balancing them on its back, one by one, and heaving them over the nest rim. Not surprisingly, hosts have evolved defences. One is to eject eggs unlike their own. In response, the cuckoo has evolved into genetically-distinct races, each specialising on one host species and laying eggs just like its host eggs, which the hosts are less likely to notice. Another is to attack adult cuckoos and increase the likelihood of rejecting eggs if they see a cuckoo on their nest (and so are more certain of parasitism). In response, the cuckoo has evolved rapid laying (c. 10 seconds) to decrease the chance it alerts the host. Although the arms race has led to genetic changes in cuckoos and hosts, individuals are also likely to improve their success through learning. The aim is to examine a case of learning on each side. (a) Learning by hosts: Hosts readily approach and attack adult cuckoos, in marked contrast to their wariness of dangerous enemies, such as sparrowhawks. How do hosts come to recognise the cuckoo as a nest enemy? Previous studies show that host populations isolated from cuckoos still reject eggs unlike their own, but have a much weaker response to cuckoo mounts on their nest and this does not stimulate increased egg rejection as it does in parasitised populations. These results suggest that unparasitised host populations may simply not recognise the adult cuckoo as an enemy because they haven't had the chance to learn this. We will do experiments with presentations of mounts of various enemies to colour-ringed, known-aged, reed warblers (a favourite cuckoo host) to test the following: what features of a potential nest enemy induce mobbing; whether mobbing calls attract neighbours; whether this experience leads naive birds to increase their mobbing and egg rejection when they encounter the same enemy on their own territory; whether hosts are predisposed to react aggressively to cuckoos, or whether they can be tricked into learning that a novel, but harmless, bird is a nest enemy; whether social learning can transmit enemy recognition along a chain of host territories. (b) Learning by cuckoos: We have discovered that not only have cuckoos evolved a 'well-matched egg' for their particular host species, but also a 'well-tuned' chick. Nestling cuckoos raised by reed warblers have different begging calls from those raised by dunnocks. Experiments show that young cuckoos change their tune appropriately when swapped between host nests, so they must somehow learn, through experience, how best to beg. We will study the begging calls from hatching to test whether cuckoos try out different calls and learn, by trial and error, which to use. We will also do experiments in which we broadcast various cuckoo begging calls to different host species to test whether the calls chosen by the cuckoos are the ones which are most effective in stimulating their particular hosts to feed them. This study of how both hosts and cuckoos fine-tune their responses by learning will help us to understand how rapidly enemies can adapt to environmental changes. In future, we hope to incorporate the effects of learning on the course of cuckoo-host co-evolution.

在自然界中，物种之间的冲突往往涉及进化的军备竞赛，例如。捕食者/寄生虫攻击策略的改进导致了被捕食者/宿主防御策略的改进，进而导致捕食者/寄生虫的进一步改进，等等。杜鹃Cuculus canorus与其宿主之间的相互作用为研究这一过程提供了一个很好的主题。杜鹃是一个著名的骗子：它依赖于其他鸟类（宿主）来抚养它的幼崽。它只在一个寄主巢里产一个蛋。如果宿主接受这个条件，11天后，布谷鸟的幼鸟会先孵化。刚出生几个小时，它就把寄主的蛋一个接一个地放在背上，然后把它们举过巢缘。毫不奇怪，宿主进化出了防御系统。一种是排出与自己不同的卵。作为回应，布谷鸟已经进化成遗传上不同的种族，每个种族都专门针对一个宿主物种，并像其宿主卵一样产卵，宿主不太可能注意到。另一种是攻击成年杜鹃，如果它们看到杜鹃在巢上，增加拒绝蛋的可能性（因此更确定寄生）。作为回应，杜鹃进化出了快速产卵（c。10秒），以减少它提醒主机的机会。尽管军备竞赛导致了杜鹃和宿主的基因变化，但个体也可能通过学习来提高自己的成功率。其目的是研究每一方的学习案例。(a)通过宿主学习：杜鹃很容易接近和攻击成年杜鹃，与它们对危险敌人的警惕形成鲜明对比，比如雀鹰。宿主是如何将布谷鸟视为巢敌的？以前的研究表明，从杜鹃中分离出来的宿主种群仍然拒绝与自己不同的蛋，但对杜鹃巢上的坐骑的反应要弱得多，这不会像寄生种群那样刺激增加对蛋的排斥。这些结果表明，未被寄生的宿主种群可能只是没有将成年杜鹃视为敌人，因为它们没有机会学习这一点。我们将做实验，向已知年龄的色环苇莺展示各种敌人的坐骑（一个最喜欢的杜鹃宿主）来测试以下内容：一个潜在的巢敌的什么特征会引起围攻;围攻的叫声是否会吸引邻居;这种经历是否会导致天真的鸟类在自己的领土上遇到同一个敌人时增加围攻和蛋的排斥;宿主是否倾向于对布谷鸟做出攻击性反应，或者它们是否能被欺骗，从而了解到一种新的、但无害的鸟是巢穴的敌人;社会学习是否能沿着宿主领地的链条沿着传递敌人的识别。(b)学习cuckoos：我们已经发现，杜鹃不仅进化出了与其特定宿主物种“匹配良好的蛋”，而且还进化出了“协调良好”的小鸡。由苇莺饲养的杜鹃雏鸟的乞求叫声与由杜诺克饲养的杜鹃不同。实验表明，小杜鹃在不同的宿主巢穴之间交换时会适当地改变它们的音调，所以它们必须通过经验以某种方式学习如何最好地乞讨。我们将研究从孵化开始的乞讨叫声，以测试杜鹃是否会尝试不同的叫声，并通过反复试验来学习使用哪种叫声。我们还将做一些实验，向不同的宿主物种广播各种杜鹃的乞求叫声，以测试杜鹃选择的叫声是否是最有效地刺激其特定宿主喂养它们的叫声。这项关于宿主和布谷鸟如何通过学习来微调反应的研究将有助于我们了解敌人适应环境变化的速度。在未来，我们希望将学习的影响纳入杜鹃宿主共同进化的过程中。