Are blackcaps current winners in the evolutionary struggle against the common cuckoo?
Are blackcaps current winners in the evolutionary struggle against the common cuckoo?
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DOI：
10.1007/s10164-004-0119-1
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发表时间：
2004-01-01
影响因子：
0.9
通讯作者：
Mrlík, V
中科院分区：
文献类型：
--
作者：
Honza, M;Procházka, P;Mrlík, V
黑帽Sylvia atricapilla拒绝人工布谷鸟卵，它们的卵在同一窝内的外观变化很小，而在不同窝之间的卵变化很大。卵窝内的低变异有助于区分寄生卵，而卵窝之间的高变异则使杜鹃更难模仿某种寄主物种的卵。这些特征很可能是为了对抗普通布谷鸟（Cuculus canorus）的幼虫寄生而进化而来的，尽管今天黑头莺并不经常被寄生。在这项研究中，我们通过将三种类型的卵引入它们的巢中，研究了该物种对寄生卵的排斥是如何微调的：一种近似杜鹃卵大小的真正的非模拟卵，一种杜鹃卵大小的人工模拟卵和一种真正的同种卵。由于在以往的研究中，模拟和非模拟人工布谷鸟卵的排斥频率都很高，个体之间的排斥行为差异很低，表明种群中大多数个体都能够排斥寄生卵。因此，我们预测：(1)在所有个体中，卵外观的差异应该普遍较低；(2)对于同种卵，排斥决策应该高度依赖于寄生卵和宿主卵之间的模仿程度。我们发现了对这些预测的支持，这表明由于它们对幼虫寄生的高度复杂的对策，黑头莺可能被视为与普通杜鹃军备竞赛的当前赢家。此外，在欧洲各地发现的布谷鸟对布谷鸟卵的高且一致的排斥频率支持了空间栖息地结构假说，该假说认为，在树木附近繁殖的林地筑巢物种，如黑头莺，可能在过去的整个范围内都经历了高水平的寄生，因此，它们的排斥行为一旦进化，就会迅速传播到所有种群。
Blackcaps Sylvia atricapilla reject artificial cuckoo eggs, and their eggs vary little in appearance within clutches, whereas among clutches eggs vary considerably. Low variation within clutches facilitates discrimination of parasitic eggs, whereas high variation among clutches makes it harder for the cuckoo to mimic the eggs of a certain host species. These traits have most probably evolved as counteradaptations against brood parasitism by the common cuckoo Cuculus canorus, even though blackcaps are not regularly parasitised today. In this study, we investigated how fine-tuned the rejection of parasitic eggs is in this species by introducing three types of eggs into their nests: a real non-mimetic egg the approximate size of a cuckoo egg, an artificial mimetic egg the size of a cuckoo egg and a real conspecific egg. As the rejection frequency of both mimetic and non-mimetic artificial cuckoo eggs has been shown to be high in previous studies, the variation in rejection behaviour between individuals is low, indicating that most individuals within the population are able to reject parasitic eggs. Thus, we predict that (1) the intraclutch variation in egg appearance should be generally low in all individuals, and that (2) regarding conspecific eggs, rejection decisions should be highly dependent on the degree of mimicry between parasitic and host eggs. We found support for these predictions, which indicates that due to their highly sophisticated countermeasures against brood parasitism, blackcaps can probably be regarded as current winners of the arms race with the common cuckoo. Furthermore, the high and consistent rejection frequency of cuckoo eggs found throughout Europe for this species supports the spatial habitat structure hypothesis, which claims that woodland-nesting species breeding near trees, like blackcaps, presumably experienced a high level of parasitism throughout their range in the past and, therefore, their rejection behaviour, once evolved, spread rapidly to all populations.