Ministry of Education Key Laboratory for Biodiversity Sciences and Ecological Engineering, College of Life Sciences, Beijing Normal University, Beijing 100875, People's Republic of China.
Department of Behavioural Ecology and Evolutionary Genetics, Max Planck Institute for Ornithology, Seewiesen 82319, Germany.
Proc Biol Sci. 2023 Feb 22;290(1993):20222094. doi: 10.1098/rspb.2022.2094.
The arms race between brood parasites and their hosts provides a classic model to study coevolution. Hosts often reject the parasitic egg, and brood parasites should therefore select host nests in which the colour of the eggs best matches that of their own. Although this hypothesis has received some support, direct experimental evidence is still lacking. Here, we report on a study of Daurian redstarts, which show a distinct egg-colour dimorphism, with females laying either blue or pink eggs. Redstarts are often parasitized by common cuckoos, which lay light blue eggs. First, we showed that cuckoo eggs were more similar in spectral reflectance to the blue than to the pink redstart egg morph. Second, we report that the natural parasitism rate was higher in blue than in pink host clutches. Third, we performed a field experiment in which we presented a dummy clutch of each colour morph adjacent to active redstart nests. In this set-up, cuckoos almost always chose to parasitize a blue clutch. Our results demonstrate that cuckoos actively choose redstart nests in which the egg colour matches the colour of their own eggs. Our study thus provides direct experimental evidence in support of the egg matching hypothesis.
巢寄生鸟类与其宿主之间的军备竞赛为研究共同进化提供了一个经典模式。宿主通常会拒绝寄生鸟的卵，因此巢寄生鸟类应该选择那些卵的颜色与其自身卵的颜色最为匹配的宿主巢穴。尽管这一假说得到了一些支持，但仍缺乏直接的实验证据。在这里，我们报告了一项关于达乌里寒鸦的研究，达乌里寒鸦的卵呈现出明显的颜色二态性，雌性会产下蓝色或粉色的卵。寒鸦经常被普通杜鹃寄生，而普通杜鹃会产下淡蓝色的卵。首先，我们发现杜鹃卵在光谱反射率上与蓝色寒鸦卵更为相似，而与粉色寒鸦卵形态差异较大。其次，我们报告说，蓝色宿主巢中的自然寄生率高于粉色宿主巢中的自然寄生率。第三，我们进行了一项野外实验，在其中将每个颜色形态的假卵巢放置在活跃的寒鸦巢旁边。在这种设置下，杜鹃几乎总是选择寄生蓝色的卵巢。我们的研究结果表明，杜鹃会主动选择与自身卵颜色相匹配的寒鸦巢来进行寄生。因此，我们的研究提供了直接的实验证据，支持了卵匹配假说。
