Abstract Although egg color polymorphism has evolved as an effective defensive adaptation to brood parasitism, spatial variations in egg color polymorphism remain poorly characterized. Here, we investigated egg polymorphism in 647 host species (68 families and 231 genera) parasitized by 41 species of Old Word cuckoos (1 family and 11 genera) across Asia, Europe, Africa, and Australia. The diversity of parasitic cuckoos differs among continents, reflecting the continent-specific intensities of parasitic selection pressure on hosts. Therefore, host egg polymorphism is expected to evolve more frequently on continents with higher cuckoo diversity. We identified egg polymorphism in 24.1% of all host species and 47.6% of all host families. The common cuckoo Cuculus canorus utilized 184 hosts (28.4% of all host species). Hosts of the common cuckoo and of Chrysococcyx species were more likely to have polymorphic eggs than hosts parasitized by other cuckoos. Both the number of host species and the host families targeted by the cuckoo species were positively correlated with the frequency of host egg polymorphism. Most host species and most hosts exhibiting egg color polymorphism were located in Asia and Africa. Host egg polymorphism was observed less frequently in Australia and Europe. Our results also suggested that egg polymorphism tends to occur more frequently in hosts that are utilized by several cuckoo species or by generalist cuckoo species. We suggest that selection pressure on hosts from a given continent increases proportionally to the number of cuckoo species, and that this selection pressure may, in turn, favor the evolution of host egg polymorphism.

中文翻译：

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四大洲杜鹃寄主卵多态性的空间变异

摘要 尽管鸡蛋颜色多态性已经进化为对巢寄生的有效防御适应，但鸡蛋颜色多态性的空间变化仍然缺乏表征。在这里，我们调查了亚洲、欧洲、非洲和澳大利亚的 41 种古杜鹃（1 科和 11 属）寄生的 647 种宿主物种（68 科和 231 属）的卵多态性。寄生杜鹃的多样性在各大洲之间有所不同，反映了寄主寄生选择压力的大陆特定强度。因此，寄主卵多态性有望在布谷鸟多样性较高的大陆上更频繁地进化。我们在所有寄主物种的 24.1% 和所有寄主科的 47.6% 中发现了卵多态性。普通杜鹃 Cuculus canorus 使用了 184 个宿主（占所有宿主物种的 28.4%）。与被其他杜鹃寄生的宿主相比，普通杜鹃和 Chrysococcyx 物种的宿主更有可能拥有多态性卵。杜鹃物种所针对的寄主物种数量和寄主科均与寄主卵多态性频率呈正相关。大多数宿主物种和大多数表现出卵颜色多态性的宿主位于亚洲和非洲。在澳大利亚和欧洲很少观察到寄主卵多态性。我们的结果还表明，卵多态性往往在被几种杜鹃物种或通才杜鹃物种利用的宿主中更频繁地发生。我们建议来自给定大陆的宿主的选择压力与杜鹃物种的数量成正比增加，并且这种选择压力可能反过来有利于宿主卵多态性的进化。