Stokke Bard G, Moksnes Arne, Røskaft Eivin
Department of Zoology, Norwegian University of Science and Technology, Trondheim.
Evolution. 2002 Jan;56(1):199-205. doi: 10.1111/j.0014-3820.2002.tb00861.x.
Many passerine host species have counteracted the parasite egg mimicry in their coevolutionary arms race with the common cuckoo (Cuculus canorus) by evolving increased interclutch and reduced intraclutch variation in egg appearance. Such variations make it easier for hosts to recognize a foreign egg, reduce the possibility of making recognition errors, and reduce the ability of the cuckoo to mimic the eggs of a particular host. Here, we investigate if such clutch characteristics have evolved among North American passerines. We predict that due to the absence of brood parasites with egg mimicry on this continent, these passerines should (1) not show any relationship between rejection rates and intra- or interclutch variation, and (2) intraclutch variation should be lower and interclutch variation higher in European hosts exposed to cuckoo parasitism as compared to North American hosts parasitized by cowbirds. Here we present data that show support for most of these and other predictions, as well as when controlling statistically for effects of common descent. However, the effect of continent on intraclutch variation was less than predicted and we discuss a possible reason for this. All things considered, the results demonstrate that parasitism by a specialist brood parasite with egg mimicry is a powerful selective force regarding the evolution of egg characteristics in passerine birds.
在与杜鹃（大杜鹃）的协同进化军备竞赛中，许多雀形目寄主物种通过增加窝间差异和减少窝内卵外观差异，来对抗寄生虫卵拟态。这些差异使寄主更容易识别外来卵，降低识别错误的可能性，并降低杜鹃模仿特定寄主卵的能力。在此，我们研究了这些窝特征是否在北美雀形目鸟类中进化。我们预测，由于该大陆不存在具有卵拟态的巢寄生者，这些雀形目鸟类应该：（1）在拒绝率与窝内或窝间差异之间不表现出任何关系；（2）与被褐头牛鹂寄生的北美寄主相比，受到杜鹃寄生的欧洲寄主的窝内差异应该更低，窝间差异应该更高。在此，我们展示的数据支持了大多数这些预测和其他预测，以及在对共同祖先的影响进行统计控制时的情况。然而，大陆对窝内差异的影响小于预测，我们讨论了可能的原因。综合考虑，结果表明，具有卵拟态的专性巢寄生者的寄生是雀形目鸟类卵特征进化的强大选择力量。
