Data from: Coevolution is linked with phenotypic diversification but not speciation in avian brood parasites

Coevolution is often invoked as an engine of biological diversity. Avian brood parasites and their hosts provide one of the best-known examples of coevolution. Brood parasites lay their eggs in the nests of other species, selecting for host defences and reciprocal counter-adaptations in parasites. In theory, this arms race should promote increased rates of speciation and phenotypic evolution. Here we use recently developed methods to test whether the three largest avian brood parasitic lineages show changes in rates of phenotypic diversity and speciation relative to non-parasitic lineages. Our results challenge the accepted paradigm, and show that there is little consistent evidence that lineages of brood parasites have higher speciation or extinction rates than non-parasitic species. However, we provide the first evidence that the evolution of brood parasitic behaviour may affect rates of evolution in morphological traits associated with parasitism. Specifically, egg size and the colour and pattern of plumage have evolved up to nine times faster in parasitic than non-parasitic cuckoos. Moreover, cuckoo clades of parasitic species that are sympatric (and share similar host genera) exhibit higher rates of phenotypic evolution. This supports the idea that competition for hosts may be linked to the high phenotypic diversity found in parasitic cuckoos.协同演化（coevolution）常被视作生物多样性的核心驱动力。鸟类巢寄生者（brood parasite）及其宿主是协同演化最广为人知的案例之一。巢寄生鸟类将卵产于其他物种的巢中，这一过程会驱动宿主演化出防御策略，并反过来促使寄生鸟类演化出对应的反防御适应。从理论层面而言，这类演化军备竞赛应当会提升物种形成速率与表型演化速率。本研究采用新近开发的研究方法，对比寄生与非寄生鸟类支系，检验三大鸟类巢寄生支系的表型多样性与物种形成速率是否存在差异。本研究结果对现有主流范式提出了挑战：并无一致可靠的证据表明巢寄生鸟类支系的物种形成或灭绝速率高于非寄生鸟类。不过，本研究首次提供证据显示，巢寄生行为的演化可能会影响与寄生行为相关的形态性状的演化速率。具体而言，寄生杜鹃的卵大小、羽毛颜色与斑纹的演化速率最高可达非寄生杜鹃的九倍。此外，同域分布且宿主类群相似的寄生杜鹃支系，其表型演化速率更高。这一结果支持“宿主资源竞争或与寄生杜鹃的高表型多样性相关”这一假说。