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 colou...协同进化（coevolution）常被视为驱动生物多样性产生的核心动力。鸟类巢寄生者（avian brood parasites）与其宿主，便是协同进化最广为人知的研究案例之一。巢寄生者会将卵产于其他物种的巢穴中，这会对宿主的防御性状产生定向选择压力，进而推动宿主演化出防御策略，并反过来促使寄生者演化出对应的对抗适应机制。从理论层面而言，这类演化军备竞赛应当会提升物种形成与表型演化的速率。本研究采用新近开发的研究方法，针对三大鸟类巢寄生演化支，检验其相较于非寄生演化支，是否在表型多样性与物种形成速率上存在差异。本研究结果对这一公认的学术范式提出了挑战：并未发现一致的证据表明巢寄生演化支的物种形成或灭绝速率高于非寄生物种。不过，本研究首次提供证据表明，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，卵的大小与颜色……