Data from: True recognition of nestlings by hosts selects for mimetic cuckoo chicks

Cuckoos lay their eggs in other birds’ nests, whereafter the young cuckoo hatches, ejects its nestmates, and monopolizes the care of the host parents. Theory predicts that hosts should not evolve to recognize and reject cuckoo chicks because of the risk of mistakenly imprinting on a cuckoo chick in their first brood and thereafter always rejecting their own chicks. However, recent studies have revealed some hosts do reject cuckoo chicks from the nest, indicating that these hosts’ recognition systems either do not rely on first brood imprinting, or use cues that are independent of chick phenotype. Here, we investigate the proximate mechanisms of chick rejection behaviour in the large-billed gerygone (Gerygone magnirostris), a host of the little bronze-cuckoo (Chalcites minutillus). We find that gerygones use true template-based recognition based on at least one visual chick trait (the amount of hatchling down-feathers), and that this is further mediated by experience of adult cuckoos at the nest during egg-laying. Given the theoretical constraints of acquiring recognition templates via imprinting, gerygones must possess a template of own-chick appearance that is largely innate. This true recognition has facilitated the evolution of very rapid hatchling rejection and, in turn, striking visual mimicry of host young by little-bronze cuckoo chicks.布谷鸟将卵产于其他鸟类的巢中，雏鸟破壳后会将同巢其他幼体逐出巢外，独占宿主亲鸟的抚育。理论预测，宿主不会演化出识别并排斥布谷鸟雏鸟的能力，因为存在如下风险：在第一窝雏鸟抚育阶段，宿主会错误地对布谷鸟雏鸟产生印随印记，进而在后续繁殖中持续排斥自身的雏鸟。然而近期研究表明，部分宿主确实会将巢内的布谷鸟雏鸟排斥出巢，这意味着这些宿主的识别系统要么不依赖第一窝印随印记，要么使用独立于雏鸟表型的识别线索。本研究以小铜色杜鹃（Chalcites minutillus）的宿主——巨嘴噪刺莺（Gerygone magnirostris）为研究对象，探讨其雏鸟排斥行为的近因机制。研究结果显示，巨嘴噪刺莺至少基于一种视觉雏鸟性状（雏鸟绒羽覆盖量）采用真正的模板式识别，且该识别过程还会受到产卵期巢内成年布谷鸟出现经历的调控。鉴于通过印随印记获取识别模板存在理论层面的限制，巨嘴噪刺莺必然拥有一套先天主导的自身雏鸟外观识别模板。这种真正的模板识别能力推动了极快速雏鸟排斥行为的演化，进而促使小铜色杜鹃雏鸟演化出针对宿主幼鸟的显著视觉拟态。