中国多杜鹃寄生系统中杜鹃和洞巢鸟类的协同进化研究

Phylogenetically widespread in arthropods, fishes, and birds, brood parasitism is a breeding strategy in which a parasite manipulates a host to raise its offspring. It provides tractable systems for studying coevolutionary processes in nature and has been attracting much attention in behavioral ecology and evolutionary biology. .In one example of this scenario, avian brood parasites, e.g. cuckoos, lay their eggs in the nests of other bird species (hosts) and rely on foster parents to care for their parasitic young. Interactions between cuckoos and their hosts are model systems and textbook examples of co-evolutionary arms races, in which there is a strong selective pressure on hosts to evolve defences against brood parasites, and in turn would select for the brood parasite to evolve adaptive counter defences, leading to selection for improved host defences and further parasitic adaptations. Reciprocal adaptations can occur at all stages of the nesting cycle, including nest defence, egg recognition and egg rejection, chick discrimination, and fledgling abandonment, with the two latter stages receiving the least research attention. .Coevolutionary theory predicts that the long-term outcome of the relationships between brood parasites and their hosts should be coevolutionary cycles based on a dynamic change selecting the currently least-defended host species, given that when well-defended hosts are abandoned, hosts will be selected to decrease their defences as these are usually assumed to be costly. .In light of both coevolutionary processes (cycles and alternation) theory, the proposal focuses on cavity nesting birds in a multiple-cuckoo species parasitism system in China, aims to test the light environment hypothesis, the cryptic cuckoo egg hypothesis and the rarer enimy hypothesis, and examines coevolved adaptations and counteradaptations in cuckoos and hosts at all stages of the host nesting cycle: those that precede laying of the parasitic egg and those at the egg, chick, and fledgling stages..It has been suggested that cavity nesting is a recently evolved trait to avoid cuckoo parasitism. Poorly accessible nest sites represent a unique challenge to the laying of cuckoos, and cavity nesting seems likely to decrease the costs associated with cuckoo parasitism for hosts. However, the benefits of using cavities as a defence against brood parasites, effect of UV and nest luminosity on egg and nestling recognition, evolution of egg polymophism, and mechanism of chick and fledgling discrimination in cavity nesting birds need investigation. Ongoing efforts to document the diversity of host defenses and parasite offenses will facilitate understanding of coevolutionary processes and the ecological consequences of species interactions in nature.

巢寄生行为在昆虫、鱼类和鸟类均有发现，是行为生态学和进化生物学研究的热点问题之一。鸟类巢寄生中寄生性鸟类如杜鹃与其宿主之间的种间互作，是研究协同进化的模式系统，两者的协同进化可发生于宿主生活史的各个阶段，包括巢防御、卵拒绝、雏鸟识别和雏鸟遗弃等，但在雏鸟识别和雏鸟遗弃等方面的工作还非常少。本项目利用中国多杜鹃寄生系统的资源优势，选取目前国际上研究相对薄弱、实验操作相对容易控制的洞巢鸟类作为研究对象，通过验证光环境假说、杜鹃卵隐蔽假说和无敌难以进化假说等，分别从杜鹃对洞巢鸟类的宿主选择和洞巢鸟类的巢防御、洞巢鸟类卵色多态性的适应意义、光照度和紫外光（UV）对洞巢鸟类卵识别与卵拒绝以及雏鸟识别的影响、洞巢鸟类的雏鸟识别机制及其进化等方面，探讨杜鹃的寄生策略以及宿主的反寄生对策，填补光照度对宿主卵拒绝和雏鸟识别的影响这一研究空白，以深化人们对鸟类与其宿主协同进化关系的认识。

本项目利用中国多杜鹃寄生系统的资源优势，选取洞巢鸟类作为研究对象，探讨杜鹃的寄生策略以及宿主的反寄生对策，以深化人们对鸟类与其宿主协同进化关系的认识。我们的研究发现，分布范围涵盖南方小型杜鹃种类即东洋界的广布洞巢鸟类具有识别寄生性杜鹃和外来寄生卵的能力，而分布于古北界的洞巢鸟类宿主不具备或具备较低的卵识别能力，这表明杜鹃寄生是洞巢鸟类宿主巢防御行为（反寄生策略）和卵色多态性进化的重要选择压力；洞巢鸟类宿主的卵回收行为和卵识别行为具有明显的冲突和决策权衡，这开辟了鸟类巢寄生新的研究领域和方向；卵斑点是洞巢鸟类识别和拒绝外来卵的重要线索，具有信号功能；对麻雀属（Passer spp.）洞巢鸟类的研究表明，它们不识别外来寄生卵，但却进化出了识别外来雏鸟的能力，而营开放巢的鸟类却没有识别雏鸟的能力，结果支持“无敌难以进化”假说，拓展了鸟类巢寄生协同进化的研究领域。

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