两种共域山鹪莺对杜鹃巢寄生的反寄生策略

Avian brood parasitism as a specific breeding strategy, the parasite generally transfers the rearing obligation to their hosts which would suffer enormous costs from egg incubation and nestling rearing. These hosts will evolve an adaptation to increase their fitness, according to egg discrimination and rejection of the foreign parasitic egg to defense against brood parasitism. Hence, the reciprocal interaction is a good model system for coevolution research. The proposed study will compare anti-parasitism strategies to cuckoo parasitism in two sympatric prinia hosts, the yellow bellied prinia Prinia flaviventris and plain prinia P. inornata, under the single-cuckoo parasitism system in Taiwan Island with that of the multiple-cuckoo parasitism system in mainland China. Such anti-parasitism adaptations include nest defense, egg recognition ability, egg cognitive mechanism and recognition cues, variation of clutch size and life history traits. These investigations would significantly improve our knowledge of adaptation and counter-adaptation in the arms race between parasites and their hosts under different selection pressure.

鸟类巢寄生作为一种特殊的繁殖行为，寄生者通过让其它个体为其抚养后代而致使寄主蒙受巨大代价，许多寄主为此进化出识别并拒绝寄生卵或雏鸟等反寄生对策来提高适合度，两者之间的相互作用过程是研究协同进化的一个模式系统。本研究通过对黄腹山鹪莺（Prinia flaviventris）和纯色山鹪莺（P. inornata）在中国大陆的多杜鹃寄生系统和台湾的中杜鹃（Cuculus optatus）单一寄生系统的比较，从对寄生杜鹃的巢防御、卵识别能力、识别线索和识别机制、窝卵数变异及其繁殖生活史特征等方面揭示两种山鹪莺的反寄生策略及其进化适应性，以丰富和深化人们对于鸟类巢寄生中寄生者与寄主之间在不同寄生选择压力下的协同进化的理解。

巢寄生者与宿主的协同进化过程中，识别并拒绝外来寄生卵是宿主防御巢寄生最为有效的行为适应。本研究对黄腹山鹪莺（Prinia flaviventris）和纯色山鹪莺（P. inornata）两种同域鸟类在中国大陆和台湾两个不同杜鹃寄生压力环境下对外来卵的识别能力和拒绝率进行了比较。结果表明，宿主在寄生压力较大的情况下，卵识别能力较强，对外来卵的拒绝率较高，退出寄生系统后，对外来卵的拒绝能力会急剧下降。两种山鹪莺在寄生系统中进化出比非寄生系统较低的卵窝内变异和较高的卵窝间变异，且纯色山鹪莺在寄生压力较大的大陆进化出多态型卵，而寄生压力较小的台湾种群只产单一型卵。我们通过对黄腹鹪莺卵的钝端和尖端采取涂斑点的方式，用以检测和比较寄生和非寄生两个种群对钝端识别信号的反应。结果显示，寄生状态下的种群对钝端的拒绝率极显著高于尖端，而在非寄生种群中两者则没有差异，无论钝端或尖端均全部接受实验卵，这可能与没有寄生压力后卵识别能力的下降有关。我们比较了黄腹山鹪莺纯色山鹪莺两种宿主鸟类对寄生杜鹃的防御行为反应。结果表明，在多杜鹃和单杜鹃寄生系统中，两种山鹪莺能区别对待不同的寄生杜鹃。单一系统能准确识别并攻击，而多杜鹃系统则主要通过卵识别等方式来拒绝杜鹃的寄生。