备选繁殖策略对灰喜鹊终身繁殖成功的影响

Alternative breeding strategies, including delayed reproduction, cooperative breeding, extra-pair copulations and divorce, have been frequently adopted by breeders of birds. Though it has been widely accepted that those alternative strategies can influence the output of current reproduction, we know less about their effects on the lifetime reproductive success (LRS) of birds. In this project, we will explore how these four alternative strategies influence the LRS of a cooperatively-breeding corvid, the azure-winged magpie Cyanopica cyana, based on a long-term data about individual banding and monitoring. Through tracing the origin and identity of helpers within cooperative groups, we can compare the breeding performance of helpers and their nest-mates to examine whether delayed reproduction has a positive effect on the LRS of helpers. By investigating how the dominant pair of cooperative group balances the benefits and costs of enlisting extra individuals as helpers, we can illustrate how cooperative breeding may occur under special environmental conditions. In order to find out both short- and long-term effects of engaging in extra-pair copulations on the reproduction, we need to compare the current reproductive success of a cuckolding individual with its breeding performance in subsequent season. Finally, we want to prove that there is an aging effect on the divorce decision by two means. One is to analyze the tendency of an individual’s breeding performance with aging; the other is to determine the age of intact and new social mates of a divorced breeder. Over the course of the project, we will design some experiments, such as artificial feeding, predator introduction and modification of phenotypic traits, to adjust the quality of both individual breeder and territory. Then, we may know how an individual makes response to the dynamics of ecological factors by changing its alternative breeding strategy.

鸟类繁殖中，备选繁殖策略经常被采用，包括繁殖延迟、繁殖合作、婚外交配和离婚。这些备选策略能显著影响个体单次繁殖的产出，但对其终身繁殖成功的影响还缺少足够证据。本项目基于长期个体标记和监测的数据，在合作繁殖的鸟类——灰喜鹊中，研究四种备选策略对个体终身繁殖成功的影响。通过追溯帮助者的来源和身份、比较帮助者与其同巢同胞的繁殖表现，分析繁殖延迟能够提高个体的终身繁殖成功。通过分析合作群内的优势繁殖者如何权衡招募帮助者的利益和代价，解释繁殖合作策略与环境因子的关系。通过比较婚外交配策略者当年繁殖成功和来年的繁殖表现，检测婚外交配对繁殖产出的短期和长期效应。通过分析个体繁殖表现随年龄增长的变化趋势、比较个体离婚前、后的配对年龄结构来检验离婚策略是否存在年龄效应。在研究过程中，我们将通过人工递食实验、天敌模拟实验、以及表型修饰等方法来调控个体及领域质量，分析备选繁殖策略如何对生态因子的波动做出回应。

在本项目中，我们研究了在青藏高原上繁殖的灰喜鹊的备选繁殖策略，包括婚外交配（EPCs）、合作繁殖和离婚。亲权鉴定结果显示，45%的雌性和37%的雄性发生过EPCs，这一策略既造成了婚外父权（EPP）又造成了婚外母权（EPM）。根据后代的身份及所在的巢，成鸟可分为四种类型：EPP后代的遗传父、母，EPM后代的遗传父、母，被戴绿帽的雌、雄，以及忠实的雌、雄。比较四种成鸟之间的递食率发现：1）EPM后代的遗传父递食率最高；2）相对于忠实的雄性，被戴绿帽子的雄性的递食率并未显著降低；3）四种雌性间的递食率无显著差异。此外，我们还发现：1）在EPP中被戴绿帽的雄性和在EPM中被戴绿帽的雌性养活的出飞后代显著小于被忠实的个体养活的出飞后代；2）相对于忠实的繁殖者，被戴绿帽的个体在其巢内无非婚生后代时会提高亲本抚育，而在巢内有非婚生后代时并没有显著降低亲本抚育。雌性发生EPC可能是一个繁殖对离婚的主要原因。一旦离婚，雌性与初婚的雄性重配对后实现的繁殖成功显著高于与已婚的雄性重配对后的繁殖成功，然而雄性恰好相反，他们与已婚的雌性重配对后实现的繁殖成功要高于与初婚的雌性重配对后的繁殖成功。离婚的雌性（而不是雄性）与无经验的个体重配对后能够获得更多的EPC机会；同时，离婚的雌性的递食率比无经验的雌性的递食率更低而离婚的雄性与无经验的雄性之间无显著差异。因此，我们认为雌性可能是灰喜鹊中离婚事件的主动发起者，因为她们更可能与无经验的雄性重新配对并在未来的繁殖中获得更大优势。至于合作繁殖策略，我们发现在一个集群里合作繁殖者所占比例与这个集群向高原殖民的时间及营巢饱和度显著相关。在个体水平上，一个繁殖对是否雇用帮助者仅与它们的营巢开始时间有关——一个繁殖对开始营巢的时间越晚，它们雇用帮助者的概率越低。综上所述，本项目的这些研究结果表明，高原繁殖的灰喜鹊选择哪种备选繁殖策略是综合生态环境因子与自身体况之后的结果。