Gill Lisa F, van Schaik Jaap, von Bayern Auguste M P, Gahr Manfred L
Department of Behavioural Neurobiology, Max Planck Institute for Ornithology, Eberhard-Gwinner-Strasse, Seewiesen, Germany.
Department of Applied Zoology and Nature Conservation, University of Greifswald, Greifswald, Germany.
Behav Ecol. 2020 Jan-Feb;31(1):247-260. doi: 10.1093/beheco/arz185. Epub 2019 Nov 22.
"Monogamy" refers to different components of pair exclusiveness: the social pair, sexual partners, and the genetic outcome of sexual encounters. Avian monogamy is usually defined socially or genetically, whereas quantifications of sexual behavior remain scarce. Jackdaws () are considered a rare example of strict monogamy in songbirds, with lifelong pair bonds and little genetic evidence for extrapair (EP) offspring. Yet jackdaw copulations, although accompanied by loud copulation calls, are rarely observed because they occur visually concealed inside nest cavities. Using full-day nest-box video surveillance and on-bird acoustic bio-logging, we directly observed jackdaw sexual behavior and compared it to the corresponding genetic outcome obtained via molecular parentage analysis. In the video-observed nests, we found genetic monogamy but frequently detected forced EP sexual behavior, accompanied by characteristic male copulation calls. We, thus, challenge the long-held notion of strict jackdaw monogamy at the sexual level. Our data suggest that male mate guarding and frequent intrapair copulations during the female fertile phase, as well as the forced nature of the copulations, could explain the absence of EP offspring. Because EP copulation behavior appeared to be costly for both sexes, we suggest that immediate fitness benefits are an unlikely explanation for its prevalence. Instead, sexual conflict and dominance effects could interact to shape the spatiotemporal pattern of EP sexual behavior in this species. Our results call for larger-scale investigations of jackdaw sexual behavior and parentage and highlight the importance of combining social, sexual, and genetic data sets for a more complete understanding of mating systems.
“一夫一妻制”指配偶排他性的不同组成部分：社会配偶、性伴侣以及性接触的遗传结果。鸟类的一夫一妻制通常从社会层面或基因层面来定义，而关于性行为的量化研究仍然很少。寒鸦被认为是鸣禽中严格一夫一妻制的罕见例子，它们有着终生配偶关系，且几乎没有基因证据表明存在婚外（EP）后代。然而，寒鸦的交配行为，尽管伴随着响亮的交配叫声，但却很少被观察到，因为它们发生在巢穴内部，视觉上难以察觉。通过对巢箱进行全天视频监控以及对鸟类进行声学生物记录，我们直接观察了寒鸦的性行为，并将其与通过分子亲子鉴定获得的相应遗传结果进行了比较。在视频观察的巢穴中，我们发现了基因层面的一夫一妻制，但频繁检测到强迫性的婚外性行为，同时伴有典型的雄性交配叫声。因此，我们在性层面挑战了长期以来关于寒鸦严格一夫一妻制的观念。我们的数据表明，在雌性的排卵期，雄性的配偶守护行为以及频繁的配偶间交配，再加上交配行为的强迫性质，可以解释婚外后代不存在的原因。由于婚外交配行为对两性来说似乎都代价高昂，我们认为直接的适应性益处不太可能解释其普遍存在的原因。相反，性冲突和支配效应可能相互作用，从而塑造了该物种婚外性行为的时空模式。我们的研究结果呼吁对寒鸦的性行为和亲子关系进行更大规模的调查，并强调了结合社会、性和基因数据集以更全面理解交配系统的重要性。
