High level of extrapair fertilizations in individual Tibetan azure-winged magpies and their adaptive responses

Extrapair fertilizations (EPFs) occur widely in socially monogamous birds and result in mixed parentage in the brood. The response of an individual to these EPFs of its social mate remains poorly investigated in terms of parental care for the mixed brood. We addressed this question in a cooperatively-breeding corvid, the azure-winged magpie Cyanopica cyana. Parentage analysis indicated that 45% of females and 37% of males engaged in EPFs. There were 49% of cooperative groups and 36% of bi-parental nests with extrapair paternity (EPP) offspring, and 22% of cooperative groups and 19% of bi-parental nests with extrapair maternity (EPM) offspring. Based on the identity of offspring, we classified adults into four types: EPP offspring fathers/mothers, EPM offspring fathers/mothers, cuckolded males/females, and faithful males/females. A comparison of provisioning rates among all four types of breeders showed that 1) EPM offspring fathers had the highest provisioning rate; 2) cuckolded males did not reduce parental care, compared to faithful males and EPP offspring fathers; and 3) females of different types did not differ in their provisioning rates. Our findings suggest that a combination of frequent opportunities, low costs of cuckoldry, and the benefits of establishing a cooperative neighbourhood can explain why EPFs occur frequently in the Tibetan population of azure-winged magpie.

额外配对受精（extrapair fertilizations, EPFs）广泛存在于社会单配制鸟类中，会导致雏鸟窝出现混合亲权现象。目前针对混合亲权雏鸟的育幼行为，个体对其社会配偶发生额外配对受精的应对策略仍未得到充分研究。本研究以合作繁殖的鸦科鸟类——蓝翅喜鹊（Cyanopica cyana）为研究对象，探讨了这一科学问题。亲权鉴定结果显示，45%的雌性和37%的雄性存在额外配对受精行为。存在额外配对父权（extrapair paternity, EPP）后代的合作繁殖群和双亲巢占比分别为49%和36%；存在额外配对母权（extrapair maternity, EPM）后代的合作繁殖群和双亲巢占比则分别为22%和19%。根据后代的亲权归属，研究将成年个体划分为四类：额外配对父权后代的父/母、额外配对母权后代的父/母、被婚外配的雄/雌个体，以及忠实的雄/雌个体。对四类繁殖个体的育雏投喂率进行比较后发现：1）额外配对母权后代的雄性亲本投喂率最高；2）与忠实雄性和额外配对父权后代的雄性亲本相比，被婚外配的雄性并未降低其育幼投入；3）不同类型的雌性亲本在育雏投喂率上并无显著差异。本研究结果表明，频繁的婚外配机会、被婚外配的低代价，以及构建合作社群带来的收益，共同解释了为何蓝翅喜鹊西藏种群中额外配对受精现象如此普遍。