Data from: Extra-pair paternity is not driven by inbreeding avoidance and does not affect provisioning rates in a cooperatively breeding bird, the noisy miner (Manorina melanocephala)

In many socially monogamous bird species, both sexes regularly engage in mating outside their pair bond. While the benefits of extra-pair (EP) mating behavior are clear and well established for males, such as an increase in the number of sired offspring, the benefits of EP mating behavior to females are less clear. A dominant theory for the incidence of EP mating is that socially monogamous females can improve the genetic quality of their offspring and avoid the costs of inbreeding through EP mating. In addition, in cooperatively breeding species, the theory of ‘parental care’, predicts that females obtain additional help for their offspring through extra-pair matings. Here, we examined evidence for both the inbreeding avoidance and parental care hypotheses in the cooperatively breeding noisy miner (Manorina melanocephala). Overall, EP mating occurred in 27% of broods, with 14% of offspring sired by males other than the identified pair-bonded male. There was a strong tendency to avoid pairing with genetically related individuals, with 86% of breeding pairs being significantly less related to each other than the general population. The occurrence of extra-pair paternity was independent of the degree of relatedness between the pair. Provisioning patterns in relation to EP mating was not consistent with the ‘parental care’ hypothesis and EP males did not contribute to the care of broods. These results demonstrate that in this system, there is no evidence that EP mating might function as a mechanism to reduce the costs of inbreeding depression or to gain benefits of extra helpers.

在诸多社会一夫一妻制鸟类（socially monogamous bird species）中，两性均会频繁发生配对关系外的交配行为。对于雄性而言，婚外配（extra-pair mating, EP）行为的益处清晰且已得到充分证实——例如可提升自身繁育后代的数量；但这类行为对雌性的益处却尚不明确。针对婚外配发生频率的主流理论认为，社会一夫一妻制的雌性可通过婚外配行为提升后代的遗传质量，并规避近交成本。此外，在合作繁殖物种中，「亲代照料」（parental care）假说预测雌性可通过婚外配为后代获得额外的抚育帮助。本研究针对合作繁殖的噪吸蜜鸟（Manorina melanocephala），检验了近交规避与亲代照料这两个假说的相关证据。整体而言，27%的繁殖窝存在婚外配现象，其中14%的后代由配对雄性以外的雄性繁育。研究发现，个体存在强烈的规避与遗传相关个体配对的倾向：86%的繁殖配对个体间的遗传相关度显著低于种群平均水平。婚外父权（extra-pair paternity）的发生与配对个体间的遗传相关度无关。针对婚外配的育雏投喂模式并不符合「亲代照料」假说，且婚外配雄性并未参与后代的抚育工作。本研究结果表明，在该物种的繁殖系统中，尚无证据显示婚外配行为可作为降低近交衰退（inbreeding depression）成本或获得额外抚育者帮助的机制。