Female differential allocation in response to extra-pair offspring and social mate attractiveness

Renewed debate over what benefits females might gain from producing extra-pair offspring emphasizes the possibility that apparent differences in quality between within-pair and extra-pair offspring are confounded by greater maternal investment in extra-pair offspring. Moreover, the attractiveness of a female's social mate can also influence contributions of both partners to a reproductive attempt. Here we explore the complexities involved in parental investment decisions in response to extra-pair offspring and mate attractiveness with a focus on the female point of view. Adult zebra finches paired and reproduced in a colony setting. A male's early-life diet quality and his extra-pair reproductive success were used as metrics of his mating attractiveness. Females paired with males that achieved extra-pair success laid heavier eggs than other females and spent less time attending their nests than their mates or other females. Extra-pair nestlings were fed more protein-rich hen's egg than within-pair nestlings. Females producing extra-pair offspring had more surviving sons than females producing only within-pair offspring. Collectively, results show that females differentially allocate resources in response to offspring extra-pair status and their social mate's attractiveness. Females may also obtain fitness benefits through the production of extra-pair offspring.

关于雌性产出婚外配后代（extra-pair offspring）所能获得的益处的新一轮学术争论，凸显了这样一种可能性：雌性对婚外配后代投入更多母体投入（maternal investment），会混淆婚内后代（within-pair offspring）与婚外配后代之间看似存在的质量差异。此外，雌性社会配偶（social mate）的吸引力，也会影响配偶双方对繁殖尝试的投入程度。本研究围绕雌性视角，探讨雌性在应对婚外配后代与配偶吸引力时，亲本投入（parental investment）决策所涉及的复杂机制。实验以群居环境中配对繁殖的成年斑胸草雀为研究对象，以雄性个体的早期日粮质量及其婚外配繁殖成功率作为其交配吸引力的衡量指标。研究结果表明，与取得婚外配成功的雄性配对的雌性，所产的卵重量高于其他雌性，且其照料巢穴的时长不仅低于其配偶，也低于其他雌性个体；相较于婚内雏鸟，婚外配雏鸟获得的高蛋白鸡蛋饲喂量更高；产下婚外配后代的雌性，其存活的雄性子代数量多于仅产下婚内后代的雌性。综合来看，雌性会根据子代的婚外配身份以及其社会配偶的吸引力，差异化地分配繁殖资源。雌性或可通过产出婚外配后代，获得进化适合度（fitness）收益。