Data from: Egg investment in response to the helper presence in cooperatively breeding Tibetan ground tits

Life-history theory predicts a trade-off between current and future reproduction to maximize lifetime fitness. In cooperatively breeding species, where offspring care is shared between breeders and helpers, helper presence may influence the female breeders’ egg investment, and consequently, survival and future reproductive success. For example, female breeders may reduce egg investment in response to helper presence if this reduction is compensated by helpers during provisioning. Alternatively, female breeders may increase egg investment in response to helper presence if helpers allow the breeders to raise more or higher quality offspring successfully. In the facultatively cooperative-breeding Tibetan ground tit Pseudopodoces humilis, previous studies found that helpers improve total nestling provisioning rates and fledgling recruitment, but have no apparent effects on the number and body mass of fledglings produced, while breeders with helpers show reduced provisioning rates and higher survival. Here, we investigated whether some of these effects may be explained by female breeders reducing their investment in eggs in response to helper presence. In addition, we investigated whether egg investment is associated with the female breeder’s future fitness. Our results showed that helper presence had no effect on the female breeders’ egg investment, and that egg investment was not associated with breeder survival and reproductive success. Our findings suggest that the responses of breeders to helping should be investigated throughout the breeding cycle, because the conclusions regarding the breeders’ adjustment of reproductive investment in response to being helped may depend on which stage of the breeding cycle is considered.

生活史理论（life-history theory）预测，以实现终身适合度最大化，个体需在当前繁殖与未来繁殖之间权衡取舍。在育幼行为由繁殖亲体与协助者共同分担的合作繁殖物种（cooperatively breeding species）中，协助者的存在可能影响雌性繁殖亲体的卵投入，进而影响其存活与未来繁殖成功率。
例如，若协助者在育雏投喂阶段可弥补雌性繁殖亲体的投入缩减，那么雌性繁殖亲体或会因协助者的存在而降低卵投入；反之，若协助者可助力繁殖亲体成功抚育更多或质量更优的后代，雌性繁殖亲体则可能增加卵投入。
针对兼性合作繁殖的西藏地山雀（Pseudopodoces humilis），既往研究表明，协助者可提升雏鸟总投喂率与出飞幼鸟的招募成功率，但对产出幼鸟的数量与体质量无显著影响；而带有协助者的繁殖亲体则表现出育雏投喂率降低、存活率升高的特征。
本研究旨在探究，上述部分效应是否可通过雌性繁殖亲体因协助者存在而降低卵投入这一机制得到解释。此外，本研究还分析了卵投入与雌性繁殖亲体未来适合度之间的关联。
研究结果显示，协助者的存在对雌性繁殖亲体的卵投入无显著影响，且卵投入与繁殖亲体的存活率及繁殖成功率均无显著关联。
本研究结果提示，应在完整繁殖周期内探究繁殖亲体对协助抚育行为的响应，因为针对繁殖亲体响应协助行为而调整繁殖投入的相关结论，可能取决于所考察的繁殖周期阶段。