Data_Sheet_1_Distribution of Experimentally Increased Costs of Parental Care Among Family Members Depends on Duration of Offspring Care in Biparental Birds.docx

Biparental care systems are a valuable model to examine conflict, cooperation, and coordination between unrelated individuals, as the interactions between the parents determines their fitness. Temporarily handicapping one parent induces a higher cost of providing care and is a widespread experimental technique for testing coordinated responses to changes in the costs of parental care in birds. However, dissimilarity in experimental designs of handicapping studies has hindered interspecific comparisons of the patterns of cost distribution between parents and their offspring. Here we apply a comparative approach by handicapping a parent at nests of five altricial bird species using the same experimental treatment. Across species, handicapped parents reduced their nest visitation rate, indicating increased costs of parental care for the manipulated parent. Unexpectedly, the partners of handicapped individuals did not compensate for the reduction in care, and the increased costs were subsequently passed to their offspring. The strength of this effect was mediated by the total duration of offspring care; in species with long care periods, the offspring were passed a greater share of the additional cost. This effect was evident in both changes to nest visitation rates and the body mass gain of the nestlings. Surprisingly, these responses were independent of life history pace (i.e., adult survival and fecundity). While most studies of the costs of parental care focus on the trade-off between current and future reproduction or survival (intra-individual trade-offs), our study highlights that a greater attention to inter-generational trade-offs is warranted, particularly in species with prolonged parental care. Moreover, our findings demonstrate that parental care decisions may be weighed more against physiological workload constraints than against future prospects of reproduction, supporting evidence that avian species may devote comparable amounts of energy into survival, regardless of life history pace.

双亲抚育体系是研究无血缘个体之间冲突、合作与协调的宝贵模型，因为父母的互动决定了其适应性。暂时削弱某一父母的抚育能力会导致抚育成本上升，这是在鸟类中测试对父母抚育成本变化协调反应的一种普遍实验技术。然而，由于削弱研究实验设计的不一致性，阻碍了对不同物种间父母与后代之间成本分配模式进行比较。在本研究中，我们采用比较方法，通过对五种晚成鸟类的巢穴中的父母进行相同实验处理以削弱其抚育能力。跨物种而言，被削弱抚育能力的父母降低了其巢穴访问率，表明对操作父母的抚育成本有所增加。出人意料的是，被削弱个体的伴侣并未对抚育减少进行补偿，额外的成本随后转移给了后代。这种效应的强度由后代抚育的总持续时间介导；在抚育周期较长的物种中，后代承担了更大的额外成本份额。这种效应在巢穴访问率的变化和雏鸟体重增加方面均有体现。令人惊讶的是，这些反应与生命周期速度（即成年生存率和繁殖力）无关。虽然大多数关于父母抚育成本的研究都关注当前与未来繁殖或生存之间的权衡（个体内权衡），但我们的研究强调了有必要更加关注代际权衡，尤其是在抚育期较长的物种中。此外，我们的发现表明，父母抚育决策可能更多地受到生理工作负荷限制的影响，而不是未来繁殖前景的影响，这支持了鸟类物种可能在不同生命周期速度下投入相当能量用于生存的证据。