Department of Natural Resources and Environmental Sciences, University of Illinois at Urbana-Champaign, Urbana, IL 61801;
Illinois Natural History Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, Champaign, IL 61801.
Proc Natl Acad Sci U S A. 2020 Dec 1;117(48):30539-30546. doi: 10.1073/pnas.2008955117. Epub 2020 Nov 16.
Parent-offspring conflict has explained a variety of ecological phenomena across animal taxa, but its role in mediating when songbirds fledge remains controversial. Specifically, ecologists have long debated the influence of songbird parents on the age of fledging: Do parents manipulate offspring into fledging to optimize their own fitness or do offspring choose when to leave? To provide greater insight into parent-offspring conflict over fledging age in songbirds, we compared nesting and postfledging survival rates across 18 species from eight studies in the continental United States. For 12 species (67%), we found that fledging transitions offspring from comparatively safe nesting environments to more dangerous postfledging ones, resulting in a postfledging bottleneck. This raises an important question: as past research shows that offspring would benefit-improve postfledging survival-by staying in the nest longer: Why then do they fledge so early? Our findings suggest that parents manipulate offspring into fledging early for their own benefit, but at the cost of survival for each individual offspring, reflecting parent-offspring conflict. Early fledging incurred, on average, a 13.6% postfledging survival cost for each individual offspring, but parents benefitted through a 14.0% increase in the likelihood of raising at least one offspring to independence. These parental benefits were uneven across species-driven by an interaction between nest mortality risk and brood size-and predicted the age of fledging among species. Collectively, our results suggest that parent-offspring conflict and associated parental benefits explain variation in fledging age among songbird species and why postfledging bottlenecks occur.
亲代-后代冲突解释了动物分类群中多种生态现象，但它在调节鸣禽何时离巢的作用仍存在争议。具体来说，生态学家长期以来一直在争论鸣禽父母对离巢年龄的影响：父母是否操纵后代离巢以优化自己的适应性，还是后代选择何时离开？为了更深入地了解鸣禽离巢年龄的亲代-后代冲突，我们比较了来自美国大陆 8 项研究的 18 个物种的筑巢和离巢后存活率。对于 12 个物种（67%），我们发现离巢将后代从相对安全的筑巢环境转移到更危险的离巢后环境，导致离巢后瓶颈。这提出了一个重要的问题：过去的研究表明，后代通过在巢中停留更长时间来受益——提高离巢后的存活率：那么它们为什么要这么早离巢呢？我们的研究结果表明，父母为了自己的利益而操纵后代早期离巢，但代价是每个后代的生存，反映了亲代-后代的冲突。平均而言，每个后代的早期离巢会导致离巢后 13.6%的存活率降低，但父母通过将至少一只后代抚养至独立的可能性增加 14.0%而受益。这些亲代利益在物种之间是不均匀的——这是巢死亡率风险和育雏大小之间相互作用的结果——并预测了物种之间的离巢年龄。总的来说，我们的研究结果表明，亲代-后代冲突和相关的亲代利益解释了鸣禽物种离巢年龄的变化，以及为什么会发生离巢后瓶颈。
