Decoupling of growth, physiological state, and subsequent performance in a developmentally manipulated songbird

It is generally assumed that larger juveniles are more physiologically mature, hence their overall condition and subsequent performance are higher. Yet, some taxa face extreme workload transitions during development (e.g., nest departure in birds), which may select for non-linear growth profiles that decouple relationships between body size and physiological state, making associations between development and juvenile performance uncertain. We manipulated perceived mass in European starlings approaching fledging using 4.0 g weighted backpacks, measuring subsequent growth trajectories (mass, wing length) and physiological state (aerobic capacity, energy state, oxidative status) to test whether body size and physiology are developmentally coupled during a non-linear growth phase (pre-fledging mass recession). Nanotag radio transmitters were then used to track post-fledging performance (activity, activity-slope, dispersal). Weighted nestlings had greater pre-fledging mass recession and lower oxidative status than controls, but equal aerobic capacity and energy state. Haemoglobin and dROMs, as well as metrics of growth and body size, predicted post-fledging performance in control birds, whereas weighted birds showed no correlation between fledgling state and performance. Our data suggest mass-independent development of some physiological traits in species with non-linear growth profiles, potentially with a context-dependent oxidative cost, and that physiology (not just body size) may predict post-fledging performance.

学界普遍认为体型更大的幼体生理成熟度更高，因此其整体健康状况与后续表现也更为优异。然而，部分分类群在发育过程中会经历极端的发育负荷转变（例如鸟类的离巢行为），这可能促使自然选择偏向演化出非线性生长模式，使得体型大小与生理状态之间的关联被解耦，进而导致发育进程与幼体表现之间的关联变得难以确定。本研究针对即将进入离巢期的欧椋鸟，通过为其背负4.0克负重背包以操控其感知体重，随后测量其生长轨迹（体重、翼长）与生理状态（有氧能力、能量状态、氧化状态（oxidative status）），以此验证在非线性生长阶段（离巢前体重下降期），体型大小与生理机能是否在发育过程中存在耦合关系。随后研究人员借助纳米标签无线电发射器，追踪幼鸟离巢后的表现（活动水平、活动变化斜率、扩散行为）。背负负重的雏鸟相较于对照组，离巢前的体重下降幅度更大，氧化状态更差，但二者的有氧能力与能量状态并无显著差异。对照组雏鸟的血红蛋白（Haemoglobin）、活性氧代谢产物（dROMs）以及生长与体型相关指标，均可预测其离巢后的表现；而负重组雏鸟的离巢前生理状态与后续表现之间则无显著关联。本研究数据表明，在具有非线性生长模式的物种中，部分生理性状的发育不受体重影响，且可能存在依赖于环境背景的氧化应激成本；同时，生理状态（而非仅体型大小）或可预测幼鸟离巢后的表现。