Data from: Causal link between insulin-like growth factor 1 and growth in nestlings of a wild passerine bird

Life history of animals is strongly linked with the variability in postnatal growth rates, because the ability to achieve necessary body mass early in life is directly connected with the ability to survive and reproduce later in life. Surprisingly, little is known about the physiological mechanisms connecting food availability with the variability of growth in wild animals. We used a hormonal injection treatment in free-living nestlings of the pied flycatcher (Ficedula hypoleuca). In doing this, we aimed to see how their plasma insulin-like growth factor 1 (IGF-1) levels and its mediation of growth rate vary in response to administration of exogenous IGF-1 during the early period of postnatal development. We showed that the levels of IGF-1 as well as growth rate and body size, in terms of body mass and tarsus length, were significantly higher in IGF-1-injected nestlings, compared with those in the control group. These differences became especially pronounced from day 7 post-hatch onwards during the 13-day nestling period. Additionally, the proportional investment into growth was more profoundly downregulated in IGF-1-injected nestlings at the end of the nestling period, which achieved fledging size earlier, compared with control nestlings. Our results are the first to highlight IGF-1 as the causal link between growth conditions and variability of growth rate and body size in wild vertebrates. Interestingly, the change in IGF-1 levels also showed a plausible, distinct adaptive age- and physical maturity-dependent pattern in nestlings to match the benefits gained by them when investing in growth, with the cost endured during the early days of postnatal development to maximize their fitness. Therefore, this mechanism might be among those mediating the maintenance of genetic variability in growth rates in populations, presumably regardless of the presence of strong directional selection acting upon them.

动物的生活史与产后生长速率的变异密切相关，因为生命早期获得必要体质量的能力，直接关联到后续存活与繁殖的能力。令人颇感意外的是，学界对于连接食物可获得性与野生动物生长变异的生理机制仍所知寥寥。我们对自由生活的斑鹟（Ficedula hypoleuca）雏鸟开展了激素注射处理实验，旨在探究在产后发育早期阶段，其血浆胰岛素样生长因子1（insulin-like growth factor 1, IGF-1）水平以及生长速率的介导效应，会如何响应外源性IGF-1的施加。研究结果显示，相较于对照组，注射IGF-1的雏鸟其IGF-1水平、生长速率以及以体质量和跗跖长度衡量的身体体型均显著更高；在为期13天的雏鸟育雏期内，这些差异自孵化后第7天起愈发显著。此外，在育雏期结束时，注射IGF-1的雏鸟对生长的比例投入受到更为显著的下调，且相较于对照组雏鸟，它们更早达到了离巢体型。本研究首次阐明IGF-1是野生脊椎动物生长条件与生长速率及身体体型变异之间的因果关联纽带。有趣的是，IGF-1水平的变化还在雏鸟中呈现出合理且清晰的、依赖于年龄与身体成熟度的适应性模式，以匹配其在生长投入中获得的收益，同时承担产后发育早期阶段的代价以最大化其进化适合度。因此，该机制可能是介导种群内生长速率遗传变异维持的机制之一，推测而言不受作用于生长速率的强定向选择存在与否的影响。