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 onwa...动物的生活史（life history）与产后生长速率的变异紧密相关，因为个体在生命早期达成必要体质量的能力，直接关联其后续的存活与繁殖能力。令人意外的是，目前学界对连接食物可获得性与野生动物生长变异的生理机制仍知之甚少。 本研究对自由栖息的斑姬鹟（*Ficedula hypoleuca*）雏鸟开展了激素注射处理，旨在探究在产后发育早期，其血浆胰岛素样生长因子1（insulin-like growth factor 1，IGF-1）水平以及该因子对生长速率的介导效应，如何响应外源性IGF-1的施加。 研究结果显示，相较于对照组雏鸟，注射IGF-1的个体其血浆IGF-1水平、生长速率以及以体质量和跗跖长度（tarsus length）衡量的躯体尺寸均显著更高，且这些差异在雏鸟孵化后第7天起愈发显著……