Food restriction delays breeding and affects insulin-like growth factor-1, oxidative damage, and haematocrit value before egg-laying in female canaries

Environmental challenges, such as fluctuations in food availability, could influence reproductive investment. If resource availability is poor, individuals need to decide in which life-history process they invest more energy and vital compounds, which determine the cost of reproduction. In resource allocation, the physiological pathways have important roles. The aim of our study was to examine whether food availability influenced physiological traits (insulin-like growth factor-1 (IGF-1) concentration, antioxidant capacity (OXY), level of oxidative damage (ROM) and haematocrit value) prior to egg-laying in female canaries (Serinus canaria). We also tested whether these physiological traits were associated with traits reflecting the reproductive investment in egg macro- (egg mass and yolk mass) and micronutrient content (eggshell biliverdin- and protoporphyrin-based colouration). To test these questions we conducted a food restriction experiment with control and food-restricted (72% of control food) groups. Our study showed that food-restricted canary females delayed egg-laying and the physiological traits differed between the groups. At the pre-laying period, after 9-11 days of treatment, a reduction in plasma IGF-1 concentration, ROM level, and haematocrit value was detected in the control group, whereas in the food-restricted group plasma IGF-1 concentration increased, while ROM level and haematocrit value did not change. Plasma level of OXY was not influenced by treatment or breeding period. Plasma concentration of IGF-1, haematocrit value and oxidative status before egg laying did not affect the egg characteristics. Our study highlights the importance of breeding stage when studying and interpreting the effects of food restriction on physiological traits of breeding birds. Moreover, our data suggest that nutritional limitation had an effect on the timing of egg-laying that could be mediated by changes in physiological variables.

食物可获得性波动等环境胁迫，可能影响繁殖投入。当资源可获得性匮乏时，个体需权衡将更多能量与关键化合物投入到何种生活史进程中——而这正是繁殖成本的决定因素。生理通路在资源分配过程中发挥关键作用。本研究旨在探究食物可获得性是否会影响产卵前雌性金丝雀（Serinus canaria）的生理性状，包括血浆胰岛素样生长因子-1（insulin-like growth factor-1, IGF-1）浓度、抗氧化能力（antioxidant capacity, OXY）、氧化损伤水平（oxidative damage, ROM）以及红细胞比容值。此外，本研究还检验了这些生理性状是否与繁殖投入相关的卵宏观性状（卵重与卵黄重）及微量营养成分（卵壳基于胆绿素与原卟啉的着色特征）相关。为验证上述问题，我们设置了对照组与食物限制组（喂食量为对照组的72%）开展食物限制实验。研究结果显示，食物限制组的雌性金丝雀产卵延迟，且两组间的生理性状存在显著差异。在产卵前阶段，处理9-11天后，对照组的血浆IGF-1浓度、ROM水平与红细胞比容值均出现下降；而食物限制组的血浆IGF-1浓度反而升高，ROM水平与红细胞比容值则无显著变化。血浆OXY水平不受实验处理或繁殖阶段的影响。产卵前的血浆IGF-1浓度、红细胞比容值与氧化状态均未对卵的性状产生显著影响。本研究强调了在探究与解读食物限制对繁殖鸟类生理性状的影响时，繁殖阶段的重要性。此外，本研究数据表明，营养限制会影响产卵时间，而这一效应可能由生理变量的变化所介导。