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.