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.
