Yolk carotenoids have sex-dependent effects on redox status and influence the resolution of growth trade-offs in yellow-legged gull chicks

Avian eggs are rich in carotenoids, which derive from maternal diet where they may be available in limiting amounts. Egg carotenoids may accomplish major roles in antioxidant protection or modulate physiological functions and growth, interfering with offspring redox status, potentially in a sex-dependent way. In this study of maternal effects in relation to sex and laying order of yellow-legged gull (Larus michahellis) chicks, we analyzed the consequences of increased yolk lutein concentration on plasma antioxidant capacity (AOC) and an index of early oxidative damage (reactive oxygen metabolites, ROM), till 9 days after hatching. To this end, for the first time we directly manipulated yolk lutein, thus avoiding any effect on other components of egg quality due to maternal supplementation before laying. Lutein did not increase AOC but increased ROM in males and in first-laid chicks. Hence, lutein did not act as an antioxidant and determined increased early oxidative damage, possibly because of upregulation of immune or other physiological functions, but these effects were sex-related and apparent in first-laid chicks with larger yolk lutein supply. ROM positively covaried with AOC, suggesting a trade-off between AOC and oxidative damage. Moreover, lutein injection altered the covariation between body size or immunity and AOC or ROM. Carotenoids may thus not be major antioxidants in birds and rather affect redox status by increasing oxidative damage in a sex-dependent way and interfere with the resolution of growth trade-offs. In the absence of sex-related allocation, maternal decisions on egg carotenoid concentration may depend on the balance between divergent effects on either sex