Female oxidative status, egg antioxidant protection and eggshell pigmentation: a supplemental feeding experiment in great tits

Oxidative stress has been suggested as a mechanism underlying the costs of reproduction and life history trade-offs. Reproductive activities may lead to high production of pro-oxidants, whose activity can generate oxidative damage when not countered by adequate antioxidant defenses. Because inter-individual differences in the efficiency of the antioxidant system are influenced by an individual's diet, food availability experienced during reproduction may affect the females' antioxidant status and, in birds, their ability to transfer antioxidants into their eggs. Moreover, a female's ability to cope with oxidative stress has been suggested to influence pigment deposition in the eggshell, suggesting a possible signaling function of eggshell maculation. Here we performed a food supplementation experiment in a natural population of great tits (Parus major) in order to investigate how nutritional conditions experienced during the egg laying period affect the female's oxidative status and egg investment and how maternal oxidative status and egg antioxidant protection relate to eggshell pigmentation. We show that food-supplemented females had lower oxidative damage levels (ROMs) than non-food-supplemented females. Furthermore, a female's ROMs levels were negatively associated with the levels of yolk antioxidant protection in her eggs, but this negative association was only significant in non-food-supplemented females. This suggests that oxidative stress experienced during reproduction influences the allocation of antioxidants into the eggs. Moreover, we observed a positive relationship between eggshell pigment distribution and maternal and yolk antioxidant protection, suggesting that eggshell pigmentation is a cue of female (and offspring) quality