The effect of variation in dietary intake on maternal deposition of antioxidants in zebra finch eggs

1. Maternal diet can significantly influence the quality and size of eggs, and this may, in turn, influence the fitness of offspring. In this study, we show how antioxidants (vitamin E compounds and carotenoids) in the diet of female zebra finches influence the concentrations of antioxidants in their eggs. Antioxidants are biochemicals derived from the diet, which reduce damage to cell membranes caused by the free radicals produced during normal metabolism and growth. 2. Females were given either a seed-only or a seed + rearing food diet prior to egg laying. The seed + rearing food diet was more enriched with carotenoids, but had lower amounts of less effective antioxidants, such as gamma-tocopherol. Eggs were collected as they were laid, then analysed to determine the concentrations of antioxidants using high-performance liquid chromatography. 3. Females in the two food groups had similar rates of food consumption and laid similar sized clutches. Females on the seed-only diet produced eggs of similar mass to that of females on the seed + rearing food diet. 4. The concentrations of the most effective antioxidant (alpha-tocopherol) were higher in the eggs of females from the seed-only group and, for both food groups, concentrations decreased with successively laid eggs within clutches. The concentration of carotenoids in egg yolks did not differ between food treatments, but also decreased with successive eggs. Less effective antioxidants were relatively under-represented in eggs in relation to their availability in food, and were deposited in similar overall amounts between the two food treatments, and independently of laying sequence. 5. Our results indicate that egg size is not necessarily an accurate guide to egg quality, especially when comparing between clutches of different females or across species. Females may be able to adjust egg composition to influence offspring quality variation within broods, possibly traded-off against their personal use of antioxidants, their future reproductive success, control over sibling competition within their brood and/or brood reduction.