Yolk Antioxidants and Mate Attractiveness in the Zebra Finch

1. Egg laying is costly for birds, as eggs must contain all the energy and nutrients needed by the developing embryo. As nutrients are limiting, there is a conflict between provisioning eggs and conserving nutrients for future health and survival. 2. Life-history theory suggests that females should choose how to invest resources in relation to the value of the reproductive attempt. Females may manipulate egg composition in relation to the attractiveness of their mate, ensuring chick survival and assuming that the offspring will themselves be more attractive and have higher reproductive success. Antioxidants are an important component of egg composition: they are vital for embryonic and posthatching chick development and survival. 3. Here we demonstrate that female Zebra Finches (Taeniopygia guttata) mated to attractive males deposit more carotenoids and alpha-tocopherol (vitamin E) in later-laid eggs, shown by a significant interaction between laying order and antioxidant concentration. This bias may increase the probability of chick survival from later-laid eggs and potentially the lifetime reproductive success of the laying female. 4. The body condition of the laying female, measured as fat reserves, was found to be a significant predictor of yolk carotenoid concentration but not of yolk alpha-tocopherol concentration.