Egg yolk carotenoids in relation to habitat and reproductive investment in the great tit Parus major.

Maternal allocation of antioxidants to egg yolk has been shown to affect early embryonic development and nestling survival. In environments with high levels of anthropogenic pollution, antioxidants (such as carotenoids) are important to protect the body from elevated oxidative stress. Thus, female allocation of antioxidants to yolk may be traded off against self-maintenance. Here we investigate maternal reproductive investment with respect to yolk carotenoid content and composition in relation to subsequent female condition and carotenoid status in urban and rural great tits Parus major. We found no differences between the urban and rural populations in total yolk carotenoids, egg mass, clutch size, hatching success, or female carotenoid status. Interestingly, however, rural eggs contained more zeaxanthin, a more potent antioxidant than lutein, which suggests that rural embryos have better antioxidant protection than urban embryos. Whether rural females actively transfer more zeaxanthin to the yolk or whether it passively reflects differences in dietary access or uptake needs to be further investigated. This highlights the importance of carotenoid identity and composition in future studies of carotenoid physiology, ecology, and signaling.