Abstracts (first author)
Differential effects of pigmentary and non-pigmentary antioxidants on growth, plumage coloration and resistance to oxidative stress in wild great tits
Carotenoid-based colorations are thought to be honest signals of individual quality but the mechanism underlying their expression is still not clear. Since carotenoids act both as antioxidants and immunostimulants, it has been suggested that carotenoid-based coloration can signal an individual’s ability to resist oxidative stress and/or to mount an immune response. However, the antioxidant role of carotenoids in vivo has recently been debated. The "protection hypothesis" holds that carotenoids, which are minor antioxidants and are bleached by reactive oxygen species, can be used as signals to indicate the availability of non-pigmentary antioxidants (e.g. vitamins) that protect them from oxidation. Here, we evaluated this hypothesis by assessing the interactive effects of carotenoids and vitamins on plumage coloration, oxidative stress, growth and fledging success in nestling great tits. We supplemented nestlings with carotenoids (lutein and zeaxanthin) and/or vitamins (E and C) in a 2x2 full-factorial design, and subsequently measured plumage reflectance, antioxidant capacity, oxidative damage and body condition. Vitamins enhanced the expression of the carotenoid-based plumage coloration during the breeding season and improved antioxidant capacity. They did not influence oxidative damage, probably because supplied nestlings invested more in growth, which is a major cause of free-radical production, rather than in reducing oxidative damage. Moreover, vitamin-treated nestlings had a higher probability of fledging. In contrast, carotenoids did not influence any of these traits and did not show any synergistic effect when supplemented together with vitamins. Our results support the "protection hypothesis" and hence the idea that carotenoids are minor antioxidants in vivo. Furthermore, we could show the importance of antioxidants during growth, supporting the idea that oxidative stress may play a central role in life-history trade-offs.