271 INTRODUCTION Aging refers to the age-related decline in biological functions ending up in decreased fitness features (Beckman and Ames, 1998; Kirkwood, 2002; Kregel and Zhang, 2007; Weinert and Timiras, 2003). According to the disposable-soma theory of the evolution of senescence, organisms have to face a decision about the optimal allocation of metabolic resources between self-maintenance and reproduction (Kirkwood, 1977; Kirkwood and Rose, 1991). When facing high levels of extrinsic mortality, the optimal resource allocation should be to invest fewer resources towards the maintenance of somatic structures than are required for an extended life span (e.g. Carranza et al., 2004). From a proximal point of view, aging is attributed to age-related changes that increase the risk of cellular death (Finkel and Holbrook, 2000; Harman, 1956; Harman, 1981). There is now accumulating evidence that age-related changes are due to oxidative damage (Finkel and Holbrook, 2000; Wickens, 2001). Oxygen and nitrogen reactive species (ROS and RNS) are unstable molecules that can damage proteins, lipids and DNA, finally compromising cellular function and integrity (Finkel and Holbrook, 2000; von Schantz et al., 1999; Wickens, 2001). To counteract the negative effect of ROS and RNS, aerobic organisms have evolved a variety of defence mechanisms, including enzymatic [superoxide dismutase (SOD), catalase (CAT) and peroxidases (GPX)] and non-enzymatic scavengers mostly acquired with food [carotenoids, vitamins E and C (Finkel and Holbrook, 2000; Harman, 1995; Wickens, 2001)]. Oxidative damage results from the unbalance between ROS/RNS production and the availability of antioxidant defences (Halliwell and Gutteridge, 2007). Age can alter both sides of this balance since aging has been associated with both an increase in ROS production and a weakened efficacy and/or availability of enzymatic antioxidants (Alonso-Alvarez et al., 2006; Beckman and Ames, 1998; Finkel and Holbrook, 2000; Torres and Velando, 2007; Wickens, 2001). Consequently, one might predict that senescent individuals should use more dietary antioxidants to counteract the increase in ROS/RNS production. However, the way that dietary ROS scavengers are allocated to the antioxidant function depending on individual age has been largely neglected in the evolutionary biology literature. This is surprising, given that some of the dietary antioxidants are also closely associated with other fitness-linked traits, such as the expression of secondary sexual signals. In recent years, carotenoids have been mastered as examples of compounds with pleiotropic effects. Carotenoids are indeed necessary for the development of yellow to red coloured ornaments, to stimulate the immune response, and have been shown to play a role as antioxidants (Alonso-Alvarez et al., 2004; Bendich, 1989; Blount et al., 2002; Horak et al., 2007; Pike et al., 2007). Nevertheless, it is important to keep in mind that the physiological properties of these pigments are currently under debate, since not all studies have provided support for the antioxidant function of carotenoids in vivo (Costantini and Moller, 2008; Hartley and Kennedy, 2004; Isaksson et al., 2007). For instance, Pike et al. (Pike et al., 2007) have shown that carotenoid-supplemented male sticklebacks (Gasterosteus aculeatus) have a more exuberant nuptial coloration, a better survival rate, a higher reproductive output, and, more importantly, a reduced level of oxidative stress compared with control individuals, whereas Costantini et al. (Costantini et al., 2007) did not report any effect of carotenoid supplementation on oxidative stress of nestling kestrels (Falco tinnunculus). It is not immediately clear why different studies have reported different results. Although, this is beyond the scope of the present article, it is possible that context-dependent effects (e.g. dose and duration of the supplementation, environmental conditions, additive/interactive effects with other antioxidants) might explain some of this variability. Since carotenoids cannot be synthesized de novo by animals (Goodwin, 1984), their supposed multiple functions should create trade-offs in carotenoid-limited individuals between ornamental The Journal of Experimental Biology 213, 271-277 Published by The Company of Biologists 2010 doi:10.1242/jeb.035188 Age-dependent allocation of carotenoids to coloration versus antioxidant defences J. Cote 1,2, *, E. Arnoux 1 , G. Sorci 1 , M. Gaillard 1 and B. Faivre 1 1 Biogéosciences UMR 5561, Université de Bourgogne, Dijon, France and 2 Department of Environmental Science and Policy, University of California, Davis, USA *Author for correspondence (jdcote@ucdavis.edu) SUMMARY Aging is commonly attributed to age-related changes in oxidative damage due to an increased production of reactive oxygen species (ROS) and a weakened efficacy of enzymatic antioxidants. These age-related changes might therefore modify the use of dietary antioxidants, including carotenoids. As carotenoids are closely associated with the expression of secondary sexual signals, the allocation of carotenoids to sexual signal versus antioxidant defences may vary with age. In this study, we explored how carotenoid-based ornament and antioxidant activity varied with age and how an inflammatory-induced oxidative burst affected ornament and antioxidant activity across a range of ages. Using zebra finches (Taeniopygia guttata) as a model species, we assessed circulating carotenoids, beak coloration and the plasma antioxidant status of birds of different ages before and after an inflammatory challenge. Our results show that old individuals display similar carotenoid-based sexual signals regardless of the availability of circulating carotenoids, suggesting a terminal investment of old individuals in their last reproductive event. Additionally, we found that an inflammatory insult induced a decrease in the total antioxidant activity and in the expression of a carotenoid-based sexual signal in the oldest individuals. These results suggest that old individuals pay an extra cost of immune activation possibly because the efficiency of antioxidant machinery varies with age. Key words: aging, honesty, signal, allocation strategies, zebra finches. THE฀JOURNAL฀OF฀EXPERIMENTAL฀BIOLOGY