Expression of carotenoid-based trait in blackbirds Turdus merula increases with metal pollution level

Resumen del trabajo presentado al 23rd Annual Meeting of the Society of Environmental Toxicology and Chemistry, celebrado en Glasgow (Escocia) del 12 al 16 de mayo de 2013.-- et al.Carotenoid-based traits in vertebrates, and notably in birds, are considered as “honest signals” of their bearers’ genotypic and phenotypic quality, and thus ultimately of their survival ability and reproductive value. The expression of carotenoid-based ornaments has been widely studied, and is known to be affected by different environmental stressors. For instance, metal environmental pollution has been shown to fade the yellow plumage of the great tit Parus major, and it has been suggested that this is related more to depletion of carotenoid-rich food than to metal-induced oxidative stress. We tested the hypothesis that metal pollution affects the expression of a carotenoid-based trait in the European blackbird Turdus merula (a sexually dimorphic species in which males exhibit a yelloworange beak), and investigated whether this may be related to direct toxic effects impairing health and anti-oxidant status and/or to indirect effects related to diet. Fifty-five free-living males were captured during the breeding season along a pollution gradient in Antwerp (Belgium). They were aged (yearling versus older), beak reflectance spectra were measured, and blood and feather samples were collected. Body condition index, hematology, and plasma biochemistry were studied to assess health status. Preliminary analyses showed an increase of beak coloration with environmental metal pollution: carotenoid chroma increased and hue decreased (more orange beak) with pollution level. Brightness did not vary with pollution level. Some health parameters exhibited relationships (positive except for K) with carotenoid chroma (namely Ca, albumin and uric acid levels, and ALP activity in plasma) or hue (MCH and MCHC of blood, plasma K and Mg levels and ALT and AST activities), but according to age-specific patterns in most of cases. However none of the parameters studied as health indicators was found to differ according to pollution level, except plasma total protein levels in older birds only. Altogether, the results strongly suggest that the factors explaining the increase in beak coloration with pollution were not yet identified. Ongoing analyses on individual exposure (metals in feathers and blood), oxidative stress (blood antioxidant levels and lipid peroxidation) and diet (stable isotopes of C and N in blood and diet items) might allow revealing the mechanisms underlying such a beak color enhancement with metal environmental pollution.Peer Reviewe