Plasma Glutathione and Carotenoid Coloration as Potential Biomarkers of Environmental Stress in Great Tits

Abstract

Measures of oxidative stress in animals may be useful biomarkers of environmental stressors, such as anthropogenic pollution. In birds, studies of oxidative stress have focused on dietary antioxidants, primarily carotenoids, which are interesting due to their multiple physiological and pigmentary functions but therefore also unspecifically related to oxidative stress. A useful complementary biomarker may be the glutathione system, commonly used in human medicine, but rarely applied to wild, terrestrial vertebrates. In this study of urban versus rural adult and nestling great tits Parus major, we investigated both the carotenoid-based yellow plumage (by reflectance spectrometry) and the plasma levels of glutathione, the latter measured as total glutathione (tGSH) and as the ratio between oxidized and reduced glutathione (GSSG:GSH), respectively. We found that urban adults had higher current oxidative stress (GSSG:GSH) and paler yellow plumage compared to rural adults, suggesting elevated stress in the urban environment. Total glutathione levels (tGSH), however, which may indicate long-term up-regulation of the GSH reservoir, did not differ between the environments.Nestlings did not show any consistent pattern between environments in either tGSH or GSSG:GSH and, among individuals, glutathione levels were uncorrelated with carotenoid coloration. The results thus suggest some population-level correspondence between the two stress biomarkers in adult birds, but more work is obviously needed to understand how the two antioxidant systems interact in different individuals and in response to different environmental disturbances.

A multifactorial test of the effects of carotenoid access, food intake and parasite load on the production of ornamental feathers and bill coloration in American goldfinches

“…It has been proposed that birds like American goldfinches trade-off the use of carotenoid pigments for enhancement of the immune system versus for color display (Lozano, 1994;Moller et al, 1999;von Schantz et al, 1999). To date, all attempts to link feather coloration with oxidative stress have failed (Fitze et al, 2007;Isaksson et al, 2005;Navara and Hill, 2003). By contrast, several studies have shown that activating the immune system or inducing oxidative stress depresses bill coloration (Bertrand et al, 2006;Blount et al, 2003;Faivre et al, 2003;McGraw and Ardia, 2003;Perez et al, 2008).…”

Species-Dependent Effects of the Urban Environment on Fatty Acid Composition and Oxidative Stress in Birds

“…This has repeatedly been shown to result in changes in traits with potential fitness links, e.g., behavior, morphology, and reproductive investment (Gorissen et al, 2005;Isaksson et al, 2005;Fuller et al, 2007;Kempenaers et al, 2010). Likewise, several molecular and physiological parameters are also affected by the urban environment, including altered gene expression, endocrine changes, increased oxidative stress, and accelerated telomere attrition (Partecke et al, 2006;Isaksson, 2010;Atwell et al, 2012;Dominoni et al, 2013;Salmón et al, 2016;Watson et al, 2017).…”

Is oxidative status influenced by dietary carotenoid and physical activity after moult in the great tit (Parus major)?

“…Thus, coloration may be a reliable signal of physiological or immune condition. However, although many studies document the positive relationship between coloration and body condition or immune system, not all confirm these findings (Hõrak et al, 2004;Isaksson et al, 2005;Geens et al, 2009). Mechanisms underlying seasonal variation in coloration are not yet well understood, but some hypotheses have been advanced, such as UV bleaching, and bacterial or mechanical degradation (Delhey et al, 2010).…”