Stress, Metabolism, and Antioxidants in Two Wild Passerine Bird Species

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The University of Chicago Press ABSTRACTAntioxidants protect against free-radical damage, and free radicals, in turn, are thought to underlie aging. Thus, measuring antioxidants may aid field ecologists in understanding the physiological mechanisms that underlie life-history trade-offs. Antioxidant levels are known to vary markedly in response to the stress of capture in many birds. These changes in antioxidants could result from regulation (e.g., by stress-related hormones) or consumption (e.g., by an increase in free radicals due to increased metabolic rate). Here we experimentally test the effect of increased metabolic rate on circulating antioxidant and corticosterone concentrations in two wild passerine bird species, house sparrows (Passer domesticus) and gray catbirds (Dumetella carolinensis). We increased metabolic rate via exposure to low ambient temperatures overnight in captivity and measured circulating antioxidant capacity, uric acid, corticosterone, and oxygen consumption in cold-exposed and control individuals. Both species showed increases rather than decreases in all antioxidant parameters overnight, contradicting a consumptionby-energy-expenditure hypothesis. Both positive and negative correlations between antioxidant response and corticosterone response were occasionally but not consistently present, refuting a generalized regulation-by-corticosterone hypothesis. High baseline uric acid predicted diminished response of corticosterone and all antioxidants. Thus, high uric acid may reflect recent stress, poor condition, or a compensatory response. Relationships among metabolic rate, antioxidants, and corticosterone differed qualitatively between the species.

Effects of immune supplementation and immune challenge on oxidative status and physiology in a model bird: implications for ecologists

“…Physiological parameters not only vary on ecological and evolutionary time scales (e.g. Tieleman et al, 2005;Lee, 2006;Cohen et al, 2008) but also can fluctuate and interact across very short time scales, as our study demonstrates, reflecting something similar to current 'health status' or 'physiological condition'.…”

“…For most parameters, this covariate was an important predictor of the LPS response strength. With antioxidants, baseline levels have been shown to predict response strength following an energetic challenge (Cohen et al, 2008), suggesting that physiological status affects the capacity to further increase antioxidant defences. Similarly, a ceiling may exist that limits further generation of antioxidants, even in the face of a pro-oxidant challenge.…”

“…We found a positive relationship between oxygen consumption and ROMs (Fig.2B). The majority of pro-oxidant radicals are by-products of respiration (Finkel and Holbrook, 2000), and their production is thought to be directly linked to the consumption of oxygen as a function of metabolism (Cohen et al, 2008). Higher metabolic activity and elevated oxygen consumption are therefore expected to correlate positively with the production of oxidants and with the demand for antioxidant defences.…”

“…Regarding physiological functions, confounding factors are likely to be numerous, diverse and interrelated. For example, indices of immune function and antioxidant capacity may vary with life history stage (Norris and Evans, 2000;Monaghan et al, 2009), age (Lavoie, 2005;Cohen et al, 2009a), stress levels (McEwen, 1998), energy use (Saino et al, 1998;Cohen et al, 2008), nutritional state (Cohen et al, 2009b) and health status (Costantini and Møller, 2009;Monaghan et al, 2009). By controlling for such confounding factors, studies that experimentally manipulate the physiological status of captive individuals living under standardized conditions are invaluable.…”

The role of the antioxidant system during intense endurance exercise: lessons from migrating birds

“…These molecules and enzymes work by preferentially oxidizing RS that would otherwise damage essential molecules in a cell. During migration, the circulating concentrations of endogenous antioxidants may be upregulated when RS production is high (Cohen et al, 2014;Jenni-Eiermann et al, 2014;Tsahar et al, 2006). We provide more information on components of the endogenous antioxidant system below.…”