Repeated exposure to stressful conditions can have beneficial effects on survival

Abstract

Repeated exposure to stressful circumstances is generally thought to be associated with increased pathology and reduced longevity. However, growing lines of evidence suggest that the effects of environmental stressors on survival and longevity depend on a multitude of factors and, under some circumstances, might be positive rather than negative. Here, using the zebra finch (Taeniopygia guttata), we show that repeated exposure to stressful conditions (i.e. unpredictable food availability), which induced no changes in body mass, was associated with a decrease in mortality rate and an increase in the age of death. As expected, the treated birds responded to the unpredictable food supply by increasing baseline glucocorticoid stress hormone secretion and there were no signs of habituation of this hormonal response to the treatment across time. Importantly, and consistent with previous literature, the magnitude of hormone increase induced by the treatment was significant, but relatively mild, since the baseline glucocorticoid concentrations in the treated birds were substantially lower than the peak levels that occur during an acute stress response in this species. Taken together, these data demonstrate that protracted exposure to relatively mild stressful circumstances can have beneficial lifespan effects.Key-words. Chronic stress, unpredictable food availability, glucocorticoids, corticosterone, HPA axis, hormesis. IntroductionProtracted or repeated exposure to stressful stimuli, such as those experienced by individuals living in uncontrollable or highly unstable environments, can have wide ranging effects on animal physiology, but the extent to which these effects are adaptive is the subject of considerate debate (Broonstra 2013). In vertebrates, one of the main systems mediating responses to stressful environmental conditions is the Hypothalamic-Pituitary-Adrenal axis (HPA axis), which regulates both basal production and transient surges of circulating glucocorticoid stress hormones. Transient increases in circulating glucocorticoids are a highly conserved component of the vertebrate stress response and play a key role in initiating an array of metabolic changes intended to mobilise energy, including hepatic gluconeogenesis and inhibition of glucose uptake by peripheral tissues . These changes are thought to be vital for promoting short-term survival (Wingfield et al. 1998;Sapolsky 2000). At the same time, dynamic changes in basal level of glucocorticoids, such as those occurring across differing seasons within the same year in a variety of free-living vertebrate species, are also thought to be critical for survival (Romero 2002). Over a longer time scale, however, the repeated activation of the HPA axis may lead to a dysregulation and dysfunction of the stress axis (Sapolsky 2000).The predominant view is that repeated stress exposure, and the consequent prolonged elevation of glucocorticoid levels, is harmful since it can induce a large variety of downstream negative effects, including impairment of brai...

Environmental conditions can modulate the links among oxidative stress, age, and longevity

“…We have previously shown that the treatment had no significant overall effects on body mass, measured up to three years of age, confirming that the random withdrawal of food altered primarily the temporal predictability of resources rather than the daily overall food intake (full details in Marasco et al 2015). Importantly, our environmental manipulation induced changes in the exposure to glucocorticoid stress hormones.…”

“…Finkel and Holbrook, 2000); 2) that the birds exposed to the challenging environmental protocol would show reduced oxidative damage given our previous finding of their improved survival (Marasco et al 2015), and 3) that individuals showing higher levels of oxidative damage would have shorter lifespans irrespective of the treatment.…”

“…We used captive zebra finches (Taeniopygia guttata) as our study species. We manipulated the quality of the environment by exposing experimental birds to unpredictable episodes of food withdrawal throughout adulthood (see full details in Marasco et al 2015). In this species, we have previously reported that such challenging environment moderately increased baseline levels of glucocorticoid stress hormone without overall affecting body mass (Marasco et al 2015), leading more surprisingly to improved probability of survival to the age of at least three years (Marasco et al 2015).…”

“…We manipulated the quality of the environment by exposing experimental birds to unpredictable episodes of food withdrawal throughout adulthood (see full details in Marasco et al 2015). In this species, we have previously reported that such challenging environment moderately increased baseline levels of glucocorticoid stress hormone without overall affecting body mass (Marasco et al 2015), leading more surprisingly to improved probability of survival to the age of at least three years (Marasco et al 2015). In this paper, we examine four different markers of oxidative stress in a randomly chosen subset of birds from the experimental population used in Marasco et al (2015): a DNA damage product (8-hydroxy-2'-deoxyguanosine, 8-OHdG), oxidative damage to protein (protein carbonyls), non-enzymatic antioxidant capacity (OXY), and superoxide dismutase (SOD) enzymatic antioxidant activity at two age points (early-and mid-adulthood).…”

Honest Signaling and Oxidative Stress: The Special Case of Avian Acoustic Communication

“…Unpredictable food availability during development resulted in reduced song output, shorter song bouts, and reduced repertoire sizes of adults (Spencer et al, 2004). An unpredictable food supply has also been shown to activate the hypothalamus-pituitaryadrenal (HPA) axis that releases glucocorticoids hormones (Fokidis et al, 2012;Marasco et al, 2015), which in turn can have pro-oxidant actions (Costantini et al, 2011a). For example, elevated plasma glucocorticoid concentrations increase the metabolic production of reactive molecule species, decrease the antioxidant protection, and disrupt the repair mechanisms of oxidative damage (Haussmann and Marchetto, 2010).…”