One aspect of the Reactive Scope Model is wear-and-tear, which describes a decrease in an animal’s ability to cope with a stressor, typically because of a period of chronic or repeated stressors. We investigated whether wear-and-tear due to chronic stress would accelerate a transition from phase II to phase III of fasting. We exposed house sparrows (Passer domesticus) to three weeks of daily fasts combined with daily intermittent repeated acute stressors to create chronic stress, followed by two weeks of daily fasts without stressors. We measured circulating glucose, β-hydroxybutyrate (a ketone), and uric acid in both fasted and fed states. We expected birds to be in phase II (high fat breakdown) in a fasted state, but if wear-and-tear accumulated sufficiently, we hypothesized a shift to phase III (high protein breakdown). Throughout the experiment, the birds exhibited elevated β-hydroxybutyrate when fasting but no changes in circulating uric acid, indicating that a transition to phase III did not occur. In both a fasted and fed state, the birds increased glucose mobilization throughout the experiment, suggesting wear-and-tear occurred, but was not sufficient to induce a shift to phase III. Additionally, the birds exhibited a significant decrease in weight, no change in corticosterone, and a transient decrease in neophobia with chronic stress. In conclusion, the birds appear
to have experienced wear-and-tear, but our protocol did not accelerate the transition from phase II to phase III of fasting.
more »
« less
House sparrows ( Passer domesticus ) adjusted hypothalamic‐pituitary‐adrenal axis negative feedback and perch hopping activities in response to a single repeated stimulus
Chronic stress has been extensively studied in both laboratory and field settings; however, a conclusive and consistent phenotype has not been reached. Several studies have reported attenuation of the hypothalamic–pituitary–adrenal axis during experiments intended to cause chronic stress. We sought to determine whether this attenuation could be indicative of habituation. Importantly, we were not investigating habituation to a specific stimulus—as many stress physiology studies do—but rather we assessed how the underlying physiology and behavior changed in response to repeated stressor presentation. We exposed house sparrows (
- Award ID(s):
- 1655269
- NSF-PAR ID:
- 10075785
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Experimental Zoology Part A: Ecological and Integrative Physiology
- Volume:
- 329
- Issue:
- 10
- ISSN:
- 2471-5638
- Page Range / eLocation ID:
- p. 597-605
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Despite decades of research, we still lack a complete understanding of what factors influence the transition of the necessary and adaptive acute stress response to what has become known as chronic stress. This gap in knowledge has illuminated the necessity for studies that examine the thresholds between these two sides of the stress response. Here, we determine how repeated exposure to acute stressors influences physiological and behavioral responses. In this repeated measures study, house sparrows ( Passer domesticus ) were exposed to a chronic stress protocol. We took physiological and behavioral measurements before, during, and after the protocol. Blood samples were used to assess four aspects of hypothalamic-pituitary-adrenal (HPA) axis function: baseline corticosterone, stress-induced corticosterone, negative feedback, and the maximal capacity to secrete corticosterone. We also assessed bacterial killing capacity and changes in uric acid concentration. Neophobia trials were used to assess behavioral changes throughout the protocol. We found no significant changes in HPA axis regulation in any of the four aspects we tested. However, we found that uric acid concentrations and neophobia significantly decreased after only four days of the chronic stress protocol, while bacterial killing capacity did not decrease until after eight days of exposure. These results indicate that different components of the stress response can be impacted by chronic stress on different timescales. Our results further indicate the importance of assessing multiple aspects of both physiology and behavior in order to understand how exposure to chronic stress may influence ability to cope with future challenges.more » « less
-
more » « less
One of the biggest unanswered questions in the field of stress physiology is whether variation in chronic stress intensity will produce proportional (a gradient or graded) physiological response. We were specifically interested in the timing of the entrance into homeostatic overload, or the start of chronic stress symptoms. To attempt to fill this knowledge gap we split 40 captive house sparrows (
Passer domesticus ) into four groups (high stress, medium stress, low stress, and a captivity-only control) and subjected them to six bouts of chronic stress over a 6-month period. We varied the number of stressors/day and the length of each individual bout with the goal of producing groups that would experience different magnitudes of wear-and-tear. To evaluate the impact of chronic stress, at the start and end of each stress bout we measured body weight and three plasma metabolites (glucose, ketones, and uric acid) in both a fasted and fed state. All metrics showed significant differences across treatment groups, with the high stress group most frequently showing the greatest changes. However, the changes did not produce a consistent profile that matched the different chronic stress intensities. We also took samples after a prolonged recovery period of 6 weeks after the chronic stressors ended. The only group difference that persisted after 6 weeks was weight—all differences across groups in metabolites recovered. The results indicate that common blood metabolites are sensitive to stressors and may show signs of wear-and-tear, but are not reliable indicators of the intensity of long-term chronic stress. Furthermore, regulatory mechanisms are robust enough to recover within 6 weeks post-stress. -
more » « less
Abstract To further elucidate the role that wear‐and‐tear plays in the transition from acute to chronic stress, we manipulated the intensity and duration of applied chronic stress to determine if behavior would respond proportionately. We brought wild house sparrows into captivity and subjected them to high‐stress, medium‐stress, low‐stress, or captivity‐only. We varied the number of stressors per day and the duration of stress periods to vary wear‐and‐tear, and thus the potential to exhibit chronic stress symptoms. The behaviors we assessed were neophobia (the fear of the new; assessed via food approach latency) and perch hopping (activity). We predicted that our birds would show proportionate decreases in neophobia and activity throughout a long‐term chronic stress paradigm. Our results indicate that neophobia is sensitive to the intensity of chronic stress, however, the birds became more neophobic, which was the opposite of what we expected. Conversely, perch hopping did not differ across treatment groups and is thus not sensitive to the intensity of chronic stress. Together, these data show that different behavioral measurements are impacted differently by chronic stress.
-
more » « less
Abstract Vertebrates respond to a diversity of stressors by rapidly elevating glucocorticoid (GC) levels. The changes in physiology and behavior triggered by this response can be crucial for surviving a variety of challenges. Yet the same process that is invaluable in coping with immediate threats can also impose substantial damage over time. In addition to the pathological effects of long-term exposure to stress hormones, even relatively brief elevations can impair the expression of a variety of behaviors and physiological processes central to fitness, including sexual behavior, parental behavior, and immune function. Therefore, the ability to rapidly and effectively terminate the short-term response to stress may be fundamental to surviving and reproducing in dynamic environments. Here we review the evidence that variation in the ability to terminate the stress response through negative feedback is an important component of stress coping capacity. We suggest that coping capacity may also be influenced by variation in the dynamic regulation of GCs—specifically, the ability to rapidly turn on and off the stress response. Most tests of the fitness effects of these traits to date have focused on organisms experiencing severe or prolonged stressors. Here we use data collected from a long-term study of tree swallows (Tachycineta bicolor) to test whether variation in negative feedback, or other measures of GC regulation, predict components of fitness in non-chronically stressed populations. We find relatively consistent, but generally weak relationships between different fitness components and the strength of negative feedback. Reproductive success was highest in individuals that both mounted a robust stress response and had strong negative feedback. We did not see consistent evidence of a relationship between negative feedback and adult or nestling survival: negative feedback was retained in the best supported models of nestling and adult survival, but in two of three survival-related analyses the intercept-only model received only slightly less support. Both negative feedback and stress-induced GC levels—but not baseline GCs—were individually repeatable. These measures of GC activity did not consistently covary across ages and life history stages, indicating that they are independently regulated. Overall, the patterns seen here are consistent with the predictions that negative feedback—and the dynamic regulation of GCs—are important components of stress coping capacity, but that the fitness benefits of having strong negative feedback during the reproductive period are likely to manifest primarily in individuals exposed to chronic or repeated stressors.
