Varying intensities of chronic stress induce inconsistent responses in weight and plasma metabolites in house sparrows (Passer domesticus)

Abstract

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.

Neophobia, but not perch hopping, is sensitive to long‐term chronic stress intensity

“…Consequently, the most important comparisons of interest are across treatment groups. For example, immune function seems to exhibit more dramatic dysregulation in high‐stress individuals (Beattie, Rosen, et al, 2023), but the effects on plasma metabolites are inconsistent (Beattie, Fefferman, et al, 2023).…”

“…We conducted behavior tests on the captivity‐only group at the same timepoints as the medium‐stress group. The present study was part of a larger project in which blood samples were taken to measure other stress‐related metrics (Beattie, Fefferman, et al, 2023; Beattie, Rosen, et al, 2023) but behavior trials were never conducted at the same time as blood samples.…”

“…According to a computational model of reactive scope, one understudied aspect of chronic stress that may help elucidate this transition is the intensity and duration of the stress. The current experiments are part of a larger project that aimed to manipulate the intensity and duration of chronic stress to manipulate wear‐and‐tear, and thus the manifestation of chronic stress symptoms (Beattie, Fefferman, et al, 2023; Beattie, Rosen, et al, 2023). We predicted that higher intensity chronic stress would have more physiological and behavioral effects on an animal.…”

“…In the present study, we altered a pre‐existing method of inducing chronic stress (Rich & Romero, 2005) to create different intensity “levels” (Beattie, Fefferman, et al, 2023; Beattie, Rosen, et al, 2023) and monitored both neophobia and total activity (via perch hopping). If behavior is sensitive to the intensity of chronic stress, we would expect the most dramatic behavioral changes to be in higher intensity treatment groups.…”

Using point‐of‐care devices to examine covariation among blood nutritional‐physiological parameters and their relationships with poxvirus infection, habitat urbanization, and male plumage coloration in house finches (Haemorhous mexicanus)

“…For example, subclinical mastitis and Johne's disease in cattle can be rapidly and inexpensively screened on farms away from veterinary hospitals using POC devices (Kimura et al, 2012;Wadhwa et al, 2012). Many POC tests of nutritional physiology are now affordable and widely available, including real-time measurement of blood glucose, ketones, triglycerides, cholesterol, uric acid, and other components related to disease/health status (Beattie et al, 2023;DePinto & McGraw, 2022;Kim & Yoon, 2021;McGraw et al, 2020;McQuinn et al, 2020;Roy et al, 2022;Vitale et al, 2021) in humans and nonhuman animals (Srinivasan et al, 2017).…”