Physiological and behavioral responses of house sparrows to repeated stressors

Abstract

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.

House sparrows (Passer domesticus) adjusted hypothalamic‐pituitary‐adrenal axis negative feedback and perch hopping activities in response to a single repeated stimulus

“…This result for baseline Cort was not surprising. A closely related study that exposed birds to two different stimuli to initiate chronic stress also did not significantly alter baseline Cort in the initial 4 days (Gormally et al, ). This lack of change highlights that baseline Cort does not always change in a consistent manner in different species.…”

“…The experimental design was based on prior chronic stress studies that indicated that the hormonal effects of chronic stress are typically initiated within 8–12 days (Awerman & Romero, ; Cyr et al, ; DuRant, Arciniega, Bauer, & Romero, ; Gormally, Wright‐Lichter, Reed, & Romero, ; Lattin & Romero, ). In several of these studies, birds were exposed to different stressors at four different unpredictable times throughout the day for up to 3 weeks.…”

“…The novel objects included a plastic egg, a red food dish, and a ribbon clipped over the food dish. All three of these objects have been shown to elicit a neophobic response (Fischer, Franco, & Romero, ; Gormally et al, ). Each bird was exposed to all three objects, one each during the three sample periods (Control, Day 5, and Day 9; Figure ), with approximately a third of the birds exposed to each object at each sample period to control for any potential impact of presentation order.…”

Beyond corticosterone: The acute stress response increases DNA damage in house sparrows

“…Uric acid was measured using Amplex® Red Uric Acid/Uricase Assay Kits (Molecular Probes; Gormally, Estrada et al, 2019; Gormally, Wright‐Lichter, Reed, & Romero, 2018). Two‐hundred microliters of reaction buffer were used to dilute samples (2–3 μl plasma) and horseradish peroxidase and Amplex Red Reagent were added to convert uric acid to a red fluorescent product.…”

What are you actually measuring? A review of techniques that integrate the stress response on distinct time‐scales

“…Millet, Bennett, Lee, Hau, & Klasing, 2007), suggesting a response latency of about 1 hr (Figure 1). Bacterial killing capacity also can be affected by longer term stimuli, including habitat quality (Hopkins & DuRant, 2011), seasonal variation (Zimmerman, Paitz, Vogel, & Bowden, 2010), captivity (Love, Lovern, & DuRant, 2017) and repeated stressors (Gormally, Wright‐Lichter, Reed, & Romero, 2018; Table S1). Consequently, bacterial killing capacity can reflect stressor durations on the order of at least months, possibly even lifetime (Figure 1).…”