Chronic stress in free-living European starlings reduces corticosterone concentrations and reproductive success.
ABSTRACT Chronic increases in stress hormones such as glucocorticoids are maladaptive, yet studies demonstrating a causal relationship among chronic stress, increases in glucocorticoid concentrations, and subsequent fitness costs in free-living animals are lacking. We experimentally induced chronic psychological stress in female European starlings (Sturnus vulgaris) by subjecting half of the females at our study site to a chronic stress protocol consisting of 4, 30 min stressors (loud radio, predator calls, a novel object, or predator decoys including a snake, rat, and owl) administered in random order daily for 8 days after clutch completion. Experimental females were captured at the end of the chronic stress protocol (9 days after the onset of the chronic stress protocol), and unstressed control females were captured at the same stage of the nesting cycle. Chronically stressed females had lower baseline corticosterone (CORT, the avian glucocorticoid) concentrations and lower reproductive success than unstressed females. Furthermore, surviving nestlings in experimentally stressed broods showed sensitization of the CORT response to acute stress, which is a physiological change that could persist to adulthood. Attenuation of baseline CORT concentrations in adult females is contrary to the general assumption that elevated CORT concentrations indicate stress, suggesting that more research is necessary before CORT concentrations can be used to accurately assess chronic stress in field studies.
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ABSTRACT: During translocations, stress, as measured by the increase of glucocorticoids, cannot be avoided, but has been suspected to exacerbate the vulnerability to many causes of mortality after release. Therefore, measures to reduce stress have been proposed, such as keeping animals in pens before release (soft release). In this study, we investigated two open questions in translocations: (1) whether stress caused by the translocation procedure has an effect on survival; (2) whether soft release allows recovering from stress induced by capture and transportation. Hand-raised grey partridges showed a moderate adrenocortical response to transportation and kept the capacity to mount a stress response to a new acute stressor, partly by a decrease of corticosteroid-binding globulin capacity. In contrast to studies demonstrating a pervasive effect of capture and transport by virtual elimination of a proper stress response, we demonstrated a robust stress response and a return of baseline levels to pre-transport levels after 33 h of acclimatization. Possibly captive-bred birds may be less sensitive to capture and transportation than wild-caught birds. During the first month after release, birds held 33 h in release pens survived better when their corticosterone levels were lower. However, survival beyond the first month did not differ between birds held 9 or 33 h in acclimatization pens. Elevated glucocorticoids, as induced by the translocation procedure, likely affect short-term survival after release. We recommend glucocorticoid stress levels be surveyed in an appropriate subsample and minimized during translocations.Animal Conservation 07/2014; 18(1). DOI:10.1111/acv.12136 · 2.52 Impact Factor
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ABSTRACT: Whereas numerous studies have examined roads as anthropogenic stressors in birds and mammals, comparatively few studies have been undertaken on reptiles. We investigated plasma corticosterone (CORT) levels at baseline and following 30 min of restraint stress in free-ranging copperhead snakes (Agkistrodon contortrix) captured within the forest interior or while in contact with public roads. There was no difference in baseline CORT levels between snakes in the forest and on roads. Copperheads responded to restraint stress by increasing plasma levels of CORT; however snakes on roads exhibited a lower CORT stress response compared to forest snakes. Additionally, among snakes captured on roads there was a negative association between road traffic and baseline CORT, stressed CORT, and the magnitude of the CORT response. Our results suggest that roads are associated with a blunted stress response in copperheads. Reduced stress responses may be indicative of acclimation, the inhibited ability to mount a stress response in the face of prolonged chronic stress, or that road environments select for individuals with lower CORT responsiveness. Either scenario could result in increased road mortality if snakes do not perceive roads as a potential threat.General and Comparative Endocrinology 06/2014; DOI:10.1016/j.ygcen.2014.04.020 · 2.67 Impact Factor
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ABSTRACT: Recent emergence and spread of the amphibian fungal pathogen, Batrachochytrium dendrobatidis (Bd) has been attributed to a number of factors, including environmental stressors that increase host susceptibility to Bd. Physiological stress can increase circulating levels of the hormone, corticosterone, which can alter a host's physiology and affect its susceptibility to pathogens. We experimentally elevated whole-body levels of corticosterone in both larval and post-metamorphic amphibians, and subsequently tested their susceptibility to Bd. Larvae of three species were tested (Anaxyrus boreas, Rana cascadae, and Lithobates catesbeianus) and one species was tested after metamorphosis (R. cascadae). After exposure to Bd, we measured whole-body corticosterone, infection, mortality, growth, and development. We found that exposure to exogenous corticosterone had no effect on Bd infection in any species or at either life stage. Species varied in whole-body corticosterone levels and exposure to corticosterone reduced mass in A. boreas and R. cascadae larvae. Exposure to Bd did not affect mortality, but had a number of sublethal effects. Across species, larvae exposed to Bd had higher corticosterone levels than unexposed larvae, but the opposite pattern was found in post-metamorphic R. cascadae. Bd exposure also increased larval length in all species and increased mass in R. cascadae larvae. Our results indicate that caution is warranted in assuming a strong link between elevated levels of corticosterone and disease susceptibility in amphibians. The role of physiological stress in altering Bd prevalence in amphibian populations is likely much more complicated than can be explained by examining a single “stress” endpoint. J. Exp. Zool. 9999A: 1–11, 2014. © 2014 Wiley Periodicals, Inc.Journal of Experimental Zoology Part A Ecological Genetics and Physiology 06/2014; 321(5). DOI:10.1002/jez.1855 · 1.35 Impact Factor