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.
"Livetrapping also has allowed the endocrine stress response to be linked to individual fitness and survival in many taxa (e.g., Wingfield et al. 1997; Cyr and Romero 2007), and long-term exposure to high levels of glucocorticoids (GCs) can correlate negatively with fitness (e.g., Sapolsky et al. 2000; Romero and Wikelski 2001, 2010). In addition, conservation biologists have begun using livetrapping to measure GCs in the field as an index of wild animal population health in response to human disruption and environmental change (Wingfield et al. 1997; Homan et al. 2003; Wingfield et al. 2011). "
[Show abstract][Hide abstract] ABSTRACT: While livetrapping is a vital field research tool, it is not a completely unbiased method of sampling. Biased trapping arises during field endocrinological studies whenever hormone levels or response influence the probability of capture of a subject. We repeatedly captured wild, free-living adult degus ( Octodon degus ) from the same location over 12 days to determine whether individuals with a certain endocrine stress profile were more likely to be captured repeatedly than others. We measured baseline cortisol (CORT), stress-induced CORT, and negative feedback efficacy via a dexamethasone suppression test in adult male and lactating and nonlactating female degus upon initial capture. We successfully recaptured approximately half of the degus. None of the 3 indices of the stress response at initial capture predicted whether a degu would be recaptured. However, baseline CORT levels at 1st capture had a weak, negative relationship with the number of days between 1st and 2nd capture. Because most animals interpret capture and restraint as an acute stressor, we also analyzed the effect of recapture on the endocrine stress response. Baseline and stress-induced CORT concentrations were measured upon each subsequent recapture for up to 5 total captures. Upon subsequent recaptures, neither stress-induced CORT nor baseline CORT changed significantly. Additionally, individual stress-induced and baseline CORT titers were repeatable within our sample population. These findings suggest that livetrapping does not select for animals with certain endocrine stress profiles, and that degus fail to habituate to repeated capture and restraint stress. Aunque la captura viva de animales ha sido fundamental en estudios de campo, el m e ´ todo de captura puede incluir algunos sesgos. En estudios conductuales y endocrinol o ´ gicos estos sesgos se producen cuando la probabilidad de captura de un individuo es afectada por su respuesta o por niveles hormonales. Se capturaron y recapturaron individuos silvestres del roedor Octodon degus durante 12 d i ´ as para determinar si los individuos con un perfil hormonal particular en respuesta a estr e ´ s por captura tienen una mayor probabilidad de ser capturados. Se examinaron tres componentes de la respuesta fisiol o ´ gica de estr e ´ s en degus hembras y machos: nivel basal de cortisol, nivel de cortisol inducido por estr e ´ s, y eficacia del sistema de retroalimentaci o ´ n negativa (a trav e ´ s de un ensayo con dexametazona). Durante el estudio se recapturaron cerca de la mitad de los individuos marcados originalmente. Ninguno de los tres componentes de la respuesta de estr e ´ s examinado fue capaz de predecir la probabilidad de recaptura en los degus examinados. Tampoco se detect o ´ una relaci o ´ n entre los niveles de cortisol medidos en la primera captura y el tiempo transcurrido hasta la primera recaptura. Tambi e ´ n se examin o ´ un posible efecto del n u ´ mero de recapturas sobre los niveles de cortisol basal y cortisol inducido por estr e ´ s. Aunque los niveles de cortisol inducido por estr e ´ s no cambiaron con el n u ´ mero de capturas, si se registr o ´ una disminuci o ´ n en los niveles basales de cortisol. Por u ´ ltimo, detectamos que los niveles de cortisol basal y cortisol inducido por estr e ´ s son repetibles en la poblaci o ´ n estudiada. En conjunto, los resultados indicaron que el trampeo reiterado no selecciona degus con perfiles hormonales particulares y que estos animales no muestran h a ´ bito al estr e ´ s producto de captura e inmovilizaci o ´ n reiteradas.
Journal of Mammalogy 08/2015; 96(4). DOI:10.1093/jmammal/gyv081 · 1.84 Impact Factor
"In songbirds, while a great deal of work has focused on the dynamics of sex-steroid availability to discrete neural circuits (see citations above), fewer studies have examined the nature of neural corticosterone (CORT) neurobiology and physiology. This is surprising, given the large amount of research devoted to understanding stress physiology, including the effects of chronic stress on CORT secretion (e.g., Cyr and Romero, 2007; Rich and Romero, 2005), behavioral effects of CORT (e.g., Breuner et al., 1998; Breuner and Wingfield, 2000; Busch et al., 2008; Loiseau et al., 2008; Pravosudov, 2003; Saldanha et al., 2000; Schoech et al., 2007, 2012; Spencer and Verhulst, 2007; Wada and Breuner, 2008), the role of developmental stress in the programming of the HPA axis (Crino et al., 2014; Schoech et al., 2011; Spencer et al., 2009), and the potential fitness consequences of glucocorticoid secretion over the lifespan of the individual (Bonier et al., 2009; Breuner et al., 2008; Brown et al., 2005; Cyr and Romero, 2007; Ouyang et al., http://dx.doi.org/10.1016/j.ygcen.2015.06.010 0016-6480/Ó 2015 Elsevier Inc. All rights reserved. "
"Indeed , through the perception of repeated negative events , also called stressors , chronic stress can disrupt homoeostasis and induce physiological and behavioural alterations ( Cyr and Romero , 2007 ) . These behavioural modifications might be the first way animals cope with environmental challenges ( Keeling and Jensen , 2009 ) . "
[Show abstract][Hide abstract] ABSTRACT: Animals perceiving repeated aversive events can become chronically stressed. Chronic activation of the hypothalamic-pituitary-adrenal (HPA) axis can have deleterious consequences on physiological parameters (e.g. BW, blood chemistry) and behaviour (e.g. emotional reactivity, stereotypies, cognition). Environmental enrichment (EE) can be a mean to reduce animal stress and to improve welfare. The aim of this study was first, to assess the effects of EE in battery cages on the behaviour of young Japanese quail and second, to evaluate the impact of EE on quail exposed to chronic stress. The experiment involved quail housed in EE cages and submitted or not to a chronic stress procedure (CSP) (EE cages, control quail: n=16, CSP quail: n=14) and quail housed in standard cages and exposed or not to the CSP (standard non-EE cages, control quail: n=12, CSP quail: n=16). Our procedure consisted of repeated aversive events (e.g. ventilators, delaying access to food, physical restraint, noise) presented two to five times per 24 h, randomly, for 15 days. During CSP, EE improved quail's welfare as their stereotypic pacing decreased and they rested more. CSP decreased exploration in all quail. After the end of CSP, quail presented increased emotional reactivity in emergence test. However, the effect of EE varied with test. Finally, chronic stress effects on comfort behaviours in the emergence test were alleviated by EE. These results indicate that EE can alleviate some aspects of behavioural alterations induced by CSP.
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