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What drives variation in the corticosterone stress response between subspecies? A common garden experiment of Swamp sparrows (Melospiza georgiana).

Smithsonian Migratory Bird Center, National Zoological Park, Washington, DC 20008, USA.
Journal of Evolutionary Biology (Impact Factor: 3.48). 03/2011; 24(6):1274-83. DOI: 10.1111/j.1420-9101.2011.02260.x
Source: PubMed

ABSTRACT Although differences in the corticosterone stress response have frequently been reported between populations or closely related subspecies, their origin remains unclear. These differences may appear because individuals adjust their corticosterone stress response to the environmental conditions they are experiencing. However, they may also result from selection that has favoured individuals with specific corticosterone stress response or from environmental factors that have affected the development of the corticosterone stress response during early life. We investigated these hypotheses by studying the corticosterone stress response of two closely related subspecies of swamp sparrows (Melospiza sp.). We showed for the first time that two closely related subspecies can differ in their corticosterone stress response when raised at the laboratory and held in similar conditions for a year. Thus, we demonstrated that selection, developmental processes or a conjunction of both of these processes can account for variation in the stress response between closely related subspecies.

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    • "In general, divergences in the adrenocortical activity between populations could appear because of: (i) physiological adjustments to the prevailing environmental conditions, (ii) differences in developmental processes, (iii) or different genetic backgrounds. Experiments conducted in common garden conditions can be useful to disentangle this assumption (Angelier et al., 2011; Dahl et al., 2012; Dunlap and Wingfield, 1995). Exploring the origin of population's differences in the HPG axis activity can broaden our notion about the adaptive nature of GCs release. "
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    ABSTRACT: Across vertebrates, the hypothalamic–pituitary–adrenal axis is a conserved neuroendocrine network that responds to changing environments and involves the release of glucocorticoids into the blood. Few stud- ies have been carried out concerning mammalian adrenal regulation in wild species either in the labora- tory or field, and even fewer have been able to determine true glucocorticoid baselines. We studied the South-American caviomorph rodent Octodon degus, a diurnal and social mammal that has become an important species in the biological research. First, we determined the plasma cortisol baseline and the acute stress concentrations during the non-reproductive and mating seasons in free-living individuals. Second, using the same protocol we assessed the impact of long-term captivity on the adrenal function in wild-caught degus and degus born in laboratory. Third, we examined laboratory groups formed with degus taken from two distant natural populations; one of them originally occurs at the Andes Mountains in high altitude conditions. The data revealed seasonal modulation of basal cortisol in the wild associated with mating. In laboratory, degus presented higher cortisol stress responses, with greater magnitudes shown in degus born and reared in captivity. No differences between populations were found. The results suggest differential regulatory mechanisms between basal and stress-induced cortisol levels, and context dependence of cortisol modulation in a mammalian species.
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    • "In general, divergences in the adrenocortical activity between populations could appear because of: (i) physiological adjustments to the prevailing environmental conditions, (ii) differences in developmental processes, (iii) or different genetic backgrounds. Experiments conducted in common garden conditions can be useful to disentangle this assumption (Angelier et al., 2011; Dahl et al., 2012; Dunlap and Wingfield, 1995). Exploring the origin of population's differences in the HPG axis activity can broaden our notion about the adaptive nature of GCs release. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Across vertebrates, the hypothalamic-pituitary-adrenal axis is a conserved neuroendocrine network that responds to changing environments and involves the release of glucocorticoids into the blood. Few studies have been carried out concerning mammalian adrenal regulation in wild species either in the laboratory or field, and even fewer have been able to determine true glucocorticoid baselines. We studied the South-American caviomorph rodent Octodon degus, a diurnal and social mammal that has become an important species in the biological research. First, we determined the plasma cortisol baseline and the acute stress concentrations during the non-reproductive and mating seasons in free-living individuals. Second, using the same protocol we assessed the impact of long-term captivity on the adrenal function in wild-caught degus and degus born in laboratory. Third, we examined laboratory groups formed with degus taken from two distant natural populations; one of them originally occurs at the Andes Mountains in high altitude conditions. The data revealed seasonal modulation of basal cortisol in the wild associated with mating. In laboratory, degus presented higher cortisol stress responses, with greater magnitudes shown in degus born and reared in captivity. No differences between populations were found. The results suggest differential regulatory mechanisms between basal and stress-induced cortisol levels, and context dependence of cortisol modulation in a mammalian species.
    General and Comparative Endocrinology 12/2013; 197. DOI:10.1016/j.ygcen.2013.12.007 · 2.67 Impact Factor
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    • "Comparing populations, CORT levels appear to be repeatable , to have a genetic basis, and thus to have the potential to evolve rapidly (Evans et al. 2006; Partecke et al. 2006; Rensel and Schoech 2011). CORT levels vary among subspecies that differ in their life-history (e.g., Angelier et al. 2011) and they have been associated with adaptation to urban environments (e.g., Partecke et al. 2006; Fokidis et al. 2009) and to ecotourism (e.g., Romero and Wikelski 2002). The research presented here is unique in simultaneously examining population divergence in both a behavioral trait and an associated hormonal mechanism, and in evaluating plasticity versus genetic evolution as possible causes. "
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    ABSTRACT: Novel or changing environments expose animals to diverse stressors that likely require coordinated hormonal and behavioral adaptations. Predicted adaptations to urban environments include attenuated physiological responses to stressors and bolder exploratory behaviors, but few studies to date have evaluated the impact of urban life on codivergence of these hormonal and behavioral traits in natural systems. Here, we demonstrate rapid adaptive shifts in both stress physiology and correlated boldness behaviors in a songbird, the dark-eyed junco, following its colonization of a novel urban environment. We compared elevation in corticosterone (CORT) in response to handling and flight initiation distances in birds from a recently established urban population in San Diego, California to birds from a nearby wildland population in the species' ancestral montane breeding range. We also measured CORT and exploratory behavior in birds raised from early life in a captive common garden study. We found persistent population differences for both reduced CORT responses and bolder exploratory behavior in birds from the colonist population, as well as significant negative covariation between maximum CORT and exploratory behavior. Although early developmental effects cannot be ruled out, these results suggest contemporary adaptive evolution of correlated hormonal and behavioral traits associated with colonization of an urban habitat.
    Behavioral Ecology 08/2012; 23(5):960-969. DOI:10.1093/beheco/ars059 · 3.16 Impact Factor
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