6 research outputs found

    Causes and consequences of glucocorticoid variation in zebra finches

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    Dieren leven in een wereld van constante verandering, en glucocorticoïde hormonen (zoals corticosteron & cortisol) spelen een belangrijke rol in het reageren op voorspelbare en onvoorspelbare uitdagingen vanuit hun omgeving. Gezien glucocorticoïde hormoonconcentraties aanzienlijk toenemen na een onvoorspelbare uitdaging worden deze hormonen vaak beschouwd als ‘stress hormonen’. Individuen, soorten, en populaties laten, echter, grote variatie zien in hun glucocorticoïde concentraties en het interpreteren van de oorzaken en gevolgen van deze variatie is nog steeds een omstreden kwestie. In dit onderzoek gebruiken we zebravinken die leven in buitenvolières, waarin we de mate van omgevingsuitdagingen manipuleren tijdens hun ontwikkeling en tijdens hun volwassen leven. We onderzochten omgevings- (temperatuur, tegenslag tijdens de ontwikkeling & foerageerkosten) en interne (geslacht, gewicht & glucose regulatie) factoren die de glucocorticoïde variatie aansturen en hiernaast hebben we enkele fysiologische mechanismen onderzocht die betrokken zijn bij het glucocorticoïde systeem. We concluderen dat de belangrijkste oorzaak van glucocorticoïde variatie het metabolisme is, gezien we gevonden hebben dat glucocorticoïden gemoduleerd worden in overeenstemming met veranderingen in energieverbruik (zoals psychologische stressoren, temperatuursveranderingen & foerageerkosten), in zowel gecontroleerde binnenomstandigheden als meer natuurlijke buitenvolières. Dit roept de vraag op of glucocorticoïden indicators zijn van ‘stress’, los van het effect van stressoren op het metabolisme, gezien we gevonden hebben dat de fysiologische reactie op een verlaging van de temperatuur niet te onderscheiden valt van de reactie op een psychologische stressor, welke het metabolisme op eenzelfde manier verhoogde. Ons werk biedt nieuwe inzichten op de interpretatie van glucocorticoïde variatie en ligt ten grondslag aan de noodzaak om de traditionele interpratie van glucocorticoïden als ‘stress’ indicatoren en dierwelzijn te herzien

    Strong association between corticosterone levels and temperature-dependent metabolic rate in individual zebra finches

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    Glucocorticoid hormones (GCs) are often assumed to be indicators of stress. At the same time, one of their fundamental roles is to facilitate metabolic processes to accommodate changes in energetic demands. Although the metabolic function of GCs is thought to be ubiquitous across vertebrates, we are not aware of experiments which tested this directly, i.e. in which metabolic rate was manipulated and measured together with GCs. We therefore tested for a relationship between plasma corticosterone (CORT; ln transformed) andmetabolic rate (MR; measured using indirect calorimetry) in a between- and within-individual design in captive zebra finches (Taeniopygia guttata) of both sexes. In each individual, CORT and MR were measured at two different temperature levels: 'warm' (22 degrees C) and 'cold' (12 degrees C). CORT and MR were both increased in colder compared with warmer conditions within individuals, but also across individuals. At the between- individual level, we found a positive relationship between CORT and MR, with an accelerating slope towards higher MR and CORT values. In contrast, the within-individual changes in CORT and MR in response to colder conditions were linearly correlated between individuals. The CORT-MR relationship did not differ between the sexes. Our results illustrate the importance of including variation at different levels to better understand physiological modulation. Furthermore, our findings support the interpretation of CORT variation as an indicator of metabolic needs

    Glucose tolerance predicts survival in old zebra finches

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    The capacity to deal with external and internal challenges is thought to affect fitness, and the age-linked impairment of this capacity defines the ageing process. Using a recently developed intra-peritoneal glucose tolerance test (GTT), we tested for a link between the capacity to regulate glucose levels and survival in zebra finches. We also investigated for the effects of ambient factors, age, sex, and manipulated developmental and adult conditions (i.e. natal brood size and foraging cost, in a full factorial design) on glucose tolerance. Glucose tolerance was quantified using the incremental 'area under the curve' (AUC), with lower values indicating higher tolerance. Glucose tolerance predicted survival probability in old birds, above the median age, with individuals with higher glucose tolerance showing better survival than individuals with low or intermediate glucose tolerance. In young birds there was no association between glucose tolerance and survival. Experimentally induced adverse developmental conditions did not affect glucose tolerance, but low ambient temperature at sampling and hard foraging conditions during adulthood induced a fast return to baseline levels (i.e. high glucose tolerance). These findings can be interpreted as an efficient return to baseline glucose levels when energy requirements are high, with glucose presumably being used for energy metabolism or storage. Glucose tolerance was independent of sex. Our main finding that old birds with higher glucose tolerance had better survival supports the hypothesis that the capacity to efficiently cope with a physiological challenge predicts lifespan, at least in old birds

    Mural Endocarditis: The GAMES Registry Series and Review of the Literature

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