Browsing by Author "Romero, L. Michael"

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    Habitat type influences endocrine stress response in the degu (Octodon degus)
    (2013) Bauer, Carolyn M.; Skaff, Nicholas K.; Bernard, Andrew B.; Trevino, Jessica M.; Ho, Jacqueline M.; Romero, L. Michael; Ebensperger, Luis A.; Hayes, Loren D.
    While many studies have examined whether the stress response differs between habitats, few studies have examined this within a single population. This study tested whether habitat differences, both within-populations and between-populations, relate to differences in the endocrine stress response in wild, free-living degus (Octodon degus). Baseline cortisol (CORT), stress-induced CORT, and negative feedback efficacy were measured in male and female degus from two sites and three habitats within one site during the mating/early gestation period. Higher quality cover and lower ectoparasite loads were associated with lower baseline CORT concentrations. In contrast, higher stress-induced CORT but stronger negative feedback efficacy were associated with areas containing higher quality forage. Stress-induced CORT and body mass were positively correlated in female but not male degus across all habitats. Female degus had significantly higher stress-induced CORT levels compared to males. Baseline CORT was not correlated with temperature at time of capture and only weakly correlated with rainfall. Results suggest that degus in habitats with good cover quality, low ectoparasite loads, and increased food availability have decreased endocrine stress responses. (C) 2013 Elsevier Inc. All rights reserved.
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    Seasonal variation in the degu (Octodon degus) endocrine stress response
    (2014) Bauer, Carolyn M.; Hayes, Loren D.; Ebensperger, Luis A.; Romero, L. Michael
    Many wild animals show seasonal variation in circulating levels of stress hormones. Seasonal changes in the stress response may help animals better cope with the different challenges faced during each life history stage. We determined the seasonal stress profile of wild, free-living degus in Chile. Female degus were sampled during non-breeding (January), mating/early gestation (July), late gestation (August), and lactation (1st litter-September, 2nd litter-January). Male degus were sampled during the first three time-points. We measured baseline cortisol (CORT), stress-induced CORT, and negative feedback efficacy using a dexamethasone suppression test. While we found that neither males nor females showed seasonal variation in baseline CORT or negative feedback levels, we did find significant seasonal variation in stress-induced CORT levels of both sexes. Male stress-induced CORT was lowest during mating while female stress-induced CORT was highest during late gestation and lactation. Overall, females had higher stress-induced CORT compared to males. Our data suggest that stress-induced levels of CORT are highest during periods with increased chance of stressor exposure or times of positive energy balance. Consequently, CORT responses to stress appear to be regulated according to different life history needs. (C) 2013 Elsevier Inc. All rights reserved.