Browsing by Author "Bauer, Carolyn M."

Now showing 1 - 5 of 5
  • No Thumbnail Available
    Item
    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.
  • Thumbnail Image
    Item
    Postnatal development of the degu (Octodon degus) endocrine stress response is affected by maternal care
    (2016) Bauer, Carolyn M.; Ebensperger Pesce, Luis Alberto; León, Cecilia; Ramírez Estrada, Juan Carlos; Hayes, Loren D.; Romero. L. Michael
  • No Thumbnail Available
    Item
    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.
  • No Thumbnail Available
    Item
    Social environment and anogenital distance length phenotype interact to explain testosterone levels in a communally rearing rodent: Part 1: The male side
    (2024) Correa, Loreto A.; Aspillaga-Cid, Antonia; Bauer, Carolyn M.; Silva-Alvarez, Danna; Leon, Cecilia; Ramirez-Estrada, Juan; Soto-Gamboa, Mauricio; Hayes, Loren D.; Ebensperger, Luis A.
    In vertebrates, male testosterone levels vary across the year being generally higher during the mating season relative to the offspring rearing season. However, male testosterone levels may also be associated with male anogenital distance (AGD) length (a proxy of prenatal androgen exposition), and influenced by the social group environment. In social species, it has been proposed that high levels of testosterone could be incompatible with the development of an amicable social environment. Thus, in these species, it is predicted that males have relatively low levels of testosterone. Our goal was to examine the potential association between male serum testosterone levels, season, male AGD length, and the social environment in the rodent Octodon degus under natural conditions. We quantified male serum testosterone levels during the mating and offspring rearing seasons, and we determined the number of females and males in each social group, as well as the composition of groups, in terms of the AGD length of the female and male group mates, from 2009 to 2019. Our results revealed that male testosterone levels covary with season, being highest during the offspring rearing season. Additionally, male testosterone levels vary with male AGD length, and female and male social group environments. More importantly, male degus exhibit low levels of testosterone that are indistinguishable from female levels during offspring rearing season. Similar to other highly social mammals, where males and females live together yearround, male amicable behavior could be the best male mating strategy, thus leading to a reduction in circulating testosterone levels.
  • No Thumbnail Available
    Item
    Social environment and anogenital distance length phenotype interact to explain testosterone levels in a communally rearing rodent: Part 2: The female side
    (2024) Correa, Loreto A.; Aspillaga-Cid, Antonia; Leon, Cecilia; Bauer, Carolyn M.; Ramirez-Estrada, Juan; Hayes, Loren D.; Soto-Gamboa, Mauricio; Ebensperger, Luis A.
    Testosterone is known as a "male" hormone; however, females also synthetize testosterone, which influences female sexual and aggressive behavior. In female vertebrates, as in males, testosterone levels can vary seasonally. However, female testosterone levels may also be related with female anogenital distance (AGD) length phenotype (a proxy of prenatal androgen exposure), and the social group environment. We used data from a long -term rodent study (2009-2019) in a natural population of degus (Octodon degus) to examine the potential associations between female serum testosterone levels, season, female AGD phenotype, and social group composition. We quantified female serum testosterone levels during the mating and offspring rearing seasons, and we determined the number of females and males in social groups, as well the composition of groups, in terms of the AGD of the female and male group mates. Our results indicate that female testosterone levels vary with season, being highest during the offspring rearing season. Additionally, female testosterone levels were associated with the number of male group-members and the AGD of male group-members but were not associated with female social environment and focal female AGD phenotype. Together, our results suggest that female testosterone levels are sensitive to intersexual interactions. Our results also reveal that female and male testosterone levels do not differ between the sexes, a finding previously reported only in rock hyraxes. We discuss how the complex social system of degus could be driving this physiological similarity between the sexes.