The glucocorticoid stress response is frequently used to indicate vertebrate response to the environment. Body temperature may affect glucocorticoid concentrations, particularly in ectotherms. We conducted lab manipulations and field measurements to test the effects of body temperature on plasma corticosterone (predominant glucocorticoid in reptiles) in eastern fence lizards (
Baseline and stress-induced corticosterone levels across birds and reptiles do not reflect urbanization levels
Abstract Rates of human-induced environmental change continue increasing with human population size, potentially altering animal physiology and negatively affecting wildlife. Researchers often use glucocorticoid concentrations (hormones that can be associated with stressors) to gauge the impact of anthropogenic factors (e.g. urbanization, noise and light pollution). Yet, no general relationships between human-induced environmental change and glucocorticoids have emerged. Given the number of recent studies reporting baseline and stress-induced corticosterone (the primary glucocorticoid in birds and reptiles) concentrations worldwide, it is now possible to conduct large-scale comparative analyses to test for general associations between disturbance and baseline and stress-induced corticosterone across species. Additionally, we can control for factors that may influence context, such as life history stage, environmental conditions and urban adaptability of a species. Here, we take a phylogenetically informed approach and use data from HormoneBase to test if baseline and stress-induced corticosterone are valid indicators of exposure to human footprint index, human population density, anthropogenic noise and artificial light at night in birds and reptiles. Our results show a negative relationship between anthropogenic noise and baseline corticosterone for birds characterized as urban avoiders. While our results potentially indicate that urban avoiders are more sensitive to noise than other species, overall our study suggests that the relationship between human-induced environmental change and corticosterone varies across species and contexts; we found no general relationship between human impacts and baseline and stress-induced corticosterone in birds, nor baseline corticosterone in reptiles. Therefore, it should not be assumed that high or low levels of exposure to human-induced environmental change are associated with high or low corticosterone levels, respectively, or that closely related species, or even individuals, will respond similarly. Moving forward, measuring alternative physiological traits alongside reproductive success, health and survival may provide context to better understand the potential negative effects of human-induced environmental change.
more »
« less
- NSF-PAR ID:
- 10147637
- Date Published:
- Journal Name:
- Conservation Physiology
- Volume:
- 8
- Issue:
- 1
- ISSN:
- 2051-1434
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract Sceloporus undulatus ). First, we acclimated lizards to one of 4 treatments: 22 °C, 29 °C, 33 °C, or 36 °C, and measured cloacal temperatures and plasma corticosterone concentrations at baseline and after exposure to a standardized stressor (cloth bag). Both baseline and stress-induced corticosterone concentrations were lower in lizards with lower body temperatures. Second, we acclimated lizards to 22 °C or 29 °C and exposed them to a standardized (cloth bag) stressor for 3 to 41 min. Lizards acclimated to 29 °C showed a robust increase in plasma corticosterone concentrations with restraint stress, but those at 22 °C showed no such increases in corticosterone concentrations. Third, we measured lizards upon capture from the field. There was no correlation between body temperature and baseline plasma corticosterone in field-caught lizards. These results suggest body temperature can significantly affect plasma corticosterone concentrations in reptiles, which may be of particular concern for experiments conducted under laboratory conditions but may not translate to the field. -
The stress-induced susceptibility hypothesis, which predicts chronic stress weakens immune defences, was proposed to explain increasing infectious disease-related mass mortality and population declines. Previous work characterized wetland salinization as a chronic stressor to larval amphibian populations. Thus, we combined field observations with experimental exposures quantifying epidemiological parameters to test the role of salinity stress in the occurrence of ranavirus-associated mass mortality events. Despite ubiquitous pathogen presence (94%), populations exposed to salt runoff had slightly more frequent ranavirus related mass mortality events, more lethal infections, and 117-times greater pathogen environmental DNA. Experimental exposure to chronic elevated salinity (0.8–1.6 g l −1 Cl − ) reduced tolerance to infection, causing greater mortality at lower doses. We found a strong negative relationship between splenocyte proliferation and corticosterone in ranavirus-infected larvae at a moderate elevation of salinity, supporting glucocorticoid-medicated immunosuppression, but not at high salinity. Salinity alone reduced proliferation further at similar corticosterone levels and infection intensities. Finally, larvae raised in elevated salinity had 10 times more intense infections and shed five times as much virus with similar viral decay rates, suggesting increased transmission. Our findings illustrate how a small change in habitat quality leads to more lethal infections and potentially greater transmission efficiency, increasing the severity of ranavirus epidemics.more » « less
-
Invasive fish predators are an important factor causing amphibian declines and may have direct and indirect effects on amphibian survival. For example, early non-lethal exposure to these stressors may reduce survival in later life stages, especially in biphasic species. In amphibians, the glucocorticoid hormone corticosterone is released by the hypothalamo–pituitary–interrenal axis (HPI), as an adaptive physiological response to environmental stressors. The corticosterone response (baseline and response to acute stressors) is highly flexible and context dependent, and this variation can allow individuals to alter their phenotype and behavior with environmental changes, ultimately increasing survival. We sampled larvae of the spring salamander (Gyrinophilus porphyriticus) from two streams that each contained predatory brook trout (Slavelinus fontinalis) in the lower reaches and no predatory brook trout in the upper reaches. We measured baseline and stress-induced corticosterone release rates of larvae from the lower and upper reaches using a non-invasive water-borne hormone assay. We hypothesized that corticosterone release rates would differ between larvae from fish-present reaches and larvae from fish-free reaches. We found that baseline and stressor-induced corticosterone release rates were downregulated in larvae from reaches with fish predators. These results indicate that individuals from reaches with predatory trout are responding to fish predators by downregulating corticosterone while maintaining an active HPI axis. This may allow larvae more time to grow before metamorphosing, while also allowing them to physiologically respond to novel stressors. However, prolonged downregulation of corticosterone release rates can impact growth in post-metamorphic individuals.more » « less
-
more » « less
Abstract Glucocorticoids (corticosterone/cortisol; cort) are frequently used in conservation as biomarkers of disturbance in wild populations. However, the context‐dependent nature of cort means that it may not always accurately reflect disturbance. For example, there is growing evidence that wildlife populations can evolve or acclimate to human‐induced environmental change (i.e. contaminants) by expressing higher levels of tolerance. Mechanisms that allow for populations to achieve higher contaminant tolerance can be related to cort and thereby impact the reliability of cort as an indicator of disturbance. This study asks: (1) do wildlife populations that differ in tolerance to contaminants differentially express baseline and stress‐induced cort and (2) is cort a viable indicator of disturbance across populations that differ in tolerance to contaminants? Toward this goal, we identified three wood frog
Rana sylvatica populations with relatively high NaCl tolerance and three populations with relatively low NaCl tolerance. Tadpoles from these populations were reared to metamorphosis in either an environmentally relevant concentration of NaCl (0.5 g L−1NaCl) or a control (0 g L−1NaCl). At metamorphosis we used a non‐invasive waterborne assay to measure baseline and stress‐induced cort release rates and measured fitness‐related metrics. We found that contaminant tolerance influences cort levels. More tolerant populations had lower baseline cort and higher fitness compared to less tolerant populations. However, despite variation in cort across populations with different levels of tolerance, cort still represents a viable indicator of condition as our results show a consistent negative relationship between cort and fitness. Lastly, we found that levels of cort were consistent regardless of whether amphibians were reared in NaCl contaminated or non‐contaminated environments. Overall, we emphasize the importance of recognizing population‐level variation in cort due to contaminant tolerance when using cort as a biomarker for conservation purposes. -
Cooke, Steven (Ed.)Abstract Wild animals brought into captivity frequently experience chronic stress and typically need a period of time to adjust to the conditions of captivity (restraint, artificial lighting, altered diet, human presence, etc.), to which they may never fully acclimate. Changes in mass, the hypothalamic–pituitary–adrenal axis and heart rate parameters have been observed over the first week in newly captive house sparrows (Passer domesticus). In this study, we tested the effects of two drugs, diazepam and mitotane, in preventing the chronic stress symptoms caused by captivity, compared with oil-injected control animals. Diazepam is an anxiolytic that is widely prescribed in humans and other animals and has been shown in some cases to reduce physiological stress. Mitotane is an agent that causes chemical adrenalectomy, reducing the body’s capacity to produce glucocorticoid hormones. Our mitotane treatment did not cause the expected change in corticosterone concentrations. Baseline corticosterone was higher after a week in captivity regardless of the treatment group, while stress-induced corticosterone did not significantly increase above baseline after a week in captivity in any treatment group. However, mitotane treatment did have some physiological effects, as it reduced the resting heart rate and the duration of the heart rate response to a sudden noise. It also prevented the increase in nighttime activity that we observed in control animals. There was no effect of diazepam on corticosterone, resting heart rate, activity or heart rate response to a sudden noise, and no effect of either treatment on the sympathetic vs parasympathetic control of the resting heart rate. Together, these data suggest that mitotane, but not diazepam, can have a modest impact on helping house sparrows adapt to captive conditions. Easing the transition to captivity will likely make conservation efforts, such as initiating captive breeding programs, more successful.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/conphys/coz110
