Environmental acidification is not associated with altered plasma corticosterone levels in the stream-side salamander, Desmognathus ochrophaeus.

As environments become increasingly altered due to anthropogenic factors, interest is growing in how endocrine systems respond to pollution and environmental degradation. Glucocorticoid hormones (GCs) are a type of stress hormones that are released upon activation of the hypothalamic-pituitary-adrenal axis and have widespread effects throughout the body. We tested the hypothesis that exposure to environmental acidification is associated with altered levels of plasma GCs in adult, stream-side Allegheny Mountain dusky salamanders (Desmognathus ochrophaeus). We compared plasma corticosterone (CORT) in salamanders living in 9 streams that differed in pH. Although capture and handling induced a robust increase in plasma CORT in all populations of salamanders, we discerned no significant effect of environmental pH on baseline CORT or handling-induced CORT levels. In a laboratory study, low pH decreased salamander locomotory activity compared to acid-neutral controls, but there was no effect of pH on plasma CORT. Decreased locomotory activity is a common amphibian response to stress, indicating that low pH has adverse effects on Allegheny Mountain dusky salamanders. Overall, we conclude that the effects of environmental pH on salamander behavior and other potential responses are not mediated by changes in plasma CORT levels. We discuss alternative explanations for our results and describe difficulties involved in searching for relationships between plasma GCs and environmental degradation.

Acute stressors increase plasma corticosterone and decrease locomotor activity in a terrestrial salamander (Desmognathus ochrophaeus).

Vertebrates respond to the onset of an acute stressor with an acute increase in plasma glucocorticoids. The increase in plasma glucocorticoids is believed to be adaptive, helping an animal cope until the stressful episode subsides. Although much is known about the effects of chronic elevation of glucocorticoids, far less is known about the role of acute increases in glucocorticoids in mediating stress responses. To better understand the regulation and function of acute increases in plasma glucocorticoids, we measured stress-induced increases in plasma corticosterone (CORT) and the effects of stressors and exogenous CORT on activity in male Allegheny dusky salamanders (Desmognathus ochrophaeus). Capture and handling of field-caught salamanders resulted in an acute elevation of plasma CORT during the nonmating season but not during the mating season. In laboratory-housed salamanders, a handling stressor that simulated capture resulted in decreased locomotor activity. Noninvasive elevation of plasma CORT via dermal patches did not replicate the handling-induced decrease in activity. Together, this work indicated that 1) the CORT response to the acute stressor of capture and handling was seasonally variable, 2) handling induced a decrease in locomotor activity in the laboratory, and 3) acute increases in plasma CORT did not contribute to stress-induced changes in locomotor activity. Future studies using noninvasive methods to elevate plasma CORT should illuminate the role of acute increases in plasma glucocorticoids in coordinating organismal responses to acute stressors.