In vertebrates, the Hypothalamic Pituitary Adrenal (HPA) Axis releases Glucocorticoids (GC) in response to unpredictable or uncontrollable stimuli, also known as stressors. The acute stress response shifts energy away from non-essential behaviors and directs it towards survival. Chronic stress or repeated exposure to acute stressors can result in chronically elevated levels of GC that can cause damage to the HPA axis, resulting in an inability to mount a stress response to new stimuli. It has been shown that long-term elevated GC levels can have serious negative impacts including inhibition of the reproductive system, suppression of the immune system, muscle wasting and protein loss, neuronal cell death, stunted growth, and inhibition of metamorphosis. 

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Measuring the levels of released GC can be used to determine the health of a population.  High baseline levels of GC have been linked to higher levels of infection and disease which can eventually result in population declines.  Anticipation of a stressor, such as the threat of predation, during specific life stages can act as chronic stressors. However, it is also possible that the threat of predation is predictable for specific life history stages and does not elicit a chronic stress response. 

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For my REU (Research Experience for Undergrads) project, I measured baseline and induced levels of Corticosterone, the main GC in amphibians, in the northern spring salamander to determine if the presence of predatory brook trout act as a chronic stressor. Adult Gyrinophilus in Hubbard Brook have declined in recent decades, which could be related to chronic stress. Detection of a change in GC excretion in response to a novel stressor is the best way to establish whether a population is chronically stressed.  Establishing baseline stress levels in a population can be useful for monitoring long-term population trends as well as identifying at-risk populations. 

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Institution: University of Montana

Lead Researcher: Maddy Cochrane

PI: Windsor Lowe