Stress in Salamanders: DU Biologist Finds It’s Not What You Might Think
What does it take to stress a salamander?
And what’s that four-legged creek dweller got to do with cubicle dwellers?
Biologist and researcher Dr. Sarah Woodley, associate professor in the Bayer School of Natural and Environmental Sciences at Duquesne University, is searching for answers.
Woodley, who has long studied salamanders of all sorts, currently is focusing on stress and immune system response in 3-inch long dusky salamanders, plain brown plethodontids that curious kids often unearth in neighborhood streams.
“If amphibians across the world are declining, how does stress play out?” Woodley asks. “Can we learn basic principles of physiology by looking at how stress affects amphibians?”
For three years, Woodley and some of her students have been looking at different types of environmental and biological stressors for salamanders, seeing how these impact the daily life of a salamander and its immune response. She’s found that possible stressors include:
- Acid mine drainage in streams.
- Higher salt content than in natural streams, reflected as Total Dissolved Solids (TDS) in water downstream of wastewater treatment plants and a byproduct associated with Marcellus Shale drilling.
- Predator cues. Since bigger species of salamanders eat smaller types of salamanders and their sense of smell is paramount, Woodley and her team expose the smaller salamanders to water that had been the home of their predators.
- Direct exposure to the stress hormone corticosterone, which is similar to the cortisol in humans that is implicated in depression, weight changes and bone thinning.
Woodley and her team revealed some interesting preliminary findings about their small, secretive subjects. Given the general reporting about human stress and its relationship to sickness and the immune system, they anticipated that stress could be a life changer for salamanders, too. What they found is sometimes yes, sometimes no.
According to Woodley, stress slows down salamanders. Their activity levels are one indicator of a stress reaction. So, if exposed to predator cues, acidic or salty water, they reduce their activity levels. This has serious consequences in the salamander world because they are hampered in foraging and forget to mate; they’re too busy conserving energy to do much else. Interestingly, they don’t exert the energy needed to leave the most intensely acidic and salty water, which could have relieved their stress.
Increasing stress levels don’t necessarily start a domino effect of physiological responses in salamanders. While their activity levels slow down in acidic water, the corticosterone levels don’t shoot up—and they don’t fall to amphibian pieces. “There could be other stress hormones or other stress mechanics at play,” Woodley theorized.
In other studies, Woodley directly tested the effects of stress hormones by using a dermal patch. The raised hormone level didn’t seem to impact daily salamander behavior or affect immune cells in the bloodstream. However, Woodley and her team noted one significant change: elevated corticosterone in the blood was accompanied by a decrease in body weight. It’s an interesting finding, given the human studies that show cortisol tends to help humans pack the pounds on, especially in the belly.
“It’s an additional piece of evidence that classic stress hormones function differently in salamanders,” Woodley said. “Based on work on other species, we expected decreased activity, eating and mating. Although other stressors have effects, corticosterone doesn’t seem to be at play.”
“In mammals, some stress hormones increase metabolism. In an amphibian with a low-energy lifestyle, perhaps levels of stress hormones are suppressed or uncoupled from stress responses to avoid metabolic costs,” Woodley explains. “Salamanders have the lowest metabolism of any vertebrae. Is this a survival mechanism in itself?”
So, Woodley and her team continue to piece together answers. “We can hope that by studying stress in this unusual species, we can better understand how it functions in human species,” she said.
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