A group of researchers say they have established a new biomarker for how stressed polar bears are about climate change.
Last year, a team reported that fluctuations in climate and ice cover are closely related to stress among polar bears in East Greenland as indicated by levels of the stress hormone cortisol in hair samples. The team is hopeful this type of analysis will be beneficial once others learn that it can now be done with much greater reliability.
"Nobody else has done this so far," says Jerrold Meyer of the University of Massachusetts Amherst, who calls himself a behavioral endocrinologist. "We've not only been one of the key developers of the technique but we have also have worked very hard to demonstrate its reliability and validity. In collaboration with Melinda Novak, chair of the psychology department, we were among the first to show in a major controlled study that a prolonged or major life stress does lead to a demonstrable increase in cortisol in hair. Now we're making the technique available to others and we hope it spurs new collaborations with our lab."
Meyer says that over the past 40 years techniques have become not only much more sensitive and precise, but safer for researchers as they have been able to move away from using radioactive substances. "We can now measure much lower levels of substances than we could when I was a grad student," he recalls. "And with new enzyme immunoassay techniques read by a microplate reader, the work has become not only safer for researchers, but for lab workers and the environment."
To analyze cortisol levels in hair, the researchers need a sample about 3 cm long and weighing about 5 mg, that is, 10 or 12 strands. In humans, this amount cut from the scalp outward represents about three months of hormone activity as human hair grows an average 3 cm per month, Meyer notes. In his UMass Amherst lab about six undergraduates are currently learning the exacting techniques for washing and drying samples, grinding them to powder, extracting the cortisol, and conducting the enzyme immunoassay.
For the collaboration with Thea Bechshøft of Aarhus University and colleagues, Meyer's lab received blind hair samples from 88 polar bears legally killed between 1988 and 2009 in Greenland by indigenous people who have an arrangement with researchers to provide biological samples. Cortisol will persist in hair for hundreds of years, Meyer explains.
"We have analyzed this hormone in several blind samples of polar bear hair from museum specimens that were killed and stuffed in the late 1800s, and we had no trouble measuring it 125 years later," he says. "Others have measured cortisol concentrations in Peruvian mummies 1,500 years old. It's one of the beauties of hair cortisol, you can measure it in archival specimens."
Citation: Meyer, J., Novak, M., Hamel, A., Rosenberg, K. Extraction and Analysis of Cortisol from Human and Monkey Hair. J. Vis. Exp. (83), e50882, doi:10.3791/50882 (2014).