Wednesday, May 27, 2015

Highly stressed marmots are less likely to survive hibernation

Another marmot paper is out!

Wey TW, Lin L*, Patton ML, and Blumstein DT. 2015. Stress hormone metabolites predict overwinter survival in yellow-bellied marmots. acta ethologica, 18:181-185. doi: 10.1007/s10211-014-0204-6.

This has been out online for a while at:
But it just got included in a final paginated print volume.

Here's a quick summary:
There’s quite a lot of information in scat, aka animal feces—yes, poop. One kind of data that can be extracted is how stressed out an animal is. Animal’s produce more stress hormones in response to stressors, stimuli which could range from the threat of a predator to exercise. These hormones are eventually broken down and passed out of the body sometime later in feces. A normal stress response helps animals respond to their environment, but chronic stress can have negative health effects. (Sound familiar? It applies to people, too, of course.) For yellow-bellied marmots, getting ready for hibernation is a huge deal, and in a recent study , we found that the marmots that with very high levels of stress hormone by-products in their feces were less likely to survive the winter. This was true independent of their body weight, but the effect was bigger for skinner marmots, which suggests that being skinny and stressed out is an especially bad combination.

Read on for a more detailed description of the work...
Chronic stress can have negative health effects in humans and other animals, and methods to measure stress and its health impacts in wildlife are necessary for research and management. In particular, we want to find non-invasive measures that cause as little harm and stress to animals as possible. Glucocorticoid metabolites (the by-products of stress hormones) excreted in feces reflect the amount of stress hormones produced, and by proxy, the amount of stress response that animal had. Collecting feces is easy and, importantly, does not require drawing blood or other procedures that cause further stress to the animals. Measuring stress this way is, thus, a promising tool for wildlife studies, and in several species, higher levels of these fecal glucocorticoid metabolites (FGMs) are linked with reduced survival in populations of wild animals. (But, in other species, there is no evidence for this link.)

Yellow-bellied marmots require a lot of energy to hibernate successfully and survive the winter, and a previous study (Smith et al. 2012) confirmed that stressful stimuli resulted in higher levels of FGMs. Therefore, we hypothesized that marmots with the highest levels of FGM levels might be chronically stressed and the most likely to die during winter hibernation. We found that high FGM levels, both those measured over a long time (several months) or only in a short time (two weeks) right before hibernation, predicted lower chances of surviving the winter, as we expected. We also found that FGM levels were a stronger predictor of survival in skinnier marmots. This supports the idea that marmots with high levels of stress hormones are more likely to die during hibernation and that a combination of higher stress and low body weight is especially bad. Measuring stress hormone by-products this way therefore seems like one useful indicator of potential poor health in marmots, and our study adds to a more general understanding of the links between stress and health in wild animals.

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