Running has gotten very popular in the past few years. There was a time when jogger encounters were a relatively rare event on the streets but nowadays, it seems that anyone and everyone runs. I am often amazed at the crowd hitting the asphalt any time of the day, by any kind of weather.
As it got popular, jogging also became more high-tech. I live in a big city, and joggers with trendy, high-tech (and expensive) gear are common. However, as I was recently visiting a small country town, I was surprised to see two women jogging on a sidewalk, wearing the same kind of clothes and gear as those you would expect on marathon runners. It seemed to me to be the ultimate sign that running had really become the thing to do. (I’m not quite sure the kind of jogging-and-chatting these two women were doing, on a relatively mild spring weather day, really required the trendy high-tech gear they were wearing, but hey, whatever gets you off the couch and makes you enjoy your run, right?)
Now, why am I talking about jogging, and what is the scientific point of this post? Well, it’s nothing sensational. It’s just a small scientific study upon which I stumbled in the course of my morning reading, and that I wanted to share because it was cute and simple (yes, somehow cute). The bottom line of this study is that mice voluntarily choose to use a running wheel, even in the wild.
Wheel running is often used in research experiments as a way to stimulate and measure activity in mice. However, it has been claimed that it is not a “natural” behavior for mice, but rather one that develops only in captivity, and that could even perhaps be categorized as a pathological behavior. Noticing that there was no study that had actually investigated this issue and that there was therefore no proper data supporting the idea that wheel running was a behavior only occuring in captivity, two researchers from the University of Leiden asked a very simple question: if there is a wheel out in the wild, will free-living mice use it?
The answer is: yes, they will. The researchers placed running wheels in two different areas (a green urban area and a dune area not accessible to the public), and recorded the use of these wheels by mice (and other animals small enough to access the wheels) through motion sensors and cameras, over a period of three years. They found that mice did enter the wheels to run; these running bouts were longer than one minute in 20% of cases, the longest one lasting for 18 minutes. From the video recordings, the researchers noticed that the wheel running mice were mostly young ones. In the dune area, wheel running seemed to be more frequent during the night that during daytime, but in the green urban area, wheel running frequency was not significantly different between day and night, suggesting that light pollution in urban areas may affect the behavior of wild mice.
From this study, it appears that wheel running can be a voluntary behavior exhibited by wild mice in their natural environment. The question is then, what motivates mice to run in the wheel? Although this issue was not addressed in the study, the authors briefly touch upon possible mechanisms that involve reward and motivational systems. In an article in the New York Times covering this story, a scientist from the University of Michigan points out that running activates reward pathways in the brains of humans, but that there are also innate differences in temperament, in humans, but also in other animals. So, for every mouse that used the wheel, was there another one or perhaps several ones just sitting by and disdaining the exercise?
Finally, for the “cute” factor, check out the videos in the supplementary data section, you’ll see a mouse, a frog, and a slug using a running wheel.
Wheel running in the wild. Meijer JH and Robbers Y. Proceedings of the Royal Society B. 21 May 2014. doi: 10.1098/rspb.2014.0210
Meijer, J., & Robbers, Y. (2014). Wheel running in the wild Proceedings of the Royal Society B: Biological Sciences, 281 (1786), 20140210-20140210 DOI: 10.1098/rspb.2014.0210