Rodents kept in captivity are often provided with wheels to encourage exercise and the animals, whether kept as pets or for laboratory testing, will often indulge in relatively long stints of running. Although wheel running is not exactly a natural scenario, people have often pondered over the reasons behind it. Now, a 3-year-long study published recently in Proceedings of the Royal Society B: Biological Sciences which set out to investigate this behavior in wild animals may finally have some answers.
Although it may not be something you consider from day to day as a pet owner, there has been a long standing debate over why rodents kept in captivity run on wheels. Animal rights activists have argued that it is a neurotic behavior which results from being kept in small enclosures. Some scientists, however, believe that the animals do it simply because they like to. It has been difficult to satisfactorily answer this question in the past because interpreting the behavior is tricky.
In order to shed light on the subject, a duo of neurophysiologists from Leiden University in the Netherlands set up an intriguing study that aimed to investigate wheel running in wild animals. The set-up was simple: they placed a running wheel in a garden and on a nearby grassy dune that was inaccessible to the general public. The wheel was placed within an enclosure in order to prevent larger animals from getting in and disrupting the experiment. They installed a motion-detecting infrared camera and scattered some tasty treats around, and waited for the action to come to them.
Over the next three years they captured some interesting footage. In total, over 200,000 recordings were made from animals visiting the site. They passed the footage onto trained observers in order to determine the species of the visitors. In addition to mice, a plethora of animals jumped on board the wheel and set it in motion including shrews, rats and frogs. The frogs didn't really run, though, rather they hopped from side to side which caused the wheel to rotate. A few slugs and snails even ventured into the wheel, but they were excluded because they caused haphazard movement as opposed to directional movement.
They found that the mice running on the wheel would typically go for 1 or 2 minutes, which roughly equated to the average amount that certain laboratory mice spend on wheels. One mouse even ran for a total of 18 minutes. They also observed some animals running on the wheel, leaving and then returning to run which suggested that the behavior was intentional.
In order to investigate whether the animals were only running in the wheel because food was around, lead author Johanna Meijer removed the food from the site and although the animals returned in smaller numbers, they still used the wheel. At times the animals would even wait around for others to finish, and one mouse sent another flying when it climbed into the wheel whilst it was occupied.
Taken together, these results seem to suggest that mice and other animals may exercise simply because they enjoy it, and that wheel running is a voluntary behavior at least for wild animals. According to Ted Garland, an evolutionary physiologist at the University of California, Riverside, who was not involved in the study, working out why some strains of mice are more sedentary than others may reveal genetic differences that could help explain why some humans are more active than others.