You wallow with pleasure in the stinking legacy: What lies behind the pandas’ strange predilection for horse manure, researchers have uncovered down to the molecular level. The animals only show this behavior at low temperatures. According to the studies, it is triggered by volatile substances in the excrement, which have an amazing effect: They influence the reactions of the temperature receptors and thus inhibit the sensation of cold. The pandas are apparently rolling around in the horse manure to avoid freezing, say the scientists.
Cute, charismatic and threatened: the giant panda (Ailuropoda melanoleuca) is the attraction of many zoos and a world-famous symbol of species protection. Its prominence has also made it a popular research subject. In the current case, however, it was a very curious behavior that a team of Chinese scientists devoted to. As Wenliang Zhou of the Chinese Academy of Sciences in Beijing and his colleagues report, there have been various indications that panda bears have a mysterious interest in horse manure: If possible, the animals wallow in piles, according to anecdotes. They have apparently had the opportunity to do so for a long time, because trade routes have led through the pandas’ range in central China for many centuries, the researchers write.
On the trail of strange behavior
As part of their study, they have now investigated the strange behavior extremely meticulously. First of all, by evaluating the recordings from video cameras, they examined the extent to which wild panda bears are actually interested in horse manure. They confirmed that males and females are attracted to the excrement, roll around in it and literally smear themselves with it. The evaluations of the data revealed a preference for relatively fresh, “fragrant” piles as well as a dependency on the ambient temperature: the animals only show this behavior in the winter months when the values are between -5 and 15 degrees Celsius.
The scientists then found out which substances in horse manure aroused the bears’ interest. As they report, they focused on two forms of the volatile substance beta-caryophyllene, which are typically found in manure. Experiments with panda bears in the Beijing zoo then showed that if you “scent” straw with these substances, the animals also begin to wallow in this material. The beta-caryophyllenes are actually the decisive substances.
Treatment against chills
But why could the animals be interested in them and why, of all things, at low temperatures? To investigate the question of whether the beta-caryophyllene has anything to do with the temperature sensation in mammals, the researchers carried out experiments with mice. They were able to show that test animals that had sniffed the substances were less sensitive to the cold. Accordingly, they were more willing to walk on a cold plate and, at four degrees Celsius, also showed less pronounced behavior that is normally associated with cold sensations.
It was therefore suspected that the beta-caryophyllene interacts with a molecular temperature sensor in the animals, thereby causing an increased cold tolerance. In order to check this specifically in the case of the pandas, the researchers used genome data: on the basis of genetic information, they produced thermal sensors for the bears in the laboratory. Using molecular biological investigations, they were then able to show that the beta-caryophyllene actually influence the function of these sensors: They therefore inhibit their activation by cold. In other words: the feeling of cold is suppressed.
Zhou and his colleagues now consider the curious riddle to be solved: Apparently, the beta-caryophyllene in horse manure gives the pandas relief from the unpleasant feeling of cold when the temperatures in their habitat drop to critical levels.