Life Lines by Dr. Dolittle

Sponsored by the American Physiological Society

Staying warm on a chilly day

Photo of a wild giant panda after it rolled in horse manure. Image by F. WEI.

Giant panda bears have a very unusual trick to staying warm.

This unusual behavior was first noted by scientists at the Chinese Academy of Sciences in Beijing who observed a giant panda rolling around in horse manure in the Qinling mountains in central China during the winter of 2007. To see whether this was just a rogue panda or a more common behavior, scientists set up camera traps and observed 38 instances of pandas rolling around in manure. Now the scientists think they know why the animals have such an affinity for poop.

As it turns out, there are plant-derived chemicals (beta-caryophyllene (BCP) and beta-caryophyllene oxide (BCPO)) in fresh horse manure. In a recent paper, the scientists report only observing the pandas rolling in feces when the weather was cold (-5 to 5° C). Moreover, the animals only rolled in relatively fresh feces. To find out if the animals were attracted to these chemicals, they exposed captive giant pandas at the Beijing Zoo to hay that was scented either with the chemicals or with other chemicals. Consistent with their hypothesis, the animals spent more time with the hay that was coated in BCP/BCPO.

They next wanted to know whether BCP/BCPO could actually keep the animals warm by targeting cold receptors in their skin. To do this, they exposed the paw of laboratory mice to the chemicals and then measured their cold tolerance. Mice exposed to BCP/BCPO were not affected by cold whereas those exposed to saline shivered. The cold-sensitive receptor that BCP/BCPO targets was discovered to be the same one activated by menthol – TRPM8. Rather than activate the protein like menthol, BCP/BCPO inhibited the protein.

Personally, I prefer wearing a jacket. But, seeing as how giant pandas do not have access to clothing, I could see how this evolved.

In a quote by Dr. Elena Gracheva (neurobiologist at Yale University), this study “…shows the value in exploring behaviors out in the wild and looking for their molecular mechanisms.” But she also noted there could be other motivations for this behavior such as territorial defenses or anti-parasitic effects of feces.

References

W. Zhou et al. Why wild giant pandas frequently roll in horse manure. Proceedings of the National Academy of Sciences. Published online December 7, 2020. doi: 10.1073/pnas.2004640117

B.D. Charlton et al. Scent anointing in mammals: functional and motivational insights from giant pandasJournal of Mammology. Vol 101, April 8, 2020, p. 582. doi: 10.1093/jmammal/gyaa014

Science news

Categories: Comparative Physiology, Environment, Nature's Solutions

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