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Tree Shrews Love Hot Peppers Because They Don't Feel the Burn

One of the only traits left to distinguish us from other mammals is a tolerance—and in many cases deep, passionate love—for spicy foods. Richie Hertzberg at National Geographic reports that even that is under assault. A new study reveals that a species of Chinese tree shrew also seeks out hot peppers, and it's probably got a higher tolerance than you.

According to a press release, chili peppers do not grow naturally in the range of Chinese tree shrews, Tupaia belangeri chinensis, but they do feed heavily on Piper boehmeriaefolium, another species of plant that produces copious amounts of capsaicinoids, the compounds that give peppers their kick. Cara Giaimo at Atlas Obscura reports that researchers at the Kunming Institute of Zoology stumbled upon the shrew's tolerance while trying to figure out what the animals like to eat. The shrews, not true shrews at all but relatives of primates, are more genetically similar to humans than other lab animals like mice. So the institute houses about 2,000 of the 10-inch-long mammals for research. As they presented foods to the shrews, they were stunned to find the animals preferred hot peppers, something a self-respecting rabbit or macaque would never eat. (Some other animals, like birds, don't have capsaicinoid receptors, so they can munch peppers all they want.)

To understand the phenomenon, Chinese researchers collected five wild tree shrews and six wild mice to serve as controls. They fed the animals corn pellets spiked with capsaicin. Predictably, the shrews loved the spicy noms while the mice turned away. The researchers also collected bunches of Piper boehmeriaefolium from a local botanical garden. After synthesizing the capsaicin produced by the plant, they injected it into the animals. They then watched how often the animals licked the site, since licking is a response to pain, finding that mice licked the spot more often, a sign that they were irritated by the capsaicin. The shrews hardly licked the spots at all. After that they euthanized the animals to analyze their brains.

Unlike human pepper-heads, who enjoy the tingling on their lips, the slowly building heat and a rush of endorphins that comes from eating hot food, the shrews simply don't feel the burn much, if at all. That's because, the study in the journal PLoS Biology [open, DOI: 10.1371/journal.pbio.2004921] [DX] reveals, they have a mutation of the TRPV1 ion channel, also known as the capsaicin receptor. In other mammals, including the control mice, the receptor activates in the presence of capsaicin, causing pain and burning sensations.

Treeshrew.

Original Submission