Humans aren’t the only mammals with a sweet tooth. Omnivores from beagles to grizzlies can detect a wide range of flavors and enjoy the taste of sugar. But other mammals with narrow carnivorous diets have been subjected to evolution’s “use it or lose it” decree. These meat-eaters are genetic mutants without working taste receptors for sweets. Not only do they not want your cupcake, but they can’t even taste it.
Researchers led by Peihua Jiang at Monell Chemical Senses Center in Philadelphia wanted to know how often evolution has removed tastes from animals’ repertoires. Omnivores such as humans can detect five basic tastes: sweet, sour, bitter, salty, and umami (a meaty flavor). Previous studies had shown that cats, though, are indifferent to sweetness. Cats were also known to have a mutation in the gene for the sweet taste receptor, rendering it nonfunctional. Had other carnivores’ sweet receptors met the same fate?
For 12 carnivore species, the authors sequenced the genome section containing the sweet taste receptor. In just 5 of these species, the gene was intact. These included the aardwolf, Canadian otter, spectacled bear, raccoon, and red wolf.
It was presumably not practical to round up all these animals and give them tests to confirm that they like sugar. But the authors were able to test four spectacled bears, a charismatic South American species. When given a choice between a bowl of plain water and a bowl of sugar water, the bears strongly preferred the sugar water. They even enjoyed some artificial sweeteners (Splenda, for instance, but not NutraSweet).
The other 7 carnivore species in the study had mutations in their sweet taste receptors. These animals came from widely separated branches of the mammal family tree: sea lion and seals; Asian small-clawed otter; hyena; fossa (a cat-like creature from Madagascar); and banded linsang (a secretive jungle creature from Southeast Asia).
Though, again, the authors didn’t recruit any hyenas or jungle cats for their study, they did bring in two Asian small-clawed otters for testing. The otters were given the same bowls of sweetened and unsweetened water that the bears tasted. But the otters were totally indifferent to sugar water.
Finally, the researchers looked at the dolphin genome, which had been previously published. Not only was the dolphin’s sweet taste receptor mutated, but so was the receptor for umami flavor. There seemed to be no intact gene for a bitterness receptor, either.
It seems incredible that an animal could be so deficient in tasting. But previous studies have suggested that dolphins can’t taste sugar and have a reduced ability to taste bitterness. A close look at their tongues reveals only a few taste bud-like structures. The same is true of the sea lion: It has barely any taste buds, and has a mutated gene for the umami receptor as well as sweet.
They wouldn’t have much chance to taste their food even if they did have taste buds, though, because neither sea lions nor dolphins chew their prey. They both gulp down fish whole.
Jiang, P., Josue, J., Li, X., Glaser, D., Li, W., Brand, J., Margolskee, R., Reed, D., & Beauchamp, G. (2012). Major taste loss in carnivorous mammals Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1118360109
Note: This post was originally titled “Accounting for Taste: Why a Bear, but Not an Otter, Will Steal Your Cupcake.” But my attentive husband pointed out that there was a type of otter in the sugar-tasting group, as well as the sugar-ignoring one. I should admit now that I actually don’t know whether any of these animals steals pastries.