8:59am

Tue March 13, 2012
The Salt

The Big Gulp: Dolphins Don't Have Time To Savor Their Food

Anyone who's visited an aquarium or watched "Flipper" reruns knows how happy those dolphins look when they score a nice fat fish. But they might not be tasting that fish at all.

That's the news from a study from researchers who tested the DNA of wild animals to see if they could taste sweet, bitter, and umami (or savory) flavor.

In earlier work they'd shown that tigers and house cats can't taste sweetness. Instead, they crave umami, the rich meaty flavor of steak, fish, and mushrooms. That might be a good thing in a cat, since they must eat meat to get the nutrients they need. (Here's our post on cats and their mushroom cravings, which sparked a slew of comments on the odd eating habits of cats.)

But the researchers were surprised to see that dolphins lacked the genes to detect not just sweet and umami, but bitter tastes, too. "One would think it would be useful in rejecting things," says Gary Beauchamp, director of the Monell Chemical Senses Center in Philadelphia, and an author of the study. It was published online in the Proceedings of the National Academy of Sciences.

Dolphins and other marine mammals might not have any taste receptors at all, Beauchamp speculates. "It may be that they're taste blind and they use vision, hearing, and tactile senses to detect food."

Since dolphins swallow their food whole, they're not missing out on the gustatory pleasures of gnawing on a nice bluefin tuna. But it's hard not to feel a wee bit sad at the notion of all those Sea World dolphins, unable to savor their post-performance reward.

Still, Beauchamp told The Salt, "Who's to know that we're not missing something they have?"

So maybe, just maybe, there's a mysterious seafood flavor that only dolphins can taste.

The researchers also looked at various carnivores to see if they had the genetic equipment to taste sweetness. Most of them, including the spotted hyena, the small-clawed Asian otter, and the fossa (a catlike creature that lives in Madagascar), didn't have the genes for sweet taste receptors, either.

Beauchamp said he was surprised how few carnivorous mammals have taste receptors. But he thinks that it's probably just a fact of evolution. As the animals became more carnivorous, the need to identify sweet carbohydrate tastes mattered less. Individual animals born without the ability to taste sweetness could survive and reproduce.

Sea lions also can't taste sweetness or umami, the study found. That makes sense, since they also swallow their seafood whole, like the dolphin. But there's one marine mammal that eats differently: the manatee. This vegetarian might have retained the sweetness genes, Beauchamp thinks, because sweetness is useful when foraging for plants.

"It will be real interesting when someone sequences [the genes of] the manatee," he said.

So stay tuned for news on the gustatory pleasures of the gentle manatee.

Copyright 2012 National Public Radio. To see more, visit http://www.npr.org/.