What Do Whales Taste?

Taste is so important that it's wheedled its way deep into our language. We call people we love 'sweetheart', and we hope they're not in a sour mood. When things go wrong, we may end up bitter about it. Tastes are a visceral part of our being. Like most mammals, we've evolved a sense of taste and the strong responses that go with it in order to guide us as we munch our way through the world. If you bite into something and it tastes sweet, it's probably good for you. Bitter things might be poisonous — probably a good idea to spit it out, or at least not to have too much. (Of course, the whole system evolved in a very different world than the one live in, so it easily goes wrong when faced with modern overabundance.) But what about the branch of mammals that went back to the sea — dolphins, whales, and porpoises. They spend their lives in a sea of brine, and everything they eat is permeated with it. What role does taste play in their life? Do they even taste their food?

A team of scientists tried to answer this question by amplifying the genes for taste receptors in a variety of cetaceans. Their study, which was published in BMC Evolutionary Biology, builds on earlier work which found that the genes encoding bitter, sweet and umami taste receptors were mutated and non-functional in dolphins. In this study, the researchers looked at the genomes of other cetaceans (around 10 species of toothed and baleen whales) and checked for the salty and sour receptors, too. They managed to amplify most of the genes from most of their samples, but most them had accumulated mutations that stopped them from working. The only exception was the salty receptors, which were still in working order.

So does everything taste salty to our marine cousins? Maybe, but we're still not sure. All of their food is rich in salt, so they can't really use taste to guide their choices they way we do, which might be why they've lost the other receptors. But then why do they still have the salt receptors? If everything tastes the same, why taste at all? A couple of pieces of evidence suggest that they may have given up on the sense of taste, too. For one thing, the skin of their tongue has only a few taste buds, suggesting that taste isn't particularly important to them. They also gulp down their food without chewing, which limits how much taste you get from your food. They may have kept the salt receptors not for taste, but because the same genes are involved in sodium transport. In the kidneys and elsewhere, these genes are important for maintaining hydration — that is, controlling the body's water and ion balance — which is absolutely critical for animals that live in saltwater.

So our cetacean cousins may not taste anything at all, or everything may taste salty to them. We don't know for sure. At the moment, I'm struggling to imagine what a world without taste would be like. Would eating still be a pleasure, or would the only reward be the feeling of being full? In humans, taste and smell are closely intertwined, so I wonder if and how smell interacts with a poor sense of taste in dolphins and their kin. Our ancestors parted ways over 50 million years ago, and our way of living is so profoundly different that it's incredibly hard to get into their head...but that doesn't stop me from wanting to.

Ref
Zhu, K. et al. The loss of taste genes in cetaceans. BMC Evolutionary Biology 14:218. (2014) doi:10.1186/s12862-014-0218-8