Saturday, October 25, 2014

Poor Whales, They Can Only Taste Salty

Two years ago I wrote an article about how carnivorous animals are oblivious to the taste of sweet things: tigers, lions, dolphins, sea lions, and your cat cannot differentiate between a bowl of sweet milk and a bowl of plain water.

But cetaceans, it seems, have lost more than just their sweet tooth.
Dolphins in the Ocean World Park, HongKong. Image: Malcolm Tang
Five basic types of taste exist: sour, sweet, bitter, salt, and umami. These five tastes can be distinguished by humans and are fundamental for physical and ecological adaptations in mammals. Umami and sweet tastes are attractive because they not only taste good, but are also essential to the ingestion of protein-rich and nutritious food. Salt, at low concentrations, is an attractive taste and is associated with sodium reabsorption and basic functioning of cells and neurons. Bitter tastes can cause taste aversion,thus protecting mammals from ingesting toxic substances. Sour tastes are unpleasant and can prevent the ingestion of unripe and decayed food resources.

Despite these adaptive benefits of taste some animals have lost the ability to taste one or more of the basic categories. Three types of vampire bats cannot taste umami and sweet. Chickens cannot taste sweet. And, as my previous post suggests, many meat-eating animals cannot taste sweet.
Sweet? What sweet? Image: Malcolm Tang
What about whales?
A group of scientists from Nanjing Normal University and Harvard Medical Center scanned the genomes for genes related to taste in 12 whale species and found only the genes for salty receptors. In layman's term it means cetaceans can only taste salty.

But why?
Firstly, there are no chocolates in the sea.
Secondly, even if there were chocolates in the sea, they would probably be salty.

Okay that wasn't serious. Now the serious part.

Both toothed and baleen whales swallow food whole with chewing. These behaviours reduce their dependence on taste in the search for food. Besides, when living in the oceans everything would just taste salty. Like seriously, have you ever tasted sea water? The saltines could make your failed cooking taste like heaven. And it would swamp out all the other flavors so it doesn't matter how sweet your chocolate may be, it will still tastes salty to that dolphin.
Dolphins in the Ocean World Park, HongKong. Image: Malcolm Tang
Anatomical evidence also reveals that both toothed and baleen whales have degenerated tongue epithelia and only few taste buds.

Why, then, do they retain the salty receptors?

Like all other animals, cetaceans need to regulate the balance of water and ion concentrations in their bodies. The balance is vital for cellular processes like transporting across the cellular membrane, and having salt receptors is vital in reabsorption of salt. Living in a salty environment means the osmotic pressure of their marine environment is higher than the vascular osmotic pressure in their bodies. A slight increase in salt concentration in sea water could disrupt the balance, causing the whales to excrete extra salt through urine, feces and milk, and that means extra work for their kidneys.

So remember, don't ever feed chocolates to dolphins.
They can't appreciate your sweet effort.


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