biology zoology blog taste tastebud

The Great Motivator Taste

Wasn’t it Columbus’ reason to discover America?

The sense of taste in humans, compared with that of other creatures, is poorly developed. For example, the threshold for tasting alcohol requires a 20,000 times greater concentration than that, which elicits a response in our olfactory receptors of the nose. Yet, we owe it to taste, not greed for gold or missionary zeal, that Columbus departed westward in search of a shorter route to the “Indies” and that Vasco da Gama a little earlier had successfully navigated around the tip of Southern Africa. European food in the Middle Ages must have been terribly bland and boring and to make it at least halfway palatable spices like nutmeg, cinnamon and cardamom, to name but three, were precious and needed from the Orient, from the “Indies”.

Taste is a chemical sense, in which the substance that is to be assessed has to be in contact with the receptor. While in fish taste receptors can occur at the tips of barbels and even fin rays, in higher vertebrates they are restricted to the mouth, where they are most numerous in the form of papillae on the tongue. Individual taste cells only survive for little more than a week and are then replaced by rapidly differentiating supporting cells from the papilla’s peripheral epithelial region. Because of this high turnover, taste cells themselves do not possess axons to send the information on the nature of the stimulus (e.g., sour, sweet, salty, bitter or umami, i.e. the taste of glutamate) to the brain. There are, however, nerve endings from permanent cells deeper in the tongue’s tissue, which contact the epithelial taste receptor cells and pick up the signal from them. Thus, we are in no danger of losing our sense of taste altogether, even if one set of replaceable taste cells has become damaged through physical injury, exposure to too great a heat, or too much “tabasco” and chilli pepper.

I have once examined taste receptor densities on the tongues of various species of fish and found that the smallest number of receptors occurred in deep-sea species, whereas the trout’s tongue, on the other hand, was extremely well endowed with them. In Antarctic fishes, the number of taste papillae was higher than in deep-sea species but less than what I measured in the trout. The explanation is simple: the trout in the river has an enormous spectrum of vertebrate and invertebrate food items to choose from (worms, tadpoles, insects, crustaceans, small fish, molluscs, kitchen wastes, etc), but for the deep-sea species in the lightless and impoverished oceanic abyss (disregarding biological light in the form of bioluminescence), the situation is very different. If you have hardly anything to eat, you simply cannot afford the luxury of being choosy; anything vaguely nutritious will be gobbled up. Under such conditions taste receptors would only complicate matters and possessing them (as well as good manners) would be a waste. To survive you need to fill your stomach with whatever comes along and is edible. And what about the Antarctic species? The food spectrum is not as varied as that for the trout, but at least during the Antarctic summer months food, largely consisting of different crustaceans and small fish, is plentiful and tasty – which is also what we Antarctic researchers found at our “gustatory analysis” of the Antarctic toothfish Dissostichus mawsoni. Just thinking of its superb taste seems to trigger my taste memory and a desire to savour it again one day.

© Dr V.B. Meyer-Rochow and, 2018.
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