Unearthing The Secrets Of Penguin Taste

This article is by Jenny Easley, a masters student in Exeter's Sensory Ecology and Evolution Group. She currently works on shore crab camouflage, but will soon be investigating taste perception in birds. Putting her marine skills and tasty knowledge into action, she writes about the wonders of the penguin palette.

The concept of having limited tasting abilities is one that is immensely difficult for us to grasp. Humans possess a highly advanced sense of taste, having 9,000 taste buds used by our ancestors to assess potential dangers when encountering novel food. Most humans today have no real use for taste anymore and don't use it for the reasons that have shaped its development. We need not worry that what we're having for dinner may be toxic to us, and many have access to food stamped with dates informing us of when something will become harmful to consume. Yet, for many species, assessing taste could be a matter of life and death. It is puzzling then, that some species have lost certain parts of their taste apparatus.

Vertebrate taste is categorised into five different flavours: sweet, sour, salty, bitter and umami (a savoury, meaty taste). Exciting new research from the University of Michigan has found that penguins are extremely lacking and in fact can only taste what is sour and salty! The absence of umami is perhaps especially peculiar given the main diet of the penguin is that of fish. So why has this happened?

Imagine the life of a penguin. A species brilliantly adapted for diving through the icy depths of the ocean, hunting fish. It is extremely unlikely you'd come across a tree laden with fruit, so why have the receptors to taste it? In fact, the loss of the sweet taste perception is not uncommon in the bird world, and certainly not unique to penguins, with studies showing the absence of T1R2 (the sweet receptor) is widespread throughout nearly all birds. The only exception to this is that of hummingbirds which detect sweet nectar using later evolved modifications to umami receptors^.

What is most surprising about these findings however, is the absence of other flavours. Take bitter taste for example, this is something that is enormously important to detect for many other avian species, helping them to avoid plants and animals defended with harmful toxins. Which bring us back to the previous point; could it be that the life history of the penguin does not warrant the need of the bitter taste gene? What is more important to them perhaps is being able to detect fish that are rotting and will cause them to be ill, and it has been suggested that this is the reason for the maintenance of the sour taste receptor.

An important message to take from this study is that all species live in very different sensory worlds, each adapted to their own niche. It is easy to assume that every living thing experiences things the same way we do and the realisation that they don't is astonishing.

So as you sit down to a meal today, step back and imagine how it would taste to a poor penguin!

References

Baldwin, Maude W., et al. (2014) Evolution of sweet taste perception in hummingbirds by transformation of the ancestral umami receptor. Science 345.6199, 929-933

Zhao, H., Li, J. and Zhang, J. (2015). Molecular evidence for the loss of three basic tastes in penguins. Current Biology, 25(4), R141-2

Images

1) The king penguin. Credit: Lieutenant Elizabeth Crapo via Wikimedia Commons.

2) An icy Antarctic scene. Credit Ben Holt via Wikimedia Commons.