Penguins have lost 3 of the basic senses of taste
There are considered to be just 5 different tastes which many vertebrates can recognise, these being sweet, salty, bitter, sour and umami (or ‘meaty’). In humans, each taste bud contains between 50 and 100 cells which can decipher each of these flavours. Over the past 15 years, the explosion of molecular ecology has broadened our understanding of the genetic basis of many bodily functions including its links to taste and the areas encoding the recognition of different flavours. It has been found that, as one may expect, not all vertebrates share the same range of taste as humans but there are usually links within specific Orders of animals. For example, most birds cannot recognise sweet tastes, but can perceive bitter and umami flavours.
A recent population study conducted by the University of Michigan examined the genetic code of 5 penguin species – emperor, king, Adelie, chinstrap and rockhopper. This was conducted by specifically screening for the areas which code for the different types of taste; they were surprised to conclude that penguins have lost 3 of these basic tastes, with the responsible genes having ventured into the area of ‘psuedogenetics’, i.e. the gene (or an area resembling the gene) is there but is has lost its ability to form a protein. Penguins have therefore been left with only the ability to perceive salty and bitter flavours – surprising consider their diet is mainly fish. It has been noted however that as they swallow their food whole that this is less significant than if the another carnivorous mammal which does chew its food was lacking the receptors.
Penguins diverged from other tubenose seabirds around 60 million years ago; further divergence occurred around 23 million years ago to start to form the cluster of species that we recognise today. This 37 million year gap between these events is the time in which these taste buds are hypothesised to have been lost (rather than all independently losing the ability to taste more recently). As far as the current understanding goes, penguins are the only birds to possess only 2 types of taste receptors. The suggestion is that the frigid conditions in which the penguin live hamper the recognition of these flavours, that the proteins/receptors simply do not work. Further research is planned into the functioning of the Trpm5 protein which is necessary for the perception of sweet, savoury and umami flavours in all vertebrate systems so far studied.
These findings support an anatomical study of the penguin tongue dating back to 1998. It was suggested that penguins had a reduced perception of taste due to the lack of taste buds and the fact that they only had a single type of lingual papillae – a protrusion which holds the taste buds, of which humans have 4. The penguin papillae was hard and horn like (see above photo) – evolution appearing to have favoured the ability to maintain a grip on their slippery prey. Those involved in the study state that it is not clear whether the anatomical adaptions of the sensory changes came first.
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