A penguin’s sense of taste appears to be limited to just sour and salt. Genetic research suggests that of the five vertebrate senses (sweet, umami, bitter, sour and salt), penguins only have taste receptors for sour and salt.
If you were to make a microscopic inspection of a penguin’s tongue, you’d find something fishy. “The lack of taste buds strongly suggests a reduction in taste function,” write the authors of a paper just out in Current Biology. This supposition is supported by their observation that Adelie and Emperor penguins (and by extension all other penguins) only have taste receptors responsive to sour and salt.
This is unusual. Whilst no bird yet studied can taste sweet, most are capable of perceiving umami and bitter notes (with the interesting exception of the red-throated loon, which would appear unable to do bitter). “Taken together, our results strongly suggest that the umami and bitter tastes were lost in the common ancestor of all penguins,” write Huabin Zhao and colleagues.
Why should this be? The authors offer a speculation. The taste receptors for sweet, umami and bitter are all sensitive to temperature, being less active in the cold. So even if they still had them, they wouldn’t be much use in sub-zero conditions in which the first penguins evolved.
