It’s a good thing that penguins don’t bother to waste time masticating when gobbling down all that raw fish, because it turns out they’ve got a pretty piteous palate anyway. According to new research, these famous waddlers have lost three of the five famous tastes that most of us vertebrates relish, leaving them only with salty and sour.
Interestingly, it seems that these losses occurred more than 20 million years ago. Although researchers can’t be sure of why it happened, they hypothesize it could be due to the fact that the receptors involved in picking up these other tastes don’t function in the frigid conditions that these aquatic birds dwell in, and thus they were kicked to the curb.
Tastes are simply sensations evoked by chemicals detected by cells in our taste buds. We tend to describe taste qualities using the five basic tastes: sweet, bitter, sour, salty and the recently introduced umami, the strong meaty or savory taste.
Alongside helping us enjoy our food, taste is actually crucial for survival in most animals. For example, bitter is thought to help prevent the ingestion of poisonous or toxic substances. But not all animals possess these five recognized tastes—almost all birds, for example, are missing the ability to discern sweet tastes, with the exception of the nectar-sipping hummingbird which converted its umami receptor into one that can pick up sweet. Scientists made this discovery not by measuring the gustatory function of birds, but by sequencing their DNA and looking for the genes responsible for detecting the different tastes in taste cells.
But it’s not just the sweet department that some birds seem to be lacking in; DNA analysis revealed that Adelie and emperor penguins seemed to be missing other taste genes, too. This sparked the interest of researchers at the University of Michigan, who decided to pursue it further.
For their study, which has been published in Current Biology, the team examined the genes present in these two penguins, alongside three other penguin species and 22 non-penguin birds. The researchers found that all of the penguins analyzed lacked functional genes for the taste bud receptors that pick up sweet, umami and bitter. This was particularly odd for a carnivore, given that umami gives the strong, meaty flavor. Conversely, all of the non-penguin birds contained functional genes for umami and bitter, but not sweet, which was expected.
So why is this? It could be that these tastes were not required, given penguins generally swallow their food whole, and thus were gradually lost. It’s possible that they retained the other two because sour helps them reject rotten food and salt helps them monitor their intake of this mineral. Alternatively, it may have something to do with the fact that the protein, Trpm5, required for picking up the three lost tastes doesn’t function well at lower temperatures. Since these genes basically became redundant, it’s likely that they gradually gained mutations over time and lost their function. And with evolution, if you don’t use it, you might lose it.
[Via Current Biology, University of Michigan, New Scientist and BBC News]