Penguins lost three of the five basic tastes – sweet, bitter and the savoury meaty taste known as umami – more than 20 million years ago, and have never regained them. This revealing came from a University of Michigan-led study of penguin genetics.
Penguins are basically fish eaters; the loss of the umami taste is especially perplexing. Although the findings are surprising and puzzling and cannot have a good explanation, the researchers have a few ideas. They suspects that the sensory changes are tied to ancient climate cooling events in Antarctica where penguins originated.
The leading hypothesis is that the genes were lost after cold Antarctic temperatures interfered with taste perception.
Vertebrates typically possess five basic tastes: Sweet, sour, salty, bitter and umami. Previous genetic studies showed that the sweet taste receptor gene is absent from the genomes of all birds examined to date.
For the study, the team took a closer look at the Adelie and emperor penguins data. In addition, they analysed bird tissue samples (chinstrap, rockhopper and king penguins, plus eight other closely related non-penguin bird species). They also reviewed publicly available genomes of 14 other non-penguin bird species. They found that all penguin species lack functional genes for the receptors of sweet, umami and bitter tastes.
The genomes of all non-penguin birds studied – including egrets, finches, flycatchers, parrots, macaws, falcons, chickens and mallards – contain the genes for the umami and bitter tastes but, as expected, lack receptors for the sweet taste.
Penguins originated in Antarctica after their separation from tubenose seabirds around 60 million years ago and the major penguin groups separated from one another about 23 million years ago.
The researchers are in the perception that the taste loss likely occurred during that 37-million-year span which included periods of dramatic climate cooling in Antarctica.