Some sea otters can't taste sweet or unami flavours. Image: Shutterstock
Not all animals have a functioning sweet taste receptor.
Some mammalian species have lost their sense of sweet taste, according to scientists from the Monell Chemical Senses Centre in the US. Their findings suggest that likings for sweets may be lost during the evolution of diet specialisation, as each of the analysed species are exclusive meat-eaters.
A previous study revealed that both domestic and wild cats, which are obligate carnivores, are unable to taste sweet compounds due to defects in a gene that controls the structure of the sweet taste receptor. The researchers have now examined the sweet taste receptor genes from 12 related mammalian species with varying dietary habits.
Seven of the analysed species (sea lion, fur seal, Pacific harbor seal, Asian otter, spotted hyena, fossa and banded lingsang) have lost the sense of sweet taste. “Sweet taste was thought to be nearly a universal trait in animals,” behavioural biologist Gary Beauchamp said in a statement. “That evolution has independently led to its loss in so many different species was quite unexpected.”
The functionality of the sweet taste receptor gene appears to be closely related to the animals’ diets; the species with defective sweet receptor genes were exclusively meat-eaters. In contrast, the species with intact sweet receptor genes (aardwolf, Canadian otter, spectacled bear, raccoon and red wolf) were either exclusive meat-eaters or also ate other foods.
The researchers also examined sweet and umami taste receptor genes in the sea lion and bottlenose dolphin. Both species swallow their food whole, which suggests taste may not play such an important role in their dietary selection.
Both species have non-functional sweet and umami receptor genes. The dolphin also has non-functional bitter taste receptor genes.
Taste receptors have recently been identified in the intestine, pancreas, nose, lungs and other organs within the body, and scientists believe they serve many different functions. “Our findings clearly show that the extra-oral taste receptors are not needed for survival in certain species,” lead author Peihua Jiang said.
“The animals we examined did not have functional sweet, umami, or bitter taste receptors, so it will be important to identify how their functions were replaced throughout the body.”
