Taste Loss in Mammals
April 1, 2012 § Leave a comment
Scientists from the Monell Center reported online in Proceedings of the National Academy of Sciences USA that, due to the evolution of diet specialization, 12 related mammals of the sweet-blind species, which eats only meat, is losing its liking for sweet tastes.
The team’s previous study revealed that both domestic and wild cats are unable to taste sweet things because of a defect in the gene that manages the construction of the receptor for sweet tastes. This is odd since cats survive only on meat.
The Monell scientists next endeavored to solve whether other obligate carnivores have lost the sweet taste receptor. To do this they examined the sweet taste receptor genes of 12 related mammalian species with various dietary habits. The results confirmed a taste loss that is spread through many meat-eating species.
Gary Beauchamp, Ph.D., a behavioral biologist at Monell, senior author of the study said, “Sweet taste was thought to be nearly a universal trait in animals. That evolution has independently led to its loss in so many different species was quite unexpected.”
Veracity of the sweet taste receptor gene was directly linked to the animals’ diets. Species with the defective sweet receptor genes include sea lions, fur seals, Pacific harbor seals, Asian otters, spotted hyenas, fossas, and banded lingsangs, all species of which are exclusive meat eaters.
Those species found with the receptor genes in tact were the aardwolf, Canadian otter, spectacled bear, raccoon, and red wolf. These species are from both the obligate carnivorous and omnivorous diet groups.
Additional study disclosed that the defective portion of the sweet receptor gene is various among the seven species with defective receptors.
All of these findings suggest that the taste loss is diet-related, and that it has occurred repeatedly through an evolutionary series. This expresses the magnitude to which the structure and function of an animal’s sensory system is influenced by dietary niche.
The researchers wanted to further explore this finding. They wished to focus on the connection between feeding behavior and taste function. They examined the sweet and umami (savory) taste receptor genes in two mammals that have returned to the sea: the sea lion and the bottlenose dolphin. Both of these animals swallow their food whole, indicating that taste is not of high importance in their dietary range.
As the team had predicted, taste loss was present in these mammals. In both of them the sweet and umami receptor genes were not functional. The dolphin was also found to lack bitter taste receptor genes.
Beauchamp explains, “Different animals live in different sensory worlds and this particularly applies to their worlds of food. Our findings provide further evidence that what animals like to eat – and this includes humans – is dependent to a significant degree on their basic taste receptor biology.”
This research begs questions beyond diet choice because taste receptors are present in organs throughout the body, including the intestine, pancreas, nose, and lungs. These extra-oral taste receptors allegedly serve various functions.
Lead author and molecular biologist at Monell Peihua Jiang, Ph.D, says, “Our findings clearly show that the extra-oral taste receptors are not needed for survival in certain species. 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.”
“Extensive Taste Loss in Mammals”. (March 12, 2012). Neuroscience News. March 18, 2012. http://neurosciencenews.com/extensive-taste-loss-in-mammals/.