While scientists were aware that both domestic and wild cats, which are carnivorous, have evolved without the ability to taste sweetness, researchers from the Monell Center were curious to see if they have maintained the ability to detect bitter tastes. After examining the DNA of domestic cats, they discovered that our feline friends have retained at least seven functional receptors that register bitter tastes, according to a news release. 

While it would have made a good story involving cats as the official "tasters" to suss out poison on the plates of royalty in the past, it turns out that these bitter taste receptors did not evolve to protect them from ingesting poisonous plants with bitter tastes.  Unlike sweet taste, which has only one or two different receptor types, the number of functional bitter taste receptor types varies greatly across species, the release explained. If bitter taste receptors evolved primarily to protect animals from eating toxic plants, then one could expect to find several functional bitter receptors in herbivores. However, since the researchers found that strictly carnivorous cats also had several bitter taste receptors, their study contradicts this long-standing belief. This suggests that cats are sensitive to bitter tastes, which may help explain why they are such picky eaters.

"Alternate physiological roles for bitter receptors may be an important driving force molding bitter receptor number and function. For example, recent Monell-related findings show that bitter receptors also are involved in protecting us against internal toxins, including bacteria related to respiratory diseases," Gary Beauchamp, author of the study and a behavioral biologist at Monell, said in a statement. 

Generally speaking, an animal's sense of taste helps it to distinguish nutritious foods from potentially harmful or toxic options. For instance, sweet foods such as fruit contain sugars that are an important source of energy. When animals eat these foods they associate them with being tasty and prefer to eat them over bitter tasting foods, such as are present in most poisonous plants. But carnivorous cats have evolved without the gene for sweet taste receptors since they have no need to detect sugars. This evolution is consistent with other carnivorous mammals, including sea lions and spotted hyenas.

"Cats are known as picky eaters," Peihua Jiang, leader of the study and a molecular biologist at Monell, said in a statement. "Now that we know that they can taste different bitters, our work may lead to better formulations of cat food that eliminate the bitter off-taste associated with certain flavors and nutrients."

For their study, Monell researchers examined DNA from domestic cats and identified 12 different cat genes for bitter receptors. Each of these receptors was tested to see if they were activated by one or more of the 25 different bitter-tasting chemicals. In doing so, researchers found that least seven of the 12 identified bitter receptor genes are functional. This means that they have the ability to detect at least one bitter chemical, according to the release. Although, further study is needed to determine if the additional five bitter receptors respond to other bitter compounds not used in this study.

Based on their results, researchers concluded that the number of bitter receptors an animal has is not directly related to the extent to which they do or do not consume plants. However, bitter taste could still act as a protective measure to make sure animals are not consuming toxic substances from the skin or other parts of certain prey species, including reptiles, amphibians and invertebrates. 

The findings were recently published in the journal PLOS ONE. 

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