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Sunday, March 18, 2012

Carnivores can't detect sweetness

In order to be a successful carnivore, you need weapons to catch and devour your prey and a digestive system that can metabolize meat.  What you don’t need is a discriminating sense of taste.  Peihua Jiang and his colleagues at the Monell Chemical Senses Center sequenced the taste receptor genes of 12 carnivores and got some surprising results.

Mammals use specific receptors to detect different tastes.  We have at least five kinds of taste receptors for sweet, salt, bitter, sour and umami (meatiness or savoriness).  There is also now evidence of a sixth type of receptor that detects fat.  All mammals have remnants of the genes for these different receptors, but those genes aren’t necessarily functional. In particular, the obligate carnivores that were tested (animals such as cats that rely exclusively on a meat diet) had lost their sense of sweet taste. In contrast, the more omnivorous creatures (dogs and bears) retained their sense of sweetness.  This was tested both by looking for intact receptor genes and by offering the animals a choice between sweetened and unsweetened bowls of water. Interestingly, the different species tested had different errors in their receptor genes, indicating that they had independently lost the ability to taste sweetness.

This does make a certain amount of evolutionary sense.  An animal whose diet consists of living prey that can’t spoil or ripen has a limited need to detect how sweet its food is. On the other hand, animals that also eat plants can benefit from fully tasting their food.

This brings up an intriguing question.  If dogs have a better sense of taste than cats, then why are cats so picky while my dog will eat anything that hits the floor?

For more information on this study, check out Not Exactly Rocket Science.

A fossa, an obligate carnivore from Madagascar.