Why Cats Can't Taste Sweet

[Aggie]

Short answer: They've a defective sweet receptor gene.

Long answer:
http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.0010003

Abstract

Although domestic cats (Felis silvestris catus) possess an otherwise functional sense of taste, they, unlike most mammals, do not prefer and may be unable to detect the sweetness of sugars. One possible explanation for this behavior is that cats lack the sensory system to taste sugars and therefore are indifferent to them. Drawing on work in mice, demonstrating that alleles of sweet-receptor genes predict low sugar intake, we examined the possibility that genes involved in the initial transduction of sweet perception might account for the indifference to sweet-tasting foods by cats. We characterized the sweet-receptor genes of domestic cats as well as those of other members of the Felidae family of obligate carnivores, tiger and cheetah. Because the mammalian sweet-taste receptor is formed by the dimerization of two proteins (T1R2 and T1R3; gene symbols Tas1r2 and Tas1r3), we identified and sequenced both genes in the cat by screening a feline genomic BAC library and by performing PCR with degenerate primers on cat genomic DNA. Gene expression was assessed by RT-PCR of taste tissue, in situ hybridization, and immunohistochemistry. The cat Tas1r3 gene shows high sequence similarity with functional Tas1r3 genes of other species. Message from Tas1r3 was detected by RT-PCR of taste tissue. In situ hybridization and immunohistochemical studies demonstrate that Tas1r3 is expressed, as expected, in taste buds. However, the cat Tas1r2 gene shows a 247-base pair microdeletion in exon 3 and stop codons in exons 4 and 6. There was no evidence of detectable mRNA from cat Tas1r2 by RT-PCR or in situ hybridization, and no evidence of protein expression by immunohistochemistry. Tas1r2 in tiger and cheetah and in six healthy adult domestic cats all show the similar deletion and stop codons. We conclude that cat Tas1r3 is an apparently functional and expressed receptor but that cat Tas1r2 is an unexpressed pseudogene. A functional sweet-taste receptor heteromer cannot form, and thus the cat lacks the receptor likely necessary for detection of sweet stimuli. This molecular change was very likely an important event in the evolution of the cat's carnivorous behavior.

Interesting paper. They speculate that perhaps the mutation caused Felidae to become super-carnivores due to their lack of attraction to sweet foods. Evolution is amazing... one genetic mess-up and all of a sudden: CATS!

There's a fluffy pink kitten, indeed. 

[Swatopluk]

And birds lack the receptors for capsaicin. So bird food can be protected from squirrels etc. by putting hot chili into it.
There is the theory that capsaicin producing plants evolved to have their seeds only be attractive to birds who would swallow them whole and deposit them far away with some guano fertilizer while other animals that would stay close and destroy the seeds by chewing and digestion would be repelled.

[Sibling Zono (anon1mat0)]

I'm not sure about that, many parrots are seed eaters, they process the kernels and their poop doesn't have any viable seed material, that applies to pigeons and many passerines too. It's possible that capsaicin has been out-evolved by birds or that the predators it defends against were never birds in the first place but fruit eaters (mammals).

[Opsa]

I'm not so sure about cats not being able to taste sweetness. I had a cat that went berzerk whenever we had chocolate doughnuts in the house, and would beg for them. Another cat was positively possessive about cantaloupe. Also- I've heard of cats  (and other animals) dying because they lapped up antifreeze, being attracted by it's sweet smell.

[Aggie]

I'm not sure about that, many parrots are seed eaters, they process the kernels and their poop doesn't have any viable seed material, that applies to pigeons and many passerines too. It's possible that capsaicin has been out-evolved by birds or that the predators it defends against were never birds in the first place but fruit eaters (mammals).

There's always a 'target audience' for seed dispersal, as well as the hoodlums that sneak in the back door. Fleshy fruits are meant to be eaten in most cases; a plant wouldn't be well-served to waste energy making fruits if they were simply meant to drop to the ground.  Better to have a wind-dispersed seed in that case. Some fruits are not particularly tasty, which can change the timing of dispersion (if they are a food of last resort in the winter, the seeds get dropped with a fertilizer load closer to spring).

It's possible that seed-eaters have exploited peppers as a food source, but that they originally evolved for different avian vectors (or that the local fauna didn't include many seed eaters when these evolved). I suppose it's also possible that peppers evolved for mammalian vectors who didn't chew their food, to avoid seed disturbance (I certainly notice them further down the digestive tract, but perhaps that's not universal).

[Bob in a quantum-state-of-faith]

I'm not so sure about cats not being able to taste sweetness. I had a cat that went berzerk whenever we had chocolate doughnuts in the house, and would beg for them. Another cat was positively possessive about cantaloupe. Also- I've heard of cats  (and other animals) dying because they lapped up antifreeze, being attracted by it's sweet smell.

Smell is different from taste, or so I seem to recall.



I'm always super-careful about antifreeze spills, as there's apt to be kitties/doggies about.   I dilute with water usually where it is dispersed into harmlessness down into the soil-- it biodegrades nicely enough.

[Aggie]

I'm always super-careful about antifreeze spills, as there's apt to be kitties/doggies about.   I dilute with water usually where it is dispersed into harmlessness down into the soil-- it biodegrades nicely enough.

Glycols are not super-toxic, but I'd not recommend this as a main method of disposal. All the little eukaryotic organisms in the soils may not take too kindly too it! It's probably safe enough if you are just washing down or diluting very small spills rather than getting rid of old or excess fluid. There should be depots (often auto dealers or parts stores) which will accept bulk quantities for recycling.

_{Certain chemicals are safe enough to dispose of, well diluted, down the sink, but that's only in cases where you are connected to sewer (not septic) and the city has a rigorous treatment process.  I'd not recommend it in general, though, and never for large quantities. NEVER put anything down a storm drain - those usually discharge to the nearest waterway, untreated.}

[Bob in a quantum-state-of-faith]

I was speaking of spills-- not removal and disposal.

Because no matter how many buckets you put underneath?  Some excess always manages to splash out onto the ground.   Back in the day, I'd pour it along the fence line, as a grass killer.  These days?  It's easy to get rid of at the local recycler's.

But after it's drained, I empty the old into the used bottle the new came in-- there's always room enough, due to the unavoidable spills.  And I also rinse off the engine, not wanting a sticky residue all over the place.

[Aggie]

 

[Swatopluk]

Chocolate is poison for dogs (I think it's the taurin). Don't know about cats.

[Bob in a quantum-state-of-faith]

Chocolate is poison for dogs (I think it's the taurin). Don't know about cats.

I'd heard it was the caffeine.... but I really have no idea.

[Sibling Zono (anon1mat0)]

It's the theobromine which is toxic for dogs, cats, rats and birds.

[Swatopluk]

It's the theobromine which is toxic for dogs, cats, rats and birds.

Yes, you're right. My mistake. Taurin(e) is a different matter.
I only knew about the effect on dogs but considered it likely that other animals (at least mammals) could react similarly.

[Griffin NoName]

My next door neigbour's poodle, when I was a child, always liked a bowl of tea (made in the usual way as a cup of tea) everyy day.

[Swatopluk]

Tea is far less problematic than coffee because the caffeine is slowed down and partially masked by tannin(s).

[pieces o nine]

Moufette was never one to pass up a nice, cold iced tea...



Dom prefers Earl Grey served hot.       

[Roland Deschain]

This is interesting. I wonder what's in "sweet" cat treats, such as those Cat chocolate drops, that attracts them. I'd often wondered why a cat (or a dog, for that matter) would have a different form of chocolate to humans. Now I know why.

My dog loved chocolate, although he'd mainly have the doggy chocolate drops, rather than human chocolate. Not that he'd ever stick his nose up at human chocolate. He used to love it so much, it would make him drool just thinking of it (read: begging for it).

Moufette was never one to pass up a nice, cold iced tea...

Hi Mr/Mrs/Ms O'Nine. I hope you washed the glass after the lovely Moufette finished drinking.

Dom prefers Earl Grey served hot.       

Just like Captain Picard? Dom sounds awesome!

To be honest, when I first saw this thread's title, I had thoughts of an entirely different nature, such as "Just add sugar to the pot."