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Penguins Are Losing Their Sense of Taste

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Although penguins might be dressed for a classy dinner date, the dapper birds probably wouldn’t enjoy the cuisine. A recent study led by Jianzhi George Zhang at the University of Michigan in Ann Arbor found that penguins have lost three of their five different tastes. While they can still distinguish between salty and sour foods, their tastes of sweet, bitter, and umami have disappeared.

In the study, researchers screened penguin DNA for the genetic code responsible for the proteins that taste buds use to decipher the five different tastes. Surprisingly, the gene that makes a protein called Trpm5, which is necessary for interpreting sweet, bitter, and umami tastes, was missing. 

"Previous studies showed that Trpm5 doesn't function at low temperatures, so my hypothesis is that the cold Antarctic essentially made the three tastes that require Trpm5 unusable," Zhang told New Scientist. "Thus, the taste receptor genes gradually degenerated and got lost."

Zhang adds, “As far as we know, penguins are the only birds that have lost three of the five basic tastes.”

Another reason penguins may be losing their sense of taste is that they swallow their prey whole, thus rendering the taste genes redundant. Why, then, haven't they lost the other two? While the three missing tastes may be superfluous to penguins, being able to taste sourness helps them gauge whether their food is rotten, and being able to taste saltiness could help keep their salt intake in check. 

It’s not unusual for animal species to lose certain tastes—giant pandas don’t register umami, while most birds and cats can’t taste sweetness—but as of yet no animal species has ever lost all five tastes. And while we may bemoan the penguin’s loss, dolphins and whales have even more limited palates: They can only taste salt.

Harvard University’s Maude Baldwin, who led a study on hummingbirds' recovery of their sweet-sensing taste buds, tells New Scientist, “This is an exciting finding and raises a host of new questions. It will be revealing to see if other polar vertebrates also lack these tastes, and to further investigate the behavioral and anatomical consequences of widespread taste loss in penguins.”

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Big Questions
Why Do Cats Freak Out After Pooping?
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Cats often exhibit some very peculiar behavior, from getting into deadly combat situations with their own tail to pouncing on unsuspecting humans. Among their most curious habits: running from their litter box like a greyhound after moving their bowels. Are they running from their own fecal matter? Has waste elimination prompted a sense of euphoria?

Experts—if anyone is said to qualify as an expert in post-poop moods—aren’t exactly sure, but they’ve presented a number of entertaining theories. From a biological standpoint, some animal behaviorists suspect that a cat bolting after a deposit might stem from fears that a predator could track them based on the smell of their waste. But researchers are quick to note that they haven’t observed cats run from their BMs in the wild.

Biology also has a little bit to do with another theory, which postulates that cats used to getting their rear ends licked by their mother after defecating as kittens are showing off their independence by sprinting away, their butts having taken on self-cleaning properties in adulthood.

Not convinced? You might find another idea more plausible: Both humans and cats have a vagus nerve running from their brain stem. In both species, the nerve can be stimulated by defecation, leading to a pleasurable sensation and what some have labeled “poo-phoria,” or post-poop elation. In running, the cat may simply be working off excess energy brought on by stimulation of the nerve.

Less interesting is the notion that notoriously hygienic cats may simply want to shake off excess litter or fecal matter by running a 100-meter dash, or that a digestive problem has led to some discomfort they’re attempting to flee from. The fact is, so little research has been done in the field of pooping cat mania that there’s no universally accepted answer. Like so much of what makes cats tick, a definitive motivation will have to remain a mystery.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Animals
Listen to the Impossibly Adorable Sounds of a Baby Sloth
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Sometimes baby sloths seem almost too adorable to be real. But the little muppet-faced treasures don't just look cute—turns out they sound cute, too. We know what you're thinking: How could you have gone your whole life without knowing what these precious creatures sound like? Well, fear not: Just in time for International Sloth Day (today), we have some footage of how the tiny mammals express themselves—and it's a lot of squeaking. (Or maybe that's you squealing?)

The sloths featured in the heart-obliterating video below come from the Sloth Sanctuary of Costa Rica. The institution rescues orphaned sloths, rehabilitates them, and gets them ready to be released back into the wild.

[h/t The Kid Should See This]

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