Why can't some animals taste sweet?

Hara: Why can't some animals taste sweet?

AuthorZhang Qingdan

Carnivorous bat (rat-eared bat) Sherri and Brock Fenton Photo courtesy of Zhao Huabin

When it comes to sweets, people always have little resistance, and sweetness is considered a "taste of happiness"

In order to explore the mystery, The team of Zhao Huabin, a professor at the School of Life Sciences of Wuhan University, chose bats to carry out relevant research and successfully found the answer

It is closely related to food habits

Why can humans and animals taste the taste of food? This is all thanks to receptor genes

"Taste helps animals choose food, taste receptor genes, and the evolution of function, which is often closely related to

Taking the giant panda as an example, mainly eating bamboo and not loving to eat meat, the main reason for this is that the umami receptor gene responsible for sensing the deliciousness of meat has evolved into a "false gene" after a long time, that is, a nucleotide sequence is basically the same as its corresponding normal functional gene, but it cannot synthesize the inactivated gene of functional protein and no longer plays a role, so the giant panda cannot feel the umami taste

Similarly, the sweetener receptor gene is responsible for sensing sugars in food, such as glucose, fructose, and sucrose, the three most common sugars

However, in some taxa, the sequence evolution of taste receptor genes is not used to explain the feeding ecology of animals

"We data mined the bat genome and obtained a full-length sequence

Further evolutionary analysis also revealed that the sweetener receptor gene sequences of the two types of bats evolved at a similar rate, with no significant changes

Validation from cytology and behavior

However, it is not enough to explain the feeding habits of bats by the evolutionary patterns of taste gene sequences

"We studied at the cellular level and found that the sweetener receptor gene of an insectivore bat, although not a 'pseudo gene', cannot sense carbohydrates, while fruit-eating bats can sense carbohydrates

So, at the behavioral level, is there a difference in the sweetness perception of insectivorous bats and fruit-eating bats?

The researchers performed a classic "double-cup experiment" on a fruit-eating bat (brown fruit bat) and an insectivore bat (big-footed rat-eared bat), that is, giving the bat a cup of sugary water or mashed wormwood as an experimental group and a cup of ordinary water or wormwood as a control group, observing and counting their feeding.

They found that brown fruit bats prefer sugary water, suggesting that they can taste sweet; The bigfoot rat ear bat does not have a significant preference for the amount of syrup containing or without sugar, indicating that the sweetness perception ability of the bigfoot rat ear bat is

In order to verify the rationality of the experimental system, the team added a control experiment, replacing the cup of sugary worm pulp for the insectivorous bat with a cup with the bitter compound quinine, and it turned out that the insectivore bat obviously rejected

Finally, by constructing chimeras for cell experiments, the researchers further identified the key functional domains of VFD that cause the sweetener receptors of insectivore bats to lose their sweetness sensing function

Genetic function shifts

There is no answer

Usually, a gene is gradually lost
if it is no longer needed.
The dietary habits of carnivorous bats do not intersect with sugar, but the sweetener receptor gene is still preserved, "indicating that this gene is still useful, and we speculate that it may have a functional transformation
.
" Jiao Hengwu thought
.

To find functionality, the team experimented with more than a dozen compounds and found a surprising phenomenon
.
Although behavioral and cytological experiments have demonstrated that the sweet receptors of carnivorous bats cannot sense natural sugars, these sweet receptors have the function of
sensing other compounds.

In fact, the work echoes a paper published in Science by Harvard researchers in 2014, pointing out that hummingbirds do not have a sweet receptor gene but can sense sweetness
.
"They found that one of hummingbird's umami receptors underwent a functional shift that became able to perceive sweetness
.
" Zhao Huabin pointed out, "This also means that sweet taste receptors can also be transformed into other functions, while losing their original functions
.
" ”

"It's a very amazing phenomenon, the function will change, from one function to another
.
It can be seen that the function of animal sweet receptor genes has strong evolutionary plasticity
.
Zhao Huabin said, "In the future, relevant research will be carried out on mammals and vertebrates, and there will be more discoveries
.
" ”

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