Puberty in cave fish means taste buds sprout in strange places

Puberty in cave fish means taste buds sprout in strange places

By Elizabeth Ann Brown

In the underground caves and streams of eastern Mexico, a blind fish goes through a strange adolescence: As it nears maturity, taste buds begin to grow under its chin and on top of its head, then crawl up its back.

“This is a pretty bold amplification of the taste sensory system,” says Josh Gross, an evolutionary geneticist at the University of Cincinnati and co-author of the recent cave fish study. Nature Communications BiologyGross and his team found that the new shoots bloom around the time the fish transition from eating crustacean larvae to munching on bat droppings, the adult fish’s main diet. Gross says taste buds outside the mouth may help the fish detect bat droppings in the pitch-black, “food-starved” caves.

Moving taste buds isn’t unusual in other fish: Some damselfish have taste buds on their fins, and channel catfish have them on their bodies. And, strange as it may seem, many cells in the human body can taste, too, they just don’t transmit taste signals to the brain the way taste buds do.

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Laura Bankova, a respiratory biologist at Harvard Medical School, studies tuft cells, a type of cell dotted within human mucus tissue, such as that lining the nostrils, throat, and intestines. These “rapid response” cells activate the immune system when they sense an external threat, but many of them rely on built-in taste receptors (the same kind found in taste bud cells) to do so. Bankova points out that many potentially harmful bacteria communicate through signaling chemicals called lactones. Lactones also activate taste receptors sensitive to bitter tastes, prompting an immune response in tuft cells. What’s more, environmental allergies have also proven to be a taste problem, Bankova says, and dust mites and several types of mold can also stimulate tuft cell taste receptors.

“Throughout evolution, taste receptors have spread all over our bodies to protect us from the air we breathe and from all the stimuli we get through our mouths,” says Bankova. “They’re in the inner ear, they’re in the urethra, they’re in every place that something can get into the body.”

These “extra” taste receptors aren’t just door guards; they also taste test our systems: sweet receptors regulate insulin production in the pancreas and ensure neurons in the brain have access to enough glucose; sweet, bitter, and umami receptors in the gut regulate digestion.

Gross says it’s still a mystery which taste receptors the bat droppings activate in the blind cave fish. “With fruit bats, it might be sugars; with carnivorous bats, it might be proteins,” he says. For now, only the cave fish have signed up to try the samples.