Blind cave fish have extraordinary taste buds that increase with age, study reveals

Over thousands of years, cavefish evolved to lose their sight, earning them the nickname “blind cavefish,” but some cavefish also developed an inordinate number of taste buds on their heads and chins.

In a new study, now published in the journal Biology of communicationsScientists at the University of Cincinnati have determined when taste buds begin to appear in areas beyond the oral cavity.

For starters, blind cavefish evolved in underground ponds in northeastern Mexico. They are pale pink and almost translucent compared to their silvery counterparts that live in surface rivers and streams. While cavefish have the most subtle outline of eye sockets, surface fish have enormous round eyes that give them a perpetually surprised expression.

Despite the many obvious physical differences, the two fish are considered the same species.

“Regression, such as loss of vision and pigmentation, is a well-studied phenomenon, but the biological basis of the constructive features is less well understood,” says the paper’s lead author, UC professor and biologist Joshua Gross, whose lab studies the evolution and development of cave-dwelling vertebrates.

Although scientists discovered in the 1960s that some populations of blind cavefish had extra taste buds (on the head and chin), no further study has been conducted on the developmental or genetic processes that explain this unusual trait, Gross says.

To determine when the extra taste buds appear, Gross and his research team looked at the species Astyanax mexicanus, including two distinct populations of cavefish that live in the Pachón and Tinaja caves in northwestern Mexico that are known to have extra taste buds.

The research team found that the number of taste buds is similar to that of surface fish from birth to 5 months of age. Taste buds then begin to increase in number and appear on the head and chin in small patches until adulthood, around 18 months.

Cavefish can live much longer than 18 months in the wild and in captivity, and the authors suspect that more taste buds continually accumulate as the fish ages.

Although the timing of taste bud appearance was similar for the Pachón and Tinaja cavefish populations, there were some differences in the density and timing of expansion, Gross says. The other surprising finding of this study, Gross says, is the genetic architecture of this trait: “Despite the complexity of this feature, it appears that most taste buds on the head are controlled primarily by just two regions of the genome.”

The increase is related to when cave fish stop feeding on other live foods and start looking for other food sources, Gross says, such as bat guano. Equally fascinating, he says, is that the expansion could be happening in other caves where there are no bat populations.

With more taste buds, he said, cavefish have a keener sense of taste, “which is probably an adaptive trait.”

“It is still unclear what the precise functional and adaptive relevance of this augmented taste system is,” says Gross, which led the team to launch new studies focused on taste, exposing fish to different flavors such as sour, sweet and bitter.