Over thousands of years, cavefish evolved and lost their eyesight, earning them the nickname “the blind cavefish,” but some cavefish also developed an excessive number of taste buds on the head and chin.
This is evident from a new study, now published in the journal Nature Communication BiologyScientists at the University of Cincinnati have identified when taste buds appear in areas outside the oral cavity. The research was supported by the National Science Foundation.
For starters, blind cavefish evolved in cave 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 weakest eye sockets, surface fish have huge round eyes that give them a perpetually surprised expression.
Despite many obvious physical differences, the two fish are considered the same species.
“Regression, such as the loss of vision and pigmentation, is a well-studied phenomenon, but the biological basis of structural traits is less well understood,” said Joshua Gross, senior author of the paper and biologist Joshua Gross, whose laboratory is dedicated to the study of the evolution and development of cave-dwelling vertebrates.
Although scientists discovered in the 1960s that certain populations of blind cavefish had extra taste buds — on the head and chin — no further research was done into 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 mexicanusincluding two separate populations of cavefish living in the Pachón and Tinaja caves in northwestern Mexico, which are known to possess extra taste buds.
The research team found that the number of taste buds from birth to 5 months of age is comparable to that of surface fish. The taste buds then begin to increase in number, appearing in small numbers on the head and chin well into adulthood, at about 18 months.
Cavefish can live much longer than 18 months in the wild and in captivity, and the authors suspect that more taste buds are continually accumulating as the fish age.
Although the timing of taste bud appearance was similar for the Pachón and Tinaja cavefish populations, some differences were apparent regarding density and timing of expansion, Gross says. The other surprising discovery from this study, says Gross, is the genetic architecture of this trait: “Despite the complexity of this trait, it appears that more taste buds on the head are primarily controlled by just two regions of the genome.”
The increase correlates with the time when the cavefish stop eating other living foods for sustenance and start seeking other food sources, Gross says, such as bat guano. Equally fascinating, he says, is that the expansion could occur at other cave locations that lack bat populations.
With more taste buds, he says, the cavefish have a sharper sense of taste, “which is probably an adaptive trait.”
“It remains unclear what the precise functional and adaptive relevance of this enhanced gustatory system is,” says Gross, who has prompted the team to initiate new studies that focus on taste, by exposing the fish to different tastes such as sour, sweet and bitter. .
