Northeastern Mexico is home to two technically distinct types of cave fish, despite belonging to the same species: those with very large eyes and those without eyes at all. But the lack of visual organs is not the only unique physical adaptation found in the “blind cave fish.” They have also evolved taste buds that are not in their mouths. Now researchers are beginning to understand when and why this evolutionary adaptation occurs.
The first thing biologists learned was Blind Mexican cavefish were discovered to have extra taste buds on their heads and jaws as early as 1967, but scientists have barely studied the evolutionary trait since then. As detailed in a study published Aug. 6 in the journal Neuroscience, Communication BiologyA team of researchers from Ohio University in Cincinnati recently traveled to Mexico to learn more about the evolution of blind cave fish (and their taste buds).
“While regression, such as loss of vision or pigmentation, is a well-studied phenomenon, the biological basis of constructive traits is less well understood,” said Joshua Gross, lead author of the study and a professor of biology at the University of California, Cincinnati, in a statement on August 15. Profile of affiliated universities.
To understand these tiny, translucent fish, Gross and his team focused on two different populations. Astyanax mexicanus They were found in the Pachón and Tinaja cave systems in Mexico. By studying their developmental cycle starting at birth, the researchers found that blind cavefish have the same number of taste buds as their land-dwelling relatives until they are about five months old. At that point, the eyeless cavefish begin to grow more taste buds on their heads and jaws until they reach maturity at 18 months and then adulthood. Because cavefish can live for more than five years, Gross theorizes that blind cavefish may develop even more over time. The increased number of taste buds gives these cavefish a much more precise sense of taste than their sighted species that live outside of caves.
[Related: How the archerfish evolved to shoot insects.]
The emergence of external taste buds also appears to correlate with when cave fish switch their diet from live food sources to other options (mainly bat droppings), given the poor food options within the cave.
“Despite the complexity of this trait, many of the taste buds in the head appear to be primarily controlled by just two regions of the genome,” Gross said.
This new discovery could provide a new avenue for studying how vertebrates evolved specific sensory organs. For now, though, researchers are still not sure what adaptive or functional relevance the addition of taste buds to blind cave fish might have. To advance this research, Gross and his team are now studying how fish respond to different tastes, including sweet, sour, and bitter.
