What happens when a community of fish becomes trapped in total darkness for hundreds of thousands of years? The Mexican tetra is a small freshwater fish found in sunlit rivers, streams, and ponds in northeastern Mexico. But, between one hundred and fifty and two hundred thousand years ago, some came to inhabit a more exotic environment: the underground pools of a system of caves.
Over generations of darkness, the subterranean fish lost the huge round eyes of their surface dwelling cousins, and the silvery pigments in their skin. They became Mexican blind cavefish. Evolutionary biologists have studied this species to learn how they evolved the loss of their eyes. But, as these fish lost their eyesight, their sense of taste also became more acute.
In 2024 a team of biologists published a study of the Mexican cavefishes’ highly developed taste sense. Like many fish blind cavefish don’t just have taste buds in their mouths; they also have them on their heads, and can taste the surrounding water. The researchers found that blind cavefish start out with about the same number of taste buds on their heads as their surface dwelling relatives. But starting at about five months of age, their taste buds begin to increase in number. This increase continues until they reach adulthood at the age of eighteen months. The increase gives the cavefish a more acute sense of taste than their surface counterparts.
The researchers identified a specific set of genes responsible for this increase, and hope this will help them learn how it evolved. They think the expanded taste bud system helps the animals find food in the dark.
This moment of science comes from Indiana University.
I'm Yaël Ksander.
