Mexican tetra: Blind cave fish develop cave-specific accents
The Mexican tetra has evolved to live in a number of dark caves – and now we know that the fish in each cave use clicks to communicate in different ways
April 14, 2022
In the underground caves of northeastern Mexico, groups of blind fish seem to develop cave-specific accents. The linguistic division can eventually contribute to ongoing species formation among the fishermen.
The Mexican Tetra (Astyanax mexicanus) is not alien to diversification. It comes in two forms: one with good eyesight that lives in drenched rivers, the other blind with a transparent body, which began to develop perhaps only 20,000 years ago when some fish populated dark underground caves.
Like many fish, A. mexicanus uses noise to communicate. It produces at least six distinct sounds for this, although their significance seems to have changed among cavemen when they turned to living in the dark. A special form of sharp click used by sighted fish in aggressive encounters, for example, is produced by their blind counterparts when searching for food.
Carole Hyacinthe at Harvard University wondered if communication also varied between fish that evolved in different caves.
Hyacinthe and her colleagues analyzed 44 hours of fish talk recorded in six caves, spread over the three mountain ranges where the cave colonization is believed to have taken place independently of each other. The team focused on clicks and repeated clicks, the two most common sounds. They compared a range of acoustic values, including the length of each click, the pitch, and the speed at which several clicks were produced in succession.
They found several significant, distinct variations between the caves. Clicks were relatively high in a cave called Molino, while they were deep and flourished in a cave called Subterráneo. Fish that lived in a cave called Pachón fired clicks up to 10 times faster than in other caves, while in a cave called Tinaja, the clicks were more elongated. In a cave called Chica, where hybrid populations of surface and cave fish are believed to live, the sounds were more varied than elsewhere.
The sounds of a cave called Los Sabinos were similar to nearby Chica, but also to Subterráneo and Molino, which are found in different regions. This supports the idea that the sounds developed independently and were not related to physical proximity.
The team then used a statistical analysis commonly used in acoustics to divide sounds into groups, which also suggested separate patterns in each cave.
“This is a very exciting and creative work,” said Suzanne McGaugh of the University of Minnesota, who was not involved in the study. It would be interesting to see if the communication varies between surface populations as well, she says.
The new accents are probably the result of completely random genetic drift, says Sylvie Rétaux at the University of Paris-Saclay, a co-author of the study.
Eventually, the authors speculate, communication difficulties could contribute to species formation. Additional experiments involving audio playback would be crucial to explore this. “Maybe after a million years, it will have driven so much that they will no longer be able to understand each other,” says Rétaux.
Hyacinthe is now exploring cave fish sound production on a more fundamental level, as the mechanisms are still unknown. “Astyanax is a very good model for investigating the genetic basis for sound development, she says.
Reference: bioRxiv, DOI: 10.1101 / 2022.03.29.486255v1
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