Cavefish Eye Loss: Scientists Uncover Evolutionary Mystery
Genomic Analysis Dates Cave Systems via Fish Eye Loss
New research uses the genetic history of cavefish to estimate the age of subterranean cave systems in the eastern United States, pushing back potential timelines by millions of years.
Small, colorless, and blind, amblyopsid cavefishes inhabit subterranean waters throughout the eastern United States. These fish, perfectly adapted to perpetual darkness, offer a unique window into the evolution of life in extreme environments. Now, a new study reveals that analyzing the genetic changes responsible for their blindness can also help date the caves they call home.
in an analysis of the genomes of all known amblyopsid species,researchers found that the different species colonized cave systems independently of each other and separately evolved similar traits-such as the loss of eyes and pigment-as they adapted to their dark cave environments. This parallel evolution highlights the powerful selective pressures within caves.
Their findings appear in the journal Molecular Biology and Evolution.
A Mutational Clock for Cave Age
By studying the genetic mutations that caused the fishes’ eyes to degenerate, the researchers developed a sort of “mutational clock” that allowed them to estimate when each species began losing their eyes. They found that vision-related genes of the oldest cavefish species, the Ozark cavefish (Troglichthys roses), began degenerating up to 11 million years ago.
This technique provides a minimum age for the caves that the fishes colonized.The logic is straightforward: the cavefish must have been inhabiting subterranean waters while their eyesight began devolving.They wouldn’t have started losing their eyes while living in broad daylight.
“The ancient subterranean ecosystems of eastern North America are very challenging to date using traditional geochronological cave-dating techniques, which are unreliable beyond an upper limit of about 3 to 5 million years,” says Chase Brownstein, a student in Yale’s Graduate School of Arts and sciences, in the ecology and evolutionary biology department, and the study’s co-lead author.
“Determining the ages of cave-adapted fish lineages allows us to infer the minimum age of the caves they inhabit as the fishes wouldn’t have started losing their eyes while living in broad daylight. In this case we estimate a minimum age of some caves of over 11 million years.”
Maxime Policarpo of the Max Planck Institute for Biological intelligence and the University of Basel is the co-lead author.
Reconstructing Evolutionary History
For the study, the researchers reconstructed a time-calibrated evolutionary tree for amblyopsids, which belong to an ancient, species-poor order of freshwater fishes called Percopsiformes, using the fossil record as well as genomic data and high-resolution scans of all living relevant species.
All the cavefish species have similar anatomies, including elongated bodies and flattened skulls, and their pelvic fins have either been… [article ends abruptly here in the source material]
This convergence in physical traits, coupled with the autonomous genetic pathways leading to eye loss, underscores the predictable nature of adaptation in these isolated environments.