If you've been following WowScience's articles, you might've known this Mexican cavefish that has no eyes. Living in the dark, Mexican tetra (Astyanax mexicanus) had given up its eyes and the corresponding visual parts of the brain to conserve energy. They only "see" through sucking.
While it was believed to be due to mutations disabling vital genes involved in eye development, this recent study may have a new and surprising answer. Aniket Gore of the US’s National Institute of Child Health and Human Development and colleagues found that the blindness is due to an addition of chemical tags called methyl groups, and not because of certain disabling changes in the DNA sequences of eye development genes.
“Although a central role for DNA methylation in development and disease has been well-documented, our results suggest that epigenetic processes can play an equally important role in adaptive evolution,” the team writes. This epigenetic mechanism also allows a faster change: the removal of its eyesight.
“This is a most interesting paper,” says evolutionary biologist Douglas Futuyma of Stony Brook University in New York. Still, he still thinks that while the researchers found how the increased activity of a specific gene involved in methylation switched off the eye genes, it's still uncertain what made that gene more active. “I think it likely that there has been an alteration in DNA sequence of that gene,” he says.
“You cannot completely rule out genetic mutations,” says Eva Jablonka of Tel Aviv University, Israel. “Maybe there was genetic variation that contributed to the eye loss.”
David Shuker at the University of Edinburgh, UK, is also unconvinced by this saying, “it goes through genetically built systems". While animals affected by the environment respond through epigenetic mechanisms, these have evolved through genetic changes, he added..
“We are always finding new ways in which these processes manifest themselves,” says Shuker. “We have found lots of amazing things.”
Ooh, controversy. Keep in touch and let's see where this goes!
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