The blind Mexican cave fish (or Mexican tetra) succeededStyanax mexicanus in adapting to extreme conditions; As they live in complete darkness inside extremely cold caves, they overflow with water about once a year, so food is available for them for short periods interspersed with long periods of intense hunger. These fish have lost their eyesight and their colors, and despite these difficult conditions, these fish live a relatively long life, often reaching 15 years, and genetic research today indicates that the loss of color is not just a symptom of evolution, but rather it may be a way to help these fish – endurance – generating irreplaceable energy.
Researchers at the Stewars Institute for Medical Research in Kansas, Missouri, led this possibility, led by evolutionary biologists Jaya Krishnan and Nicholas Rohner, as they mapped the changes in genetic regulation that help blind Mexican cave fish tolerate their harsh environment. Regulatory regions of DNA (those regions that do not directly produce proteins but instead control where and when other genes produce those proteins). Scientists used two techniques to compare these parts in cave fish with their counterparts in related river fish. The scientists mapped the changes in the chemical tags on the DNA strand that determine which genes were expressed, then set out to track the shifts in those regulatory regions they could identify by identifying which parts of the genetic code were open for replication and which remained folded and closed.
Susan McGough, an evolutionary biologist at the University of Minnesota, who was not involved in this new study, which was published in the journal Nature Genetics, describes Nature Genetics– The results of the study, saying: “It is a huge technological development, which will open the door to future studies on cave fish.”
Using these two techniques, the researchers were able to detect many differences in the genomes of cave fish compared to closely related fish that live near the surface of the water, and among the differences they observed was the disappearance of part of the DNA in the gene hpdbThis mutation makes cave fish unable to metabolize an amino acid known as tyrosine to synthesize the pigment melanin, which leads to the disappearance of colors from these fish, and the researchers concluded that tyrosine can convert [بدلًا من ذلك] To generate energy when the cave fish are deprived of it,” Krishnan says, “they use any substrate, when available, to generate energy to survive in this harsh environment.”
Tyrosine also helps in the production of dopamine and norepinephrine, which many animals secrete in response to stress. Previous studies on cave fish have linked the loss of pigment on the one hand, and high levels of these two hormones, and the lack of sleep needed by cave fish on the other hand, and the current study indicates that the loss of pigment It also affects your metabolism, says McGough.
And since traits like pigmentation, metabolism, and sleep depend on hormones and related chemical reactions, adaptation in one of these aspects will change all the others as well, Krishnan says, and these trade-offs are the rule rather than the exception for animals living in poor habitats. of food.