Science & Technology

Why some fish have two eyes on one side of their head

If you’ve seen flounders like flounders and soles and wondered why both eyes are on one side of your head, a new study has your answer.

“Flounder is some of the weirdest vertebrate On Earth, and by changing multiple properties at once in a short period of time, they became very, very fast and strange, “says Cory Evans, an assistant professor of biological sciences at Rice University.

Of all mammals, reptiles, birds, amphibians and fish, flounder is easily the most asymmetric.Evans, Corresponding Author of Studies on the Evolution of Flatfish Minutes of the National Academy of Sciences, Says it helps keep the outlook.

“Imagine another animal,” he says. “For example, let’s say you see a squirrel while walking. eye Is here and the other is there, “he says, pointing to two locations on the same side of the face. “That squirrel is having a terrible time, and there are 800 species of these fish that do exactly that.

“The perspective helps us understand how strange these animals really are.”

Evolutionarily speaking, flounder asymmetry is not just a novelty, it is an innovation, a property that makes flatfish far away from its closest relatives.

Evans says the evolution of flounder is particularly interesting as it began as a typical symmetrical fish. They began to evolve their current form, or form, about 65 million years ago and were almost complete within 3 million years.

“We have obtained all the new colonizations of morphological space in 3 million years,” says Evans. “Look at how much time has passed since then, so it’s been a really short time that they have evolved all these new forms and all the crazy species.”

Fluid trait

In their study, Evans and co-author Rice Olivier Larouche and Sara-Jane Watson of the New Mexico Institute for Mining Technology found that close integration of the genetic traits of flounder leads to a sort of evolutionary cascade.

“Integration is where there is a high degree of correlation between characteristics. For example, changing one characteristic changes another,” says Evans. “On a macroevolutionary timescale, this is very interesting because the traits begin to co-evolve with each other. Therefore, changing one trait will change several other traits. “

He states that traits may be more integrated if their morphological development is regulated or affected by a shared gene interaction network.

“As signal transduction networks expand and embrace more and more properties, the same signaling network can theoretically be used to fill changes throughout an organism, which can change very quickly. You can, “he says. “It’s like pressing a button and flipping an entire animal at once.”

Evans, LaRouche, and Watson used several methods to stitch together the story of the evolution of flounder. One was a phylogenetic comparison that traced the evolutionary history of interspecies and interspecies traits. The phylogenetic tree has branches that indicate where the species diverge. “Usually trees are built using genetics,” says Evans. “So maybe we have a lot of genomes for all those species, and we can use it to figure out who is more closely associated with whom. Once the tree is built, you can use the tree’s branching pattern as a guide to see how its characteristics have changed over time. “

Flatfish and relatives

Kory Evans has a 3D-printed skull of Jack, a symmetrical relative of flatfish. (Credit: Jeff Fitlow / Rice)

Researchers also used a micro-CT scanner from the Evans Institute to perform 3D scans of the skulls of several flounder species. We have created a 3D morphometry model that can compare different shapes using scans. However, many flounder species are so different that it was not possible to “break them apart” by shape alone or by phylogeny alone, “says Evans.

There, researchers created complex mathematical models to track the degree of integration between different regions of the skull throughout the 65 million-year history of flounder and its relatives.

“We found that flatfish is much more integrated than non-flatfish, which means that the evolution of flatfish asymmetry has become an integrated process that essentially involves changes in the entire skull. “I will,” he says. “As the eyes moved, so did many other things, and it became additive. So, as the flounder skulls become more and more integrated, more per unit time than in previous generations. Has begun to change. “

As for why flounder evolved asymmetrically, Evans says it was not the only way to become flounder.

“Other flat fish, like stingrays, didn’t do this,” he says. “They have flattened just like pancakes. But their eyes are not both on the same side. The remora (also known as the remora) is also a flat-looking fish and they do not do it. It was. “

Given that evolution is a “survival of the fittest” race, the success of flounder evolution raises questions: is asymmetry somehow advantageous?

“I’m not going to lie,” says Evans. “I really don’t know if there are any benefits. I think I did it because I did.”

Additional co-authors include Stacy Farina of Howard University, Maria Laura Haveger of the University of North Florida, and Matt Friedman of the University of Michigan.

Support for the research came from the National Science Foundation.

Source: Rice University

Why some fish have two eyes on one side of their head

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