Blind Mexican Cavefish Genome May Provide Insight to Human Eye Disease

University of Cincinnati biologists’ recent research lists candidate genes for the evolutionary characteristics of the blind Mexican cavefish,

Astyanax mexicanus

. The candidate genes are genes that may be responsible for the development of certain evolutionary traits of the blind Mexican cavefish. The research results are part of an article published in

Nature Communications.

UC Department of Biology’s Professor Joshua B. Gross and the senior doctorate student in his lab, Bethany Stahl, played a large role in researching and contributing to the article titled “The Cavefish Genome Reveals Candidate Genes for Eye Loss.” The significance of their research is evident with its publication in one of the top scientific journals.

Their article discusses the unusual traits these fish developed over the course of 3 to 8 million years of life in the subterranean, and further identifies genes that may be responsible for the evolution of these characteristics. The most dramatic traits found in these cavefish are a reduction in color pigmentation and eye degeneration. The blind Mexican cavefish also possess taste buds that are larger in size and number and a heightened lateral line (sensory) system, which they depend on to search for sources of food.

Furthermore, the team observed shifts in behavioral traits among these fish, especially in regard to how the species searches for food. Unlike most fish that depend on their vision to swim toward their food source, the blind Mexican cavefish will scour for food lower in the water column using their expanded taste buds and enhanced lateral line to guide them. Additionally, unlike many fish, the blind Mexican cavefish are usually in constant motion. This may be a result of the decrease in nutrient sources found in their caves, as it requires them to constantly move and forage for food.

Although the scientists from UC completed their experiments on campus, Gross and Stahl also collaborated with numerous researchers across the world for this project. In the spring of 2013 they took part in an international meeting in Mexico with all of the scientists who study the blind Mexican cavefish. It was Stahl’s first time observing the fish in their natural habitat in the Sierra de El Abra cave clusters.

While visiting the caves, the team went about half a mile into the earth and observed the cave-dwelling fish in the different bodies of water as they explored further into the cave. According to the researchers, the surface-dwelling river fish did not develop the same evolutionary traits as the fish found deeper in the caves, as the surface form does harbor a functional eye and has pigmentation. Therefore, the surface fish are not able to survive in the total darkness of the blind Mexican cavefish’s habitat because they lack these cave-associated traits.

Gross and Stahl’s research also included mapping sequences derived from both cavefish and surface fish across stages of early development to the genome. This method, called RNA-seq, was used to identify levels of differential gene expression related to eye development, which is present in the eyed, surface fish, but absent from the eyeless cave-dwelling form. The findings published in the “Nature Communications” article will have a direct impact on the community of scientists who study the cavefish as it provides them with a list of genes possibly responsible for certain evolutionary traits. Scientists can now perform gene knockouts and other molecular experiments based on these candidates to test which gene(s) cause traits such as pigmentation loss or eye degeneration.  

The research pertaining to the broad cause of evolutionary changes in the wild may also have a significant impact on humans. Through studying these extreme evolutionary systems, it’s possible to learn more about why humans develop certain evolutionary traits as well as further our understanding of the evolutionary process. Investigating the evolutionary traits in this natural cavefish system may also help explain certain human diseases including retinal dysfunction.

For more information, the entire article can be found on the

Nature Communications

website.