Evolution in Darkness: The Mexican Blind Cavefish
Introduction
The transition from surface streams to the perpetual darkness of underwater caves has driven remarkable evolutionary changes in the Mexican blind cavefish (Astyanax mexicanus). Within the past few million years, populations migrating into caves abandoned their functional visual systems, a trait retained by their stream-dwelling counterparts. This dramatic adaptation is not unique to cavefish; troglobitic animals, including crustaceans, insects, salamanders, and spiders, have independently evolved similar traits, such as eye degeneration and heightened reliance on non-visual sensory systems.
Globally, over a hundred species of cave-dwelling fish exhibit varying degrees of blindness and other cave-specific adaptations, such as reduced pigmentation and enhanced mechanosensory abilities. The Mexican blind cavefish serves as a model organism for exploring how extreme habitats shape life through genetic, ecological, and microbiological influence
Biological evolution is often framed as a process of innovation, with emphasis placed on the development of new traits such as the legs of amphibians, the hair and mammary glands of mammals, or the large and complex brains of higher primates. However, this perspective overlooks an equally important evolutionary phenomenon: regressive evolution, or the loss of structures and traits that are no longer advantageous in a given environment. In many cases, evolutionary progress entails trade-offs. For a newly developed trait, an organism’s ancestors may have lost features that were no longer critical for survival. For instance, amphibians sacrificed the gills, scales, and tails that were essential to their aquatic ancestors, adapting instead to a terrestrial lifestyle. Blind cavefish exemplify regressive evolution through their loss of functional eyes and pigmentation. Living in absolute darkness, vision itself offers no survival advantage, while maintaining eyes and pigmentation would demand considerable metabolic energy. Natural selection, therefore, favors the loss of these structures. This evolutionary process illustrates that regressive changes are not failures of evolution but rather strategic responses to environmental pressures.
Section 1 Genetics
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Section 2 Microbiome
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References
- ↑ 1.0 1.1 1.2 Zigli DD, Brew L, Obeng-Denteh W, Kwofie S. On the Application of Homeomorphism on Amoeba Proteus. Ghana Journal of Technology. 2021 Mar 31;5(2):43-7.
- ↑ Bartlett et al.: Oncolytic viruses as therapeutic cancer vaccines. Molecular Cancer 2013 12:103.
- ↑ Lee G, Low RI, Amsterdam EA, Demaria AN, Huber PW, Mason DT. Hemodynamic effects of morphine and nalbuphine in acute myocardial infarction. Clinical Pharmacology & Therapeutics. 1981 May;29(5):576-81.
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- ↑ 5.0 5.1 Murphy A, Barich D, Fennessy MS, Slonczewski JL. An Ohio State Scenic River Shows Elevated Antibiotic Resistance Genes, Including Acinetobacter Tetracycline and Macrolide Resistance, Downstream of Wastewater Treatment Plant Effluent. Microbiology Spectrum. 2021 Sep 1;9(2):e00941-21.
Edited by [Author Name], student of Joan Slonczewski for BIOL 116, 2024, Kenyon College.
