Cavefish: Evolution in the Dark - William Jeffery

NABT 2009. Cave animals have adapted to the challenges of life in perpetual darkness by losing their eyes and pigmentation and enhancing other sensory systems, such as taste, smell, and tactile senses. Although the sensory gains are easily explained by natural selection, the losses are more difficult to explain because they seem to have no immediate benefits. Recent studies in the Mexican cavefish (Astyanax mexicanus) show that eye degeneration is developmentally linked to adaptive gains in the gustatory system via evolutionary changes in a pleiotropic gene called "sonic hedgehog." Thus, cavefish may illustrate a general phenomenon in biology in which pleiotropy and indirect selection guide the course and extent of evolution. Another benefit for cavefish living in dark caves is the absence of predators, which promotes survival by evolving an unusual suite of feeding behaviors. These behaviors would be risky in more complex, well-lit environments, such as exist on the Earths surface, illustrating the importance of environmental complexity as a driving force in evolution.

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Science & Technology

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• NESCent
• Evolution
• NABT