How did the blind cavefish lose its eyes?
(chosen for Nov 2 discussion)

The Mexican tetra, Astyanax mexicanus, has been the subject of great curiosity for developmental and evolutionary biologists for decades, largely because it exists in two strikingly different forms: a surface stream-dwelling form with fully functional eyes and a cave-dwelling form that does not develop eyes and is completely blind.  The surface-dwelling eyed form is ancestral, and the lack of eyes in the cave-dwelling form has inspired much speculation regarding possible selective pressures, fitness costs, and altered developmental mechanisms that might have led to the evolution of eyeless-ness.  In 2013, experiments by Rohner and colleagues revealed an intriguing component of the origins of eyeless-ness in blind cavefish, serving up evidence that cryptic genetic variation masked from selection by a key developmental mechanism may have been expressed and exposed to selection upon introduction to novel stressors in the cave environment.   

The paper:

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