Did cavefish trade eyes for good taste?

Two eyes for a bigger jaw and a more sensitive palate. That's the evolutionary bargain seemingly struck by certain cave-dwelling fish in Mexico, according to a research group led William R. Jeffery of the University of Maryland in College Park.

The researchers study Astyanax mexicanus, a freshwater fish that has diverged into a sighted, surface-dwelling form and a blind, cave-dwelling form. The latter has eyes during its early embryonic stage, but they quickly degenerate. The cave-dwelling fish do, however, have larger jaws, more teeth, and a greater number of taste buds than their sighted relatives do.

Jeffery's team had previously shown that a protein called sonic hedgehog drives eye degeneration in cavefish embryos. The investigators have now found that this protein also controls jaw and taste bud growth in A. mexicanus. Injecting early cavefish embryos with a compound that blocks the activity of sonic hedgehog produces fish with fewer-than-normal taste buds and more rudimentary jaws, Yoshiyuku Yamamoto reports. Moreover, boosting the protein in embryos of the surface-dwelling form results in the fish having more taste buds than they otherwise would.

The researchers suggest that the multiple functions of sonic hedgehog may have enabled the cavefish to sacrifice its inessential eyes for enhancement of features more useful for finding food in the dark.--J.T.