Changing Eyes!

December 4, 2002

Here is a riddle for you:

As a baby, I have compound eyes that are sensitive to dim blue light. As a kid, my eyes are most sensitive to blue-green light. As an adult, my eyes lose their lenses and cannot form images. What am I?

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That's right! As vent crabs (Bythograea thermydron) age, their eyes change. During their lives, vent crabs inhabit different ocean depths. As larvae, the crabs live in the middle depths of the ocean and drift with plankton. When the crabs become juveniles, they sink into deeper waters. As adults, the crabs dive even deeper to live near thermal vents on the ocean floor.

To study these animals, scientists collected vent crabs in the Pacific Ocean using the submersible Alvin explorer. The researchers found that larval crabs have compound eyes similar to those of insects. The compound eyes have lenses and can focus images. At this stage, the eyes are sensitive to blue light. As the crabs age and descend to the darker ocean floor, their eyes lose their lenses. This leaves the crab with a bare retina that is very sensitive to light, but cannot form images. The eyes of juvenile and adult crabs are also more sensitive to longer wavelengths of light.

These data demonstrate how one animal adapts its sensory organs to fit its environment. The scientists believe that the changing eyes of the vent crab work with thermal and chemical senses to help the animal find a suitable home near thermal vents on the ocean floor.

Reference and further information:

  1. Jinks, R.N., Markley, T.L., Taylor, E.E., Perovich, G., Dittel, A.I., Epifanio, C.E. and Cronin, T.W. Adaptive visual metamorphosis in a deep-sea hydrothermal vent crab. Nature, 420:68-70, 2002.

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