American Scientist

To the Editors:

Several years ago I gave my granddaughter, Eden, a leopard gecko. Then along comes Kellar Autumn's article on geckos' sticky feet ("How Geckos Toes Stick," March-April). I suggested to Eden that we examine her gecko's feet with a hand lens, but she told me that she had never seen her gecko climb any kind of wall. Sure enough we did not see anything special about her gecko's feet.

I have combed through Dr. Autumn's article but cannot find any reference to some geckos not having sticky feet. Is there an explanation for this exception?

H. Stuart Whitney
Eden E. A. Whitney
Sooke, British Columbia, Canada

Dr. Autumn responds:

Your granddaughter is correct: leopard geckos are not good climbers. In my article, I failed to mention that while most of the 1,000 or more gecko species have adhesive pads, some do not. Some geckos lack pads because they never evolved them, while other species have evolved them away. Leopard geckos lack adhesive pads because the family they belong to (Eublepharidae) split from the gecko lineage long before setae evolved. Euplepharids retain many ancestral lizard characteristics such as eyelids and a terrestrial habitat.

Research by my colleague Anthony Russell at the University of Calgary in Canada has shown that climbing and adhesive setae evolved several times independently in geckos. Russell's work suggests that the variations on a similar theme of gecko foot design are the result of similar selective pressures on different lineages of gecko. Thus, many of the differences we observe in gecko foot design may represent different, but largely equivalent, evolutionary solutions to the problem of how to climb smooth surfaces.