Geckos Evolved Sticky Toe Pads Repeatedly

By Chelsea Whyte on June 28, 2012 11:25 PM EDT

gecko
Geckos evolved their sticky toes many times. (Photo: Tony Gamble)

Geckos get their wall-climbing ability from microscopic hairs on their toes that allow them to cling to vertical surfaces. Many geckos have these sticky toes, but not all of them. And new research shows that even though many of the species have toe pads that look similar, these super-feet evolved as many as 11 separate times.

"Scientists have long thought that adhesive toe pads originated just once in geckos, twice at the most. To discover that geckos evolved sticky toe pads again and again is amazing," said study co-author Tony Gamble of the University of Minnesota, according to Zee News.

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Instead of one ancient ancestor growing these toes, the advantageous trait evolved in several species independently of one another, and some gecko species have even lost the ability to climb on smooth surfaces over time.

Gecko toe pads adhere through a combination of weak intermolecular forces, called van der Waals forces, and frictional adhesion. Hundreds to hundreds of thousands of hair-like bristles, called setae, line the underside of a gecko's toes. The large surface area created by this multitude of bristles generates enough weak intermolecular forces to support the whole animal, the researchers said.

The gain and subsequent loss of adhesive toepads seems associated with habitat changes; e.g., living on boulders and in trees versus living on the ground, often in sand dunes, where the feature could be a hindrance rather than an advantage. "The loss of adhesive pads in dune-dwelling species is an excellent example of natural selection in action," said senior study author Aaron Bauer.

In order to understand how the toepads evolved, the research team produced the most complete gecko family tree ever constructed, including representatives of more than 100 genera (closely related groups of species) from around the world.

There are approximately 1,400 gecko species across the globe and about 60 percent of them have adhesive toe pads. Geckos with these toepads are able to make use of vertical habitats on rocks and boulders that many other kinds of lizards can't easily get to. This advantage gives them access to food in these environments, such as moths and spiders. Climbing also helps geckos avoid predators.

Thanks to this study, we now know that the geckos are a superb example of convergent evolution, where different groups of animals independently hit upon the same traits as solutions to the same challenges, reports Discover Magazine. Faced with sheer surfaces, they have evolved subtle variants on the same adaptation, time and again. And time and again, they have lost those adaptations when the need for them disappeared.

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