Gateway Gazette

University of Calgary Zoology Professor Uncovers Gecko Species with Evolved Foot Structure

Researcher Tony Russell finds a gecko species showing transition from grippy to sticky abilities

By Erin Guiltenane

A gecko in the gonatodes humeralis species uses its unique foot structure to cling to the slippery surface of a leaf. Images courtesy of Tony Russell
A gecko in the gonatodes humeralis species uses its unique foot structure to cling to the slippery surface of a leaf. Images courtesy of Tony Russell

Geckos, tiny lizards with an ability to adhere to nearly any surface, even with their heads facing downward, have long captured the interest of researchers and the public alike. Their special ability to stick to objects has been intensively studied for over 200 years.

Tony Russell, an expert on geckos and a professor of zoology in the Faculty of Science, recently helped to uncover a gecko species on the cusp of acquiring this phenomenal ability.

Russell notes that gecko research has accelerated rapidly over the last 10 to 15 years.

“Geckos are known to be able to stick to windows and other things,” he says. “People are fascinated about how that happens, and it has become big business to try and duplicate those mechanisms.”

The secret to geckos’ ability to stick comes from enlarged and specialized scales on the underside of their toes that carry tiny hairs called setae. These hairs are made up of stiff keratin, but their thinness makes them highly flexible. Their ends are branched into thousands of terminals that have microscopic flat spatular plates at the ends.

A close-up of a humeralis foot shows an increased surface area at the bottom of the toes, giving its feet a larger bonding surface.
A close-up of a humeralis foot shows an increased surface area at the bottom of the toes, giving its feet a larger bonding surface.

The precursors of these adhesive setae are friction-inducing microscopic spines that help the toes to grip the surface. For these geckos, “it’s like having studs on snow tires,” says Russell. “Sliding over the surface is controlled by increasing friction.”

Findings show gecko species in South America with evolved foot structure

In a paper recently published in the Journal of Morphology, Russell and his co-authors Joelle Baskerville, Tony Gamble, and Timothy Higham, observed that geckos in the genusGonatodes show the transition from enhancing frictional interactions to adhesion.

One species, Gonatodes humeralis, found in the forests of northern South America, has setae that help with adhesion but lacks the typical muscular, circulatory, and skeletal systems of their foot structure that had generally been considered to be necessary for adhesion to occur.

Its foot structure, however, has changed so that the spines have transformed into setae, creating greater surface area on the bottom of the toes, giving the feet a larger bonding surface. This species thrives in more environments, and can live higher in the canopy than its closest relatives.

“It’s using parts of the habitat that none of the other species in this genus use, and we think that it’s undergone ecological release. It’s found a key to opening up the environment,” says Russell.

Discovery began with observing a lab gecko climbing side of glass 

A humeralis gecko climbs its terrarium wall. Traditionally categorized as a gecko that lacks an adhesive system, this gecko's ability to stick to glass alerted Russell and his colleagues to the evolution of this species' foot structure.
A humeralis gecko climbs its terrarium wall. Traditionally categorized as a gecko that lacks an adhesive system, this gecko’s ability to stick to glass alerted Russell and his colleagues to the evolution of this species’ foot structure.

Russell and his colleagues originally tuned into their discovery in a laboratory, when they noticed a humeralis gecko climbing the side of its glass terrarium — even though it is categorized as a gecko that lacks an adhesive system.

“We studied the morphology of the system,” says Russell. “Understanding how the fully developed system works is enormously challenging, and has attracted the attention of large numbers of researchers, but understanding how it originated presents different kinds of challenges because most of the information about transition is lost in time.”

He compares observing the evolutionary phenomenon as being similar to understanding how a high-performance car, like a Ferrari or a Lamborghini, came to be without knowing the history of the automobile. As he puts it, “We need to uncover the key events that got it all going. That’s what matters in this study.”

Adhesion system in geckos proves to be very dynamic

Across the more than 1,400 species of geckos, the adhesion system is very dynamic. It has been invented by geckos at least 11 times and lost on at least nine occasions.

“Most of these instances of origin are way back in history,” says Russell. “In recent years, molecular evidence has clarified their evolutionary relationships, and we can now mine that pattern to seek lineages that are in the process of major evolutionary changes.”

The next steps for Russell and his colleagues involve collaborative fieldwork, and observing how the geckos behave in their natural habitats.

“We’re going to look at their capabilities and how they compare to other members of the same genus,” says Russell. “These geckos only have the basics, and they’re on the cusp of elaborating the more sophisticated system of the sticky geckos that we find so amazing.”

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Source: University of Calgary

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