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By Emily Benson
An unlikely foe has kept a marauding band of non-native geckos from taking over a tiny Mediterranean island: dust on their feet.
The stowaways to an island near Corsica are trapped on a single concrete building and are unable to leave, as dust elsewhere on the island makes them slip or stop in their tracks as they try to shake off the grime.
Most geckos can scamper up rocks and stroll across ceilings thanks to adhesive pads on their toes. But whereas some sport sticky rows that cover the bottom of each digit, others have just two adhesive spots at the tip of each toe, says Anthony Russell at the University of Calgary in Canada.
“We really didn’t know before why you’ve got these two fundamentally different designs,” Russell says. But now, a study by Russell and Michel-Jean Delaugerre at the Conservatoire du Littoral in Bastia, France, hints at an answer.
The pair examined two gecko species on Giraglia, a 10-hectare island off the northern coast of Corsica.
Euleptes europaea has toe-tip pads and is native to the island, roaming freely across the dusty landscape. Conversely, Tarentola mauritanica is a larger gecko with full-toe pads, and is native to other parts of the Mediterranean. The authors found that the invader was confined to a single concrete structure.
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T. mauritanica is usually an aggressive colonizer, Russell says, so at first he was puzzled as to why this species did not seem to venture far from the concrete building.
Dust trap
It emerged that the landscape itself was holding the geckos back: when the lizards scurried across the island’s crumbly stone, dust quickly fouled their toe pads, immobilizing them.
In less dusty situations, full-toe-padded geckos can shed grime from their feet by walking through a relatively clean area. But the only place to do that on Giraglia’s powdery surface is the concrete building.
The native geckos deal with the dust by lifting their small toe pads to the side, relying only on their claws for climbing. The invading geckos, however, cannot roll up their large pads without also pulling up their claws.
It’s possible that geckos with larger pads are better climbers in non-dusty environments, whereas small pads give geckos more flexibility, allowing them to climb in both dusty and non-dusty habitats.
Russell, A. P. and Delaugerre, M.-J Journal of Zoology DOI: 10.1111/jzo.12390 (2016)
Understanding the details of how geckos’ sticky toes work is crucial for biomimicry projects, such as attempts to create a Spider-Man suit or a crawling robot, says Tony Gamble at Marquette University in Milwaukee, Wisconsin. “If it’s going to climb on dusty rocks, you better have a different design than if it’s going to be climbing up buildings,” Gamble says.
Timothy Higham at the University of California, Riverside, praises the findings: “It’s a big breakthrough in gecko biology and our understanding of adhesion in geckos.”
The next step, he adds, is to study more species with pads on the tips of their toes to see whether they too thrive in dusty habitats where other geckos cannot go.
Journal reference: Journal of Zoology, DOI: 10.1111/jzo.12390
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