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Sticky business

An eastern spiny-tailed gecko (strophurus williamsi).

Image: Rishab Pillai.

Personnel Image

Written By

Mykala Wright

College

College of Science and Engineering

Publish Date

11 October 2021

Wildlife Week

When you think about geckos, you might imagine the small brown lizard whose loud and distinctive chatter fills your home of an evening. In actual fact, there are over 1,500 species of gecko worldwide — most of which live in the wild.

Geckos can thrive in a number of diverse habitats, from tropical rainforests to dry and arid deserts or even cold mountains. In all of these settings, the reptiles perform as champion climbers, seemingly defying gravity by effortlessly gripping and scaling vertical surfaces.

This Australian Wildlife Week, JCU PhD Candidate Rishab Pillai and his advisor Lin Schwarzkopf are exploring geckos’ sticky secrets.

Previous studies have determined that geckos can scale smooth surfaces because their feet are covered in millions of tiny hairs called setae. On contact with surfaces these hairs result in attachment through van der Waals forces. This means they are able to stick to surfaces just like water droplets can stick to glass, along with the help of friction.

“There has been a lot of research on gecko toe pads, but very few studies have actually looked at geckos in the wild or how they can stick to different natural substrates, especially across a range of diverse Australian microhabitats,” Rishab says.

In Australia, wild geckos can be found living in microhabitats on surfaces such as rocks, trees, bamboo and shrubs. Rishab is investigating if a gecko’s ability to move on a particular surface determines where they live.

“We are trying to find out how geckos stick to these different surfaces in nature, and leading on from that, if they’re specialised to stick to specific surfaces or if they have evolved to stick to a range of different surfaces,” he says.

A collage of gecko toe pads.
PhD Candidate Rishab Pillai measuring surface roughness in the field.
Left: A collage of the toe pads of different gecko species (Supplied by Rishab Pillai). Right: PhD Candidate Rishab Pillai measuring gecko microhabitat surface roughness in the field (Photo by Sebastian Hoeferm, supplied by Rishab Pillai).

Tacky toes

An animal’s locomotor skills impact their ability to avoid predators, attract mates and capture prey. Consequently, the habitat in which a gecko lives — and how they move around that environment — influences their survival.

Rishab says this research has given him a new perspective on habitat selection.

“When considering reptiles, people often think about shelter availability, food availability, or temperature as driving factors for where they choose to live. But what about how they interact with the surfaces they live on? Is their ability to be stickier on a certain surface something they need to consider when they explore a given habitat?”

To answer these questions, Rishab takes several approaches. He describes the research as a combination of ecology, performance (a gecko’s ability to cling) and morphology.

Firstly, Rishab visits diverse habitats across Queensland to determine where these animals live in the wild. Secondly, he quantifies the roughness or smoothness of the surfaces they occupy. And thirdly, he replicates that surface in the lab before collecting the geckos and testing their ability to grip to them.

“The last step is quantifying the morphology of each gecko toe pad. So, using a scanning electron microscope, I look at the hairs on the geckos’ feet to see how they have evolved to different lengths, diameters and densities that help them to stick to particular substrates,” he says.

So far, Rishab has discovered that there is indeed a relationship between the microhabitat a gecko chooses to live in and their ability to cling to and move around that environment.

“We’ve found that three species of velvet gecko choose microhabitats comprising of specific surface roughness,” he says. “They prefer to live on surfaces they can stick to better, where their performance is high.”

Rishab’s research has also revealed that geckos can grip to extremely smooth surfaces, such as glass, just as well as they can stick to very coarse surfaces, such as ironbark.

“The geckos do not become less sticky with increasing surface roughness, potentially highlighting the context-dependent nature of their claws and adhesive hairs,” he says.

Want to know more gripping gecko secrets? Check out Rishab’s discoveries.

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