Spiderman is unreal but geckos are realAmy Walsh (Author) Published Date : Jan 19, 2016 14:04 ET
Latest research reveals why geckos are the largest animals able to scale smooth vertical walls.
A new study, published today in PNAS, shows that in climbing animals from mites and spiders up to tree frogs and geckos, the percentage of body surface covered by adhesive footpads increases as body size increases, setting a limit to the size of animal that can use this strategy because larger animals would require impossibly big feet.
Dr David Labonte and his colleagues in the University of Cambridge's Department of Zoology found that tiny mites use approximately 200 times less of their total body area for adhesive pads than geckos, nature's largest adhesion-based climbers.
Once an animal is big enough to need a substantial fraction of its body surface to be covered in sticky footpads, the necessary morphological changes would make the evolution of this trait impractical, suggests Labonte.
The researchers say that these insights into the size limits of sticky footpads could have profound implications for developing large-scale bio-inspired adhesives, which are currently only effective on very small areas.
Larger animals have evolved alternative strategies to help them climb, such as claws and toes to grip with.
The researchers compared the weight and footpad size of 225 climbing animal species including insects, frogs, spiders, lizards and even a mammal.
We compared animals covering more than seven orders of magnitude in weight, which is roughly the same as comparing a cockroach to the weight of Big Ben, for example, says Labonte.
These investigations also gave the researchers greater insights into how the size of adhesive footpads is influenced and constrained by the animals' evolutionary history.
Labonte added that adhesive pads of climbing animals are a prime example of convergent evolution, where multiple species have independently, through very different evolutionary histories, arrived at the same solution to a problem. When this happens, it's a clear sign that it must be a very good solution.
There is one other possible solution to the problem of how to stick when you're a large animal, and that's to make your sticky footpads even stickier.
We noticed that within closely related species pad size was not increasing fast enough to match body size, probably a result of evolutionary constraints. Yet these animals can still stick to walls, says Christofer Clemente, a co-author from the University of the Sunshine Coast.
Across all species the problem is solved by evolving relatively bigger pads, but this does not seem possible within closely related species, probably since there is not enough morphological diversity to allow it. Instead, within these closely related groups, pads get stickier. This is a great example of evolutionary constraint and innovation, it was added.
Spiderman is unreal but geckos are real