(A) A Harlequin Tree Frog and (B) a Black-spotted Rock Frog (S. guttatus) in their natural habitats. Photo courtesy of Endlein T, Barnes WJP, Samuel DS, Crawford NA, Biaw AB, et al./ PLoS ONE 8(9)
If a tree frog and torrent frog (sometimes known as rock frogs) were to compete over which one had the better grip, the torrent frog would always win, according to a study published in PLOS One.
University of Glasgow researcher, Thomas Endlein, and his colleagues tested the frogs’ stickiness on a variety of surfaces and angles. Conditions ranged from smooth to rough to wet.
On dry, smooth surfaces, both species held their grip equally well, but on rough, wet surfaces, the tree frog yielded to defeat.
These recent findings help explain why torrent frogs are able to live near fast-flowing mountain and hill streams and climb wet rocks near waterfalls - places where ordinary tree frogs just can’t cut it.
So, what’s the torrent frog’s secret?
With advanced imaging to observe the attachment processes, the scientists discovered that both species use their toes, bellies and thighs to clutch the surface. However, when the surface became steeper, the torrent frogs increased the use of their bellies and thighs, pressing down, to hug the surface. At the same angle, the tree frogs’ undersides lost contact, causing them to fall.
The torrent frogs also held on better when their toe pads were under water. To find out how that was possible, Endlein and his colleagues used scanning electron microscopy to visualize and compare the shape of the cells in the toe pads of both species. Sure enough, the torrent frogs’ pad cells were slightly more elongated meaning that they could create channels to help drain excess water and fluids from underneath the pad.
So now the secret is out: The torrent frog hold on to a win and the tree frog needs to get a grip.