Matching ideas with paragraphs
How geckos cope with wet feet
A
Geckos are remarkable little lizards, clinging to almost any dry surface, and
Alyssa Stark, from the University of Akron, US, explains that they appear to
be equally happy scampering through tropical rainforest canopies as they are
in urban settings. ‘A lot of gecko studies look at the very small adhesive
structures on their toes to understand how the system works at the most
basic level’; says Stark. She adds that the animals grip surfaces with
microscopic hairs on the soles of their feet, which make close enough contact
to be attracted to the surface by the minute forces between atoms..
B
However, she and her colleagues Timothy Sullivan and Peter Niewiarowski
were curious about how the lizards cope on surfaces in their natural habitat.
Explaining that previous studies had focused on the reptiles clinging to
artificial dry surfaces, Stark says ‘We know they are in tropical environments
that probably have a lot of rain and geckos don’t suddenly fall out of the
trees when it’s wet.’Yet, the animals do seem to have trouble getting a grip
on smooth, wet, artificial surfaces, sliding down wet vertical glass after
several steps. The team decided to find out how geckos with wet feet cope
on both wet and dry surfaces.
C
First, they had to find out how well their geckos clung onto glass with dry
feet. Fitting a tiny harness around the lizard’s pelvis and gently lowering the
animal onto a plate of smooth glass, Stark and Sullivan allowed the animal to
become well attached before connecting the harness to a tiny motor and
gently pulling the lizard until it came unstuck. The geckos hung on
tenaciously, and only came unstuck at forces of around 20N – about 20 times
their own body weight. “In my view, the gecko attachment system is over –
designed’, says Stark.
D
Next, the trio sprayed the glass plate with a midst of water and re-tested the
lizards, but this time the animals had problems holding tight. The droplets
were interfering with the lizards’ attachment mechanism, but it wasn’t clear
how. And when the team immersed the geckos in a bath of room –
temperature water with a smooth glass bottom, the animals were completely
unable to anchor themselves to the smooth surface. ‘The toes are super –
hydrophobic’, (i.e. water repellant) explains Stark, who could see a silvery
bubble of air around their toes. But, they were unable to displace the water
around their feet to make the tight contact that usually keeps geckos in
place.
E
Then the team tested the lizard’s adhesive forces on the dry surface when
their feet had been soaking for 90 minutes, and found that the lizards could
