GULF TIMES (Doha, Qatar) 10 May 08 Gripping facts about the gecko, from toes to tail (Roxana McLennan)

Have you ever wondered about those little climbing lizards you share your house with? These harmless and interesting animals inspire a diverse range of emotions in human observers, from fear and loathing to enthusiasm bordering on fanaticism.

Dr Drew Gardner, an associate professor at Zayed University in Abu Dhabi currently lecturing in Biology and Environmental Science, presented a well-attended talk to the Qatar Natural History Group (QNHG) on Wednesday on the topic of the geckos of south-eastern Arabia. The talk was illustrated with vibrant photographs of the geckos from the region.

Geckos are most renowned for their remarkable climbing skills, which let them ascend vertical walls, walk upside down on ceilings and even cross panes of glass.

Detailed study has revealed that the gecko toe pads do not use suction or glue, or even friction from microscopic irregularities in surfaces (climbing geckos can just as easily walk on super-polished glass or Teflon).

Instead, each of the specialised scales (scansors) on the underside of the toes has up to 150,000 microscopic hair-like projections called setae. Each toe may have 10 or 20 of these scales.

The setae, each about 1/10th the diameter of a human hair, branch at several levels, giving rise to hundreds of saucer-shaped end plates. A large gecko has millions of these. Adding up the setae on all the toes, the total surface area is huge.

Recent research has shown that the adhesion is mainly due to ‘van der Waals forces’ which are attractive forces at the atomic level. Species which live on vertical rock or trees usually have adhesive toe pads, while those that live on rocky ground or on sand have no need for such devices, and have more usual lizard toes.

Despite their unwarranted reputation for biting and being poisonous, Gardner explained that geckos actually have few defences against their enemies and are harmless to humans.

No gecko, nor indeed any lizard in Qatar, is poisonous; the small teeth of even the largest gecko species are hardly able to break human skin.

Geckos have many enemies in the guise of snakes, birds, foxes and other predators. Their trump card is their ability to shed their tails.

Even the slightest pull on the tail leaves the detached tail wriggling vigorously in the hand or on the ground, while the tail owner makes good its escape. The gecko will re-grow the tail, although the new one never quite matches the original.

Another trick is shown by the Wonder gecko Teratoscincus keyserlingii. These are the largest of the geckos in Arabia and the most colourful. They are probably also the most endangered as they are restricted to the area inland from Dubai and Jebel Ali.

Their scales are different, being large and overlapping and they have large scales above the tail which can produce a hissing sound as a threat.

However their defence of last resort is ‘skin autotomy’. They have a fragile skin which, if grasped, detaches from the underlying tissues and comes away. An owl or cat that tries to catch the gecko is left with a mouthful of skin, which the gecko will re-grow. A scar is a much more attractive alternative to being eaten!

Of all the known species of lizards occurring in south-eastern Arabia, almost half are geckos. Perhaps the most familiar here is the yellow-bellied house gecko, Hemidactylus flaviviridis. This is the species found in many houses in Doha.

They are plump creatures, up to about 15cm long, with pinkish brown backs and large eyes. They are usually seen at night on walls and ceilings, particularly around outside lights where they lie in wait for their prey of moths and mosquitoes.

While most lizards are ground dwellers and diurnal, the majority of geckos are nocturnal. Nocturnal geckos have large and very sensitive eyes with complex pupils that open wide at night but contract to vertical slits during the day. Geckos may even be able to see in full colour at night.

As geckos don’t have moveable eyelids, they cannot shut their eyes. They can sometimes be seen to clean them by licking them with their long, rounded tongues. Nocturnal geckos often have well developed vocal cords, sensitive ears and a repertoire of calls which may be used for territorial defence or attracting mates.

The talk concluded with a question and answer session followed by enthusiastic applause in appreciation of both Gardner’s talk and for the continued support of Khaled Mohamed al-Rabban and Rayyan Mineral Water who sponsored the talk.
Gripping facts about the gecko, from toes to tail

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