Gecko Reflective Essay

Gecko Essay

There are about 750 species of geckos. The gecko is a small and harmless creature. These nocturnal reptiles have soft skin, and a short, stout body carrying a large head. These facts aren't what is truly interesting about the gecko. The gecko has weak limbs equipped with suction-padded digits that enable them to effortlessly climb along incredibly smooth ceilings. This ability was previously believed to be the work of capillary action in the gecko's toes, but upon recent discoveries made by U.S. scientists these magnificent little lizards utilize electrostatic forces to climb on these surfaces. Geckos have millions of microscopic hairs sprouting from their feet. These hairs are called setae, and they can split into as many as 1,000 tiny hairs. These tiny hairs are each capped with a triangular pad called a spatulae. These spatulae are roughly about the size of a small bacterium. These recent findings established that geckos use Van der Waals forces to scale even ceilings made of marble. Van der Waals forces are weak electrostatic attractions between adjacent molecules that arise from fluctuations in the positions of their electrons. Scientists discovered this by placing the gecko's feet on both hydrophillic, water-attracting, and hydrophobic, water-repelling, wafers and they measured the forces exerted by their feet. The gecko's feet were equally attracted to both surfaces, but when placed on surfaces with low molecular levels the feet slipped. The scientists believe that the geometry of the hairs on the gecko's toes makes the contact area between the toes and the surface large enough for the Van der Waals attraction to become significant.

This new discovery has led many scientists and engineers to think about using these new findings to create a revolutionary adhesive material. Geckos are now proving themselves as not only useful pets that eat unwanted insects, but also as an inspiration for these scientists and engineers to further experiment with artificial gecko spatulae. Engineer Ronald Fearing at Berkeley has created artificial gecko spatulae out of silicone rubber. He found that they stuck almost as well as the real thing. If scientists and engineers can work together to perfect these artificial spatulae there will be limitless possibilities for inventors. These adhesives can be used on robots so they can traverse any surface in space, or, since these spatulae can work in a vacuum, astronauts could use them inside the weightless shuttle. These synthetics could also revolutionize the whole idea of mountain climbing by using them to create a new line of shoes and gloves.

Physics is a field of science that most refer to as that...

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Wild geckos are often located by night spotlighting; where researchers use torches to either spot the animals’ body amongst vegetation or to spot “eye shine” – that is, the way that a gecko’s eye will shine (usually pink) when a torch is pointed at it. It looks a bit similar to the type of eye shine that you sometimes see when mammals run in front of your car’s headlights, but the mechanism is actually different. Let’s explore…

The reason why cats’, dogs’, cows’, sheeps’, racoons’, some insects’, some birds’, some fishs’ etc… eyes shine brightly in the dark is due to the presence of a tapetum lucidum (plural: tapeta lucida, meaning “shining carpet” in latin) behind or within the retina of each eye. The purpose of this structure is to re-reflect the light back into the eye again so that it can be reabsorbed. In this way, the animal’s vision in low light is improved. The colours reflected (variously, blue, green, white, yellow, red) by the tapeta lucida differs between animals. Interestingly, it appears that the tapetum lucidum evolved independently in at least three different orders of invertebrates and vertebrates – a great example of convergent evolution.  Evolutionary speaking, this tends to be a trait seen in carnivorous or omnivorous nocturnal or crepuscular (active around dawn and dusk) animals such as cats, dogs, spiders, some birds (including the kiwi!) – presumably it helps them hunt in low-light conditions.

Of the reptiles, only Crocodilians in the families Crocodylidae (crocodiles) and Alligatoridae (alligators and caimans) have tapeta lucida* . In contrast, most reptiles do not have a tapetum. The reason why you see red light reflecting from a nocturnal geckos’ eyes is actually just light bouncing off the retina and back through the capillaries – which is why it appears pink and doesn’t have that super-shiny glow that some spiders, moths and nocturnal mammals have. Which possibly explains why we sometimes get very excited over eye-shine from other animals when looking for geckos at night – it’s just so much more dramatic.

By the way, if you were wondering about amphibians’ shiny eyes (I was), here is the low-down from Schawb et al. (2002) : “Amphibians, apparently, do not have tapeta, although a bright reflex is found in many of these species. The source of this bright reflection is unknown at present but does not conform to the currently understood mechanisms of any tapeta.”

Shine on, all you crazy diamonds!

Footnotes:

*OK I know Schawb et al. (2002) says “only crocodiles and alligators” but the species they cite is actually a caiman, which is a member of the alligator family anyways. I’m actually uncertain whether members of the 3rd Crocodilian family, the Gavialidae (gharials & false gharials) have tapeta or not!

Places cited (thanks very much):

http://www.ehow.com/info_8541210_animals-tapetum-lucidum.html

Schwab, IR; Yuen, CK; Buyukmihci NC, Blankenship, TN; Fitzgerald PG. (2002). Evolution of the tapetum. Trans. Am. Ophthalmol. Soc.100:187-200. Access online: http://www.aosonline.org/xactions/2002/1545-6110_v100_p187.pdf

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