Temporal range: 110 Ma – Recent
|Gold dust day gecko|
Geckos are lizards belonging to the infraorder Gekkota, found in warm climates throughout the world. They range from 1.6 cm to 60 cm. Most geckos cannot blink. They have a fixed lens within each iris that enlarges in darkness.
Geckos are unique among lizards in their vocalizations. They use chirping sounds in social interactions with other geckos. They are the most species-rich group of lizards, with approximately 1,500 different species worldwide. The New Latin gekko and English gecko stem from the Indonesian-Malay gēkoq, which is imitative of the sound the animals make.
All geckos, excluding the Eublepharidae family, lack eyelids and instead have a transparent membrane, which they lick to clean. Nocturnal species have excellent night vision; their eyes are 350 times more sensitive to light than the human eye.
Most gecko species can lose their tails in defense, a process called autotomy. Many species are well known for their specialized toe pads that enable them to climb smooth and vertical surfaces, and even cross indoor ceilings with ease (one hypothesis explains the ability in terms of the van der Waals force). These antics are well-known to people who live in warm regions of the world, where several species of geckos make their home inside human habitations. These species (for example the House Gecko) become part of the indoor menagerie and are often welcome guests, as they feed on insects, including mosquitoes. Unlike most lizards, geckos are usually nocturnal and are great climbers.
The largest species, the Kawekaweau, is only known from a single, stuffed specimen found in the basement of a museum in Marseille, France. This gecko was 60 cm (24 in) long and it was likely endemic to New Zealand, where it lived in native forests. It was probably wiped out along with much of the native fauna of these islands in the late 19th century, when new invasive species such as rats and stoats were introduced to the country during European colonization. The smallest gecko, the Jaragua Sphaero, is a mere 1.6 cm long and was discovered in 2001 on a small island off the coast of the Dominican Republic.
Common traits 
Geckos come in various patterns and colors and are among the most colorful lizards in the world. Some species can change color and may be lighter in color at night. Some species are parthenogenic, which means the female is capable of reproducing without copulating with a male. This improves the gecko's ability to spread to new islands. However, in a situation where a single female gecko populates an entire island, the island will suffer from a lack of genetic variation within the geckos that inhabit it. The gecko's mating call sounds like a shortened bird chirping which attracts males, when they are nearby.
Shedding or moulting 
All geckos shed their skin at fairly regular intervals, with species differing in timing and method. Leopard geckos will shed at about 2 to 4 week intervals. The presence of moisture aids in the shedding. When shedding begins, the gecko will speed the process by detaching the loose skin from its body and eating it. 
Adhesion ability 
The toes of the gecko have a special adaptation that allows them to adhere to most surfaces without the use of liquids or surface tension. A recent discovery shows that geckos have a special secretial gland that allows them to absorb and excrete liquid to allow for maximum adherence to surfaces. The spatula-shaped setae arranged in lamellae on gecko footpads enable attractive van der Waals forces between the β-keratin lamellae/setae/spatulae structures and the surface. 
These van der Waals interactions involve no fluids; in theory, a boot made of synthetic setae would adhere as easily to the surface of the International Space Station as it would to a living room wall, although adhesion varies with humidity. The setae on the feet of geckos are also self-cleaning and will usually remove any clogging dirt within a few steps. Teflon, which has very low surface tension, is more difficult for geckos to adhere to than many other surfaces.
Geckos' toes seem to be "double jointed", but this is a misnomer. Their toes actually bend in the opposite direction from human fingers and toes. This allows them to overcome the van der Waals force by peeling their toes off surfaces from the tips inward. In essence, this peeling action alters the angle of incidence between millions of individual setae and the surface, reducing the Van der Waals force. Geckos' toes operate well below their full attractive capabilities most of the time. This is because there is a great margin for error depending upon the roughness of the surface, and therefore the number of setae in contact with that surface.
Use of small van der Waals attraction force requires very large surface areas: every square millimeter of a gecko's footpad contains about 14,000 hair-like setae. Each seta has a diameter of 5 micrometers. Human hair varies from 18 to 180 micrometers, so a human hair could hold between 3 and 36 setae. Each seta is in turn tipped with between 100 and 1,000 spatulae. Each spatula is 0.2 micrometer long (one five-millionth of a meter), or just below the wavelength of visible light.
The setae of a typical mature 70 g (2.5 oz) gecko would be capable of supporting a weight of 133 kg (290 lb): each spatula can exert an adhesive force of 5 to 25 nN. The exact value of the adhesion force of a spatula varies with the surface energy of the substrate it adheres to. Recent studies  have moreover shown that the component of the surface energy derived from long-range forces, such as van der Waals forces, depends on the material's structure below the outermost atomic layers (up to 100 nm beneath the surface); taking that into account, the adhesive strength can be inferred.
Recent studies have also revealed that apart from the setae, phospholipids – fatty substances produced naturally in their body – also come into play. These lipids lubricate the setae and allow the gecko to detach its foot before the next step.
About 60% of gecko species have adhesive toe pads; such pads have been gained and lost repeatedly over the course of gecko evolution. Adhesive toepads evolved independently in about 11 different gecko lineages and were lost in at least nine lineages.
Taxonomy and classification 
- Family Pygopodidae
- Family Carphodactylidae
- Family Diplodactylidae
- Family Sphaerodactylidae
- Family Phyllodactylidae
- Family Eublepharidae
- Family Gekkonidae
Species of geckos 
There are approximately 1,500 species of gecko worldwide. Following is a list of some familiar or notable species:
- Coleonyx variegatus, western banded gecko – Native to the southwestern United States and northwest Mexico.
- Cyrtopodion brachykolon, bent-toed gecko – Found in northwestern Pakistan, it was first described in 2007.
- Eublepharis macularius, leopard gecko – The most common gecko kept as a pet, it does not have adhesive toe pads and cannot climb the glass of a vivarium.
- Gehyra mutilata (Peropus mutilatus), stump-toed gecko – Able to vary its color from very light to very dark to camouflage itself, this gecko is at home in the wild as well as in residential areas.
- Gekko gecko, Tokay gecko – A large, common, Southeast Asian gecko that is known for its aggressive temperament, loud mating calls, and bright markings.
- Hemidactylus, genus of geckos in which there are many varieties.
- Hemidactylus frenatus, common house gecko – A species that thrives around man and human habitation structures in the tropics and subtropics worldwide.
- Hemidactylus garnotii, Indo-Pacific gecko – This species is found in houses throughout the tropics, and has become an invasive species of concern in Florida and Georgia in the US.
- Hemidactylus turcicus, Mediterranean gecko – Frequently found in and around buildings, it is an introduced species in the US.
- Lepidodactylus lugubris, mourning gecko – Originally an East Asian and Pacific species, it is equally at home in the wild and residential neighborhoods.
- Pachydactylus bibroni, Bibron's gecko – Native to southern Africa, this hardy arboreal gecko is considered a household pest.
- Phelsuma laticauda, gold dust day gecko – A diurnal subspecies of gecko, it lives in northern Madagascar and on the Comoros. It is also an introduced species in Hawaii.
- Ptychozoon – A genus of arboreal geckos from Southeast Asia also known as flying geckos or parachute geckos, they have wing-like flaps from the neck to the upper leg to help them conceal themselves on trees and provide lift while jumping.
- Rhacodactylus, genus of geckos native to New Caledonia.
- Sphaerodactylus ariasae, dwarf gecko – Native to the Caribbean islands, it is the world's smallest lizard.
- Tarentola mauritanica, crocodile gecko or Moorish gecko – Commonly found in the Mediterranean region from the Iberian Peninsula and southern France to Greece and northern Africa, their most distinguishing characteristics are their pointed head, spiked skin, and tail resembling that of a crocodile.
- Arnold, E.N.; Poinar, G. (2008). "A 100 million year old gecko with sophisticated adhesive toe pads, preserved in amber from Myanmar (abstract)". Zootaxa. Retrieved August 12, 2009.
- Borsuk-Białynicka, M. (1990). "Gobekko cretacicus gen. et. sp. n., a new gekkonid lizard from the Cretaceous of the Gobi Desert". Acta Palaeontologica Polonica 35 (1–2): 67–76.
- Conrad, Jack L.; Norell, Mark A. (1 December 2006). "High-resolution X-ray computed tomography of an Early Cretaceous gekkonomorph (Squamata) from Öösh (Övörkhangai; Mongolia)". Historical Biology 18 (4): 405–431. doi:10.1080/08912960600679570.
- Conrad, Jack L. (3 June 2008). "Phylogeny and Systematics of Squamata (Reptilia) Based on Morphology". Bulletin of the American Museum of Natural History 310: 1–182. doi:10.1206/310.1.
- Bauer, Aaron M.; Böhme, Wolfgang; Weitschat, Wolfgang (April 2005). "An Early Eocene gecko from Baltic amber and its implications for the evolution of gecko adhesion". Journal of Zoology 265 (4): 327–332. doi:10.1017/S0952836904006259.
- http://reptile-database.reptarium.cz/advanced_search?taxon=gecko&submit=Search Geckos in the Reptile Database
- gecko, n. Oxford English Dictionary Second edition, 1989; online version September 2011. Accessed 29 October 2011. Earlier version first published in New English Dictionary, 1898.
- Badger, David (2006). Lizards: a Natural History of Some Uncommon Creatures. St. Paul, MN: Voyageur Press. p. 47. ISBN 0760325790.
- Roth, L.S.V.; Lundstrom, L.; Kelber, A.; Kroger, R. H. H.; Unsbo, P. (1 March 2009). "The pupils and optical systems of gecko eyes". Journal of Vision 9 (3): 27–27. doi:10.1167/9.3.27.
- Piper, Ross (2007). Extraordinary Animals: an Encyclopedia of Curious and Unusual Animals. Westport, Conn.: Greenwood Press. p. 143. ISBN 0313339228.
- Santos, Daniel; Matthew Spenko, Aaron Parness, Kim Sangbae, Mark Cutkosky (2007). Journal of Adhesion Science and Technology 21 (12-13): 1317–1341 http://www.brill.nl/journal-adhesion-science-and-technology
|url=missing title (help). "Gecko "feet and toes are a hierarchical system of complex structures consisting of lamellae, setae,and spatulae. The distinguishing characteristics of the gecko adhesion system have been described [as] (1) anisotropic attachment, (2) high pulloff force to preload ratio, (3) low detachment force, (4) material independence, (5) self-cleaning, (6) anti-self sticking and (7) non-sticky default state. ... The gecko's adhesive structures are made from ß-keratin (modulus of elasticity [approx.] 2 GPa). Such a stiff material is not inherently sticky; however, because of the gecko adhesive's hierarchical nature and extremely small distal features (spatulae are [approx.] 200 nm in size), the gecko's foot is able to intimately conform to the surface and generate significant attraction using van der Waals forces."
- Huber, G.; Mantz, H.; Spolenak, R.; Mecke, K.; Jacobs, K.; Gorb, S.N. and Arzt, E. (2005). "Evidence for capillarity contributions to gecko adhesion from single spatula nanomechanical measurements". Proceedings of the National Academy of Sciences 102 (45): 16293–6. doi:10.1073/pnas.0506328102. PMC 1283435. PMID 16260737.
- Chen, B.; Gao, H. (2010). "An alternative explanation of the effect of humidity in gecko adhesion: stiffness reduction enhances adhesion on a rough surface". Int JAppl Mech 2: 1–9. doi:10.1142/s1758825110000433.
- Puthoff, J.B.; Prowse, M.; Wilkinson, M. and Autumn, K. "Changes in materials properties explain the effects of humidity on gecko adhesion". Journal of Experimental Biology 213: 3699–3704. doi:10.1242/jeb.047654.
- Prowse, M.S. "Effects of humidity on the mechanical properties of gecko setae". Acta Biomaterialia 7: 733–738. doi:10.1016/j.actbio.2010.09.036. PMID 20920615. Unknown parameter
- Hansen, W. R.; Autumn, K. (2005). "Evidence for self-cleaning in gecko setae". PNAS 102 (2): 385–389. doi:10.1073/pnas.0408304102. PMC 544316. PMID 15630086. "Setae occur in uniform arrays on overlapping lamellar pads at a density of 14,400 per mm2"
- How Geckos Stick to Walls.
- Why do the gecko's feet not stick to a teflon surface?.
- Autumn, Kellar; Sitti, M.; Liang, Y.A.; Peattie, A.M.; Hansen, W.R.; Sponberg, S.; Kenny, T.W.; Fearing, R.; Israelachvili, J.N.; and Full, R.J. (2002). "Evidence for van der Waals adhesion in gecko setae". PNAS 99 (19): 12252–12256. doi:10.1073/pnas.192252799. PMC 129431. PMID 12198184.
- "Geckos can hang upside down carrying 40kg". physics.org. Retrieved 2 November 2012.
- Autumn, Kellar (September 29, 2003). "How do gecko lizards unstick themselves as they move across a surface?". Scientific American. Retrieved 23 March 2013.
- Lee, Haeshin; Lee, Bruce P.; Messersmith, Phillip B. (2007). "A reversible wet/dry adhesive inspired by mussels and geckos". Nature 448 (7151): 338–341. doi:10.1038/nature05968. PMID 17637666.
- Loskill, P.; Puthoff, J.; Wilkinson, M.; Mecke, K.; Jacobs, K.; Autumn, K. (September 2012). "Macroscale adhesion of gecko setae reflects nanoscale differences in subsurface composition". J. R. Soc. Interface 10 (78): 20120587. doi:10.1098/rsif.2012.0587. PMID 22993246.
- Loskill, P.; Haehl, H.; Grandthyll, S.; Faidt, T.; Mueller, F.; Jacobs, K. (November 2012). "Is adhesion superficial? Silicon wafers as a model system to study van der Waals interactions". Adv. Coll. Interf. Sci. 179–182: 107–113. doi:10.1016/j.cis.2012.06.006. PMID 22795778.
- Hsu, P. Y.; Ge, L.; Li, X.; Stark, A. Y.; Wesdemiotis, C.; Niewiarowski, P. H.; Dhinojwala, A. (24 August 2011). "Direct evidence of phospholipids in gecko footprints and spatula-substrate contact interface detected using surface-sensitive spectroscopy". Journal of The Royal Society Interface 9 (69): 657–664. doi:10.1098/rsif.2011.0370.
- Gamble, Tony; Greenbaum, Eli; Jackman, Todd R.; Russell, Anthony P.; Bauer, Aaron M.; Castresana, Jose (June 27, 2012). "Repeated Origin and Loss of Adhesive Toepads in Geckos". PLoS ONE 7 (6): e39429. doi:10.1371/journal.pone.0039429.
- Han, D.; Zhou, K.; Bauer, A.M. (2004). "Phylogenetic relationships among gekkotan lizards inferred from c-mos nuclear DNA sequences and a new classification of the Gekkota". Biological Journal of the Linnean Society 83 (3): 353–368. doi:10.1111/j.1095-8312.2004.00393.x.
- Gamble, T.; Bauer, A.M.; Greenbaum, E.; Jackman, T.R. (July 2008). "Out of the blue: A novel, trans-Atlantic clade of geckos (Gekkota, Squamata)". Zoologica Scripta 37 (4): 355–366. doi:10.1111/j.1463-6409.2008.00330.x.
- Gamble, Tony; Bauer, Aaron M.; Greenbaum, Eli; Jackman, Todd R. (21 August 2007). "Evidence for Gondwanan vicariance in an ancient clade of gecko lizards". Journal of Biogeography. doi:10.1111/j.1365-2699.2007.01770.x.
- Gamble, T.; Bauer, A.M.; Colli, G.R.; Greenbaum, E.; Jackman, T.R.; Vitt, L.J.; Simons, A.M. (February 2011). "Coming to America: Multiple Origins of New World Geckos". Journal of Evolutionary Biology 24 (2): 231–244. doi:10.1111/j.1420-9101.2010.02184.x.
Further reading 
- Forbes, Peter (4th Estate, London 2005) The Gecko's Foot—Bio Inspiration: Engineered from Nature ISBN 0-00-717990-1 in H/B
- Zug, George. Speciation and Dispersal in a Low Diversity Taxon: The Slender Geckos Hemiphyllodactylus (Reptilia, Gekkonidae). Smithsonian Contributions to Zoology, no. 631. Washington, D.C.: Smithsonian Institution Scholarly Press, 2010.
- Gamble, T., E. Greenbaum, T.R. Jackman, A.P. Russell, and A.M. Bauer. 2012. Repeated origin and loss of adhesive toepads in geckos. PLoS ONE 7:e39429
|Wikimedia Commons has media related to: Gekkonidae|
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- Artificial Gecko feet for a Spiderman suit (BBC 2007-08-28)
- List of geckos in the Reptile Database
- Gecko Time Online Gecko Magazine