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This article is about the type of animal. For other uses, see Gecko (disambiguation).

Gecko
Temporal range: 50 Ma - Recent, putatively as early as 110 Ma[1]
Gold dust day gecko (also known as Madagascar day geckos)
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Reptilia
Order:
Squamata
Suborder:
Scleroglossa
Infraorder:
Gekkota
Family:
Gekkonidae

Gray, 1825
Subfamilies

Aeluroscalabotinae
Eublepharinae
Gekkoninae
Teratoscincinae
Diplodactylinae

Geckos are lizards belonging to the infraorder Gekkota, found in warm climates throughout the world. They range from 1.6 cm to 60 cm.

Geckos are unique among lizards in their vocalizations, making chirping sounds in social interactions with other geckos. Geckos are the second most species rich group of lizards (after skinks), with close to 1,500 different species worldwide and many others likely yet to be discovered. The New Latin gekko and English gecko stem from the Malay gēkoq, which is imitative of the sound the animals make.[2]

All geckos, excluding the Eublepharidae family, have no eyelids and instead have a transparent membrane which they lick to clean. Many species will, in defense, expel a foul-smelling material and feces onto their aggressors. There are also many species that will drop 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, and one documented sighting in the wild in 1870. This gecko was 60 cm (24 in) long and it was 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.[3]

Common traits

Oligocene-era gecko trapped in amber

Geckos come in various patterns and colors such as purple, pink, blue, and black, and are among the most colorful lizards in the world.

Some are subtly patterned and somewhat rubbery looking, while others are brightly colored. Some species can change color to blend in with their environment or with particular temperatures. 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 around. This allows a female to reproduce with more genetic variation, by using sexual reproduction instead of asexual.

Adhesion ability

Close-up of the underside of a gecko's foot as it walks on vertical glass

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. The spatulae tipped setae on gecko footpads facilitate attractive forces called van der Waals forces to arise between the β-keratin lamellae/setae/spatulae structures and the surface.[4]

One study suggested that capillary adhesion might play a role,[5] but that hypothesis has been rejected by more recent studies.[6][7][8]

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.[7][8] The setae on the feet of geckos are also self cleaning and will usually remove any clogging dirt within a few steps.[9][10] Teflon, which has very low van der Waals forces,[11] 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 for 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.

Uroplatus fimbriatus clinging to glass.

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.[9] Each spatula is 0.2 micrometer long[9] (one five-millionth of a meter), or just below the wavelength of visible light.[12]

If a typical mature 70 g (2.5 oz) gecko had every one of its setae in contact with a surface, it would be capable of holding aloft a weight of 133 kg (293 lb):[13] each spatula can exert an adhesive force of 10 nanonewtons (0.0010 mgf).[14] Each seta can resist 10 milligrams-force (100 μN), which is equivalent to 10 atmospheres of pull.[9]

Recent studies[15] 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 which have been gained and lost repeatedly over the course of gecko evolution [16]. Adhesive toepads evolved independently in about 11 different gecko lineages and were lost in at least nine lineages.

Taxonomy and classification

The infraorder Gekkota is divided into seven families, containing numerous genera of gecko species.[17][18][19][20]

Gold dust day gecko licking nectar from the flower of a Strelitzia plant, also known as "bird of paradise."
Dwarf yellow-headed gecko, in Dar es Salaam, Tanzania

Common species of geckos

Pores on the skin are often used in classification.
Mediterranean house gecko
  • Pachydactylus, genus of geckos of which there are many species.
  • Bibron's gecko, Pachydactylus bibroni — Native to Southern Africa, this hardy arboreal gecko is considered a household pest.
  • Crocodile gecko or Moorish gecko, Tarentola mauritanica — very strong and heavily built for their size usually growing up to 15 cm (6 in). They are commonly found in the Mediterranean region from the Iberian Peninsula and southern France to Greece and northern Africa. Their most distinguishing characteristic is their pointed head and spiked skin with their tail resembling that of a crocodile's.
  • Cyrtopodion, genus of geckos of which there are many species.
  • Rhacodactylus, genus of Geckos of which there are a few species.
    • Suras Gecko belonging to the genus Rhacodactylus.
    • Crested gecko, Rhacodactylus ciliatus — Believed extinct until rediscovered in 1994. Gaining in popularity as a pet.
    • Gargoyle gecko, Rhacodactylus auriculatus — commonly known as the New Caledonian bumpy gecko or gargoyle gecko.
  • Gold dust day gecko (Phelsuma laticauda laticauda (Boettger, 1880) (syn. Pachydactylus laticauda Boettger, 1880)) is a diurnal subspecies of geckos. It lives in northern Madagascar and on the Comoros. It is also an introduced species in Hawaii.
  • Golden Gecko, Gekko ulikovskii — native to the warm rainforests of Vietnam.
  • Hemidactylus, genus of geckos of which many varieties belong.
    • Common House Gecko, Hemidactylus frenatus — A species that thrives around man and human habitation structures in the tropics and subtropics world wide.
    • Indo-Pacific Gecko, Hemidactylus garnotii — Also known as a fox gecko because of its long, narrow snout. This species is found in houses throughout the tropics. This gecko may eat leafcutter ants.
  • New Caledonian giant gecko, Rhacodactylus leachianus — first described by Cuvier in 1829, is the largest of the Rhacodactylus geckos.
  • Leopard gecko, Eublepharis macularius — The most common gecko kept as a pet is the leopard gecko, which does not have toe pads with setae, but rather claws. These enable it to more easily climb on rough surfaces like tree bark. This gecko cannot climb the glass of a terrarium. The leopard gecko tends to be docile and calm. This gecko can eat butterworms, cockroaches, crickets, mealworms, waxworms, and superworms.
  • Mediterranean gecko, Hemidactylus turcicus — residential and wild, introduced species (USA).
  • Mourning gecko, originally an East Asian and Pacific species, Lepidodactylus lugubris is equally at home in the wild as in residential neighborhoods. Found in Hawaii, it may have been an early Polynesian introduction. A parthenogenic species. There is a report from Hawaii of someone having seen a larger gecko of this type eating a smaller one (or rather, running away from view with a smaller gecko halfway out of its mouth) on three or more occasions.[citation needed]
  • Ptychozoon, — a genus of arboreal gecko from Southeast Asia, known as Flying Geckos or Parachute Geckos, has wing-like flaps from the neck to the upper leg, to help it conceal itself on trees and provide lift while jumping.
  • Stump-toed gecko, Gehyra mutilata (Peropus mutilatus) — This gecko, commonly referred to as a gheckl, can vary its color from very light to very dark to blend into a background. At home in the wild as well as in residential neighborhoods.
  • Tree gecko, Hemiphyllodactylus typus — Tree geckos are forest dwellers.
  • Tokay gecko, Gekko gecko — a large, common, Southeast Asian gecko known for its aggressive temperament, loud mating calls, and bright markings.
  • Western banded gecko, Coleonyx variegatus — Native to southwestern United States and northwest Mexico.
  • Dwarf gecko, Sphaerodactylus ariasae — native to the Caribbean islands, and the world's smallest lizard

References

  1. ^ Arnold, E.N., & Poinar, G. (2008). "A 100 million year old gecko with sophisticated adhesive toe pads, preserved in amber from Myanmar (abstract)" (PDF). Zootaxa. Retrieved August 12, 2009.{{cite web}}: CS1 maint: multiple names: authors list (link)
  2. ^ 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.
  3. ^ Piper, Ross (2007), Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press.
  4. ^ Santos, Daniel (2007). Journal of Adhesion Science and Technology. 21 (12–13): 1317–1341 http://www.brill.nl/journal-adhesion-science-and-technology. 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. {{cite journal}}: Missing or empty |title= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  5. ^ Huber, G.; et al. (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. {{cite journal}}: Explicit use of et al. in: |author= (help)
  6. ^ Chen, B. (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. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  7. ^ a b Puthoff, J. B.; et al. "Changes in materials properties explain the effects of humidity on gecko adhesion". J Exp Biol. 213: 3699–3704. doi:10.1242/jeb.047654. {{cite journal}}: Explicit use of et al. in: |author= (help)
  8. ^ a b Prowse, M. S.; et al. "Effects of humidity on the mechanical properties of gecko setae". Acta Biomater. 7: 733–738. doi:10.1016/j.actbio.2010.09.036. PMID 20920615. {{cite journal}}: Explicit use of et al. in: |author= (help)
  9. ^ a b c d Hansen, W. R. (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 {{cite journal}}: Cite has empty unknown parameter: |month= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  10. ^ How Geckos Stick to Walls.
  11. ^ Why do the gecko's feet not stick to a teflon surface?.
  12. ^ Autumn, Kellar (2002). "Evidence for van der Waals adhesion in gecko setae". PNAS. 99 (19): 12252–12256. doi:10.1073/pnas.192252799. PMC 129431. PMID 12198184. {{cite journal}}: Cite has empty unknown parameter: |month= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  13. ^ Kellar Autumn, Scientific American: Ask the experts. Accessed 5 June 2007.
  14. ^ Lee, Haeshin (2007). "A reversible wet/dry adhesive inspired by mussels and geckos". Nature. 448 (7151): 338–341. doi:10.1038/nature05968. PMID 17637666. {{cite journal}}: Cite has empty unknown parameter: |month= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  15. ^ Ardnt, Ingo (2012). "On Greasy Feet- What is the secret behind gecko's amazing climbing skills?". 6 (4): 14. {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |month= ignored (help)
  16. ^ 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
  17. ^ 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: 353–368.
  18. ^ Gamble, T.; Bauer, A. M.; Greenbaum, E.; Jackman, T.R. (2008). "Out of the blue: A novel, trans-Atlantic clade of geckos (Gekkota, Squamata)". Zoologica Scripta. 37: 355–366.
  19. ^ Gamble, T., A. M. Bauer, E. Greenbaum, & T.R. Jackman. 2008. Evidence for Gondwanan vicariance in an ancient clade of gecko lizards. Journal of Biogeography 35: 88-104
  20. ^ Gamble, T.; Bauer, A. M.; Colli, G. R.; Greenbaum, E.; Jackman, T.R.; Vitt, L. J.; Simons, A. M. (2011). "Coming to America: Multiple Origins of New World Geckos". Journal of Evolutionary Biology. 24: 231–244. {{cite journal}}: Cite has empty unknown parameter: |author-name-separator= (help); Unknown parameter |author-separator= ignored (help)

Further reading

Wikimedia Commons has media related to Gekkonidae.
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