Geckos are lizards that belong to the Class Reptilia, Order Squamata, Suborder Sauria (Lacertilia), and Infraorder Gekkota within seven families, including Carphodactylidae (seven genera, thirty species), Diplodactylidae (twenty-five genera, 137 species), Eublepharidae (six genera, thirty species), Gekkonidae (fifty-four genera, 1,264 species), Pygopodidae (eight genera, thirty-five species), Phyllodactylidae (nine genera, 100 species), and Sphaerodactylidae (twelve genera, 200 species). By far, the true geckos (Gekkonidae) are the largest family of lizards. Many common geckos are members of this family, including dtellas (Gehyra), house geckos (Hemidactylus), true geckos (Gekko), and day geckos (Phelsuma). Geckos are cosmopolitan in distribution and are particularly species-rich in the tropics. At least one type of gecko is found in Arkansas.
Geckos probably evolved in the Lower Cretaceous, and the earliest fossil (entombed in amber) is from Hukawng Valley, Myanmar, named Cretaceogekko burmae, dated to be 97 to 110 million years old. Reptiles come from the same common ancestors, and the earliest reptiles came about during the Carboniferous Period, about 300 to 350 million years ago. Geckos are ideal models to study sex chromosome evolution because they possess all major vertebrate sex-determining mechanisms and exhibit an extraordinary number of transitions among those mechanisms.
Most geckos typically range from 1.6 to 60 cm (0.64 to 24 in.). The largest species, the extinct kawekaweau (Hoplodactylus delcourti), is only known from a single, stuffed specimen found in the basement of Museum d’Histoire Naturelle in Marseille, France. The specimen belonged to a group of geckos, the Carphodactylini, that occur only in New Caledonia, New Zealand, and the eastern seaboard of Australia. This gecko was 60 cm (24 in.) long, and it likely inhabited native forests. It was probably wiped out along with much of the native fauna of these islands in the late nineteenth century when new invasive species such as rats and goats were introduced into the country during European colonization. The largest extant gecko is the New Caledonian giant gecko (Rhacodactylus leachianus) endemic to New Caledonia at 30 cm (12 in.) in total length. One of the smallest geckos, the Jaragua sphaero (Sphaerodactylus ariasae) is 1.6 to 1.8 cm (0.63 to 0.71 in.) long. It was discovered in 2001 off the Dominican Republic and nearby forested Beata Island and in Puerto Rico. Another tiny gecko is the Virgin Islands dwarf gecko (S. parthenopion), found on three of the British Virgin Islands: Virgin Gorda, Moskito, and Tortola islands. It measures 1.8 cm (0.71 in.) from its snout to its vent and is nearly as small as a dime.
Some unique characteristics of geckos (except species in the family Eublepharidae) are that they cannot blink (lacking eyelids), but often lick their eyes to keep them clean and moist. Too, their color vision in low light is 350 times more sensitive than human color vision. They also use a multifocal optical system that allows them to generate a sharp image for at least two different depths. Geckos are also known for their ability to communicate vocally, particularly those in the family Gekkonidae. Most of them use chirping or clicking sounds in their social interactions, while Tokay geckos (Gekko gecko) are known for their distinctive call not present in other species.
Geckos use various mechanisms to escape predation. One genus, Ptychozoon, is composed of arboreal geckos from Southeast Asia and is also known as flying or parachute geckos. They have unique wing-like flaps from the neck to the upper leg to help them conceal themselves on trees and provide lift while jumping. Also, most gecko species can lose their tails as a defensive mechanism, a process called caudal autotomy. In one study, however, there was an energetic cost, as tailed females had over twice as many reserve calories for egg production than tailless females. 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 in houses. Too, the toes of geckos appear to be “double jointed,” but this is more properly called digital hyperextension. Gecko toes can hyperextend in the opposite direction from human fingers and toes.
Geckos are well known in warm tropical regions of the world, where several species make their home inside human habitations. For example, various house geckos have become a part of indoor habitants and are often welcome, as they feed on insects, including nuisance mosquitoes. Geckos hunt using a combination of chemical and visual cues. In terms of food, geckos are mostly opportunistic and feed on a variety of prey items (mostly arthropods), including crickets, beetles, moths, and roaches, but some larger species take small vertebrate prey. When geckos are able to locate fresh fruit, honey, and flower nectar, some will dine on them.
Like other reptiles, geckos are ectothermic, producing very little metabolic heat. Essentially, a gecko’s body temperature is the same as or dependent on its environment. Like all lizards, geckos shed their skin at fairly regular intervals, with species differing in timing and method. For example, leopard geckos (Eublepharis macularius) shed at about two- to four-week intervals, and the presence of moisture aids in the shedding. When shedding begins, the gecko speeds up the process by using its teeth to detach loose skin from its body and eating it. For juvenile geckos, shedding occurs more frequently, once a week, but when they are fully grown, they shed once every one to two months.
Regarding reproduction, males of some species attract females by calling. This reaches an extreme in Ptenopus spp. (bell geckos) of southern Africa, in which males take part in choruses. Individual males try to attract females by calling from their burrow entrances, which serve as resonating chambers to amplify the sound. Less vocal geckos, such as leopard geckos, can identify females by chemical cues, and many others identify mates visually at close range. Males also lick or rub females before mating and restrain them by biting them on the nape of the neck or the back during copulation. Most geckos are oviparous, and the females generally lay one or two eggs in a clutch. Most reproduce once per year, although some like the leopard or Tokay gecko may produce four to six clutches per year. Females deposit their eggs in protected locations under rocks, logs, or tree bark. The white, sticky eggs have soft, pliable shells that quickly harden once they’re exposed to air. Depending on the species, the eggs incubate for thirty to eighty days before the fully formed hatchling geckos emerge.
A few species (Diplodactylidae) are ovoviviparous, giving birth to live young. They include the jewelled gecko (Naultinus gemmeus), a threatened species of gecko endemic to the South Island of New Zealand; Auckland green gecko (N. elegans), found only in the northern half of the North Island of New Zealand; cloudy gecko (Mokopirirakau nebulosus), found on Stewart and outlying islands, New Zealand; and goldstripe gecko (Woodworthia chrysosiretica), found in the Taranaki region and Mana Island, New Zealand. Ovoviviparous females typically reproduce once per year, giving birth to twins during the summer months.
The phenomenon of parthenogenesis permits female geckos to reproduce without mating or sperm. Parthenogenetic geckos are from all-female populations that reproduce clonally, meaning all offspring are genetic clones of their mother. These species are believed to have evolved when two different species hybridized (crossed). Two examples of parthenogenetic species are the mourning gecko (Lepidodactylus lugubris) of coastal areas of the Indian Ocean and Pacific Ocean and Australian Bynoe’s gecko (Heteronotia binoei) of Australia.
Two interesting native eublepharid geckos of the southern New Mexico, Texas, and Mexico and the Big Bend region of Texas and Mexico are the Texas banded gecko (Coleonyx brevis) and reticulate banded gecko (C. reticularis), respectively. They have functional eyelids, lack expanded toepads, and are largely terrestrial. Their preferred habitat includes dry, rocky areas, crevices, and under debris.
The legless snake, or flap-footed lizards (family Pygopodidae), are types of geckos with reduced or absent limbs. They have unusually long, slender bodies, giving them a strong resemblance to snakes. Like most geckos, they have no eyelids, but unlike snakes, they have external ear holes and flat, un-forked tongues. They are native to Australia and New Guinea.
Several species of house geckos have become an invasive concern. For example, the Indo-Pacific house gecko (Hemidactylus garnotii), tropical house gecko (H. mabouia), Mediterranean house gecko (H. turcicus), Asian flat-tailed house gecko (H. platyurus), and Sri Lankan house gecko (H. parvimaculatus) are found in houses throughout the tropics, and have become invasive in various states in the southern United States. Other non-native species that have been reported from the United States include the following: Bibron’s sand gecko (Chondrodactylus bibronii), Turner’s thick-toed gecko (C. turneri), golden gecko (Gekko badenii), Gekko gecko, Madagascan day gecko (Phelsuma grandis), gold-dust day gecko (P. laticauda), rough-tailed gecko (Cyrtopodion scabrum), ashy gecko (Sphaerodactylus elegans), reef gecko (S. notatus), ocellated gecko (S. argus), yellow-headed gecko (Gonatodes albogularis), ring-walled gecko (Tarentola annularis), and T. mauritanica. Most of these have been reported from southern Florida. In Arkansas, H. turcicus has been reported from at least twelve counties of the state and has become established with hatchlings observed at several sites.
Geckos are hosts of a great variety of parasites. In Arkansas, Louisiana, and Texas alone, new species of coccidians and tapeworms have been described from non-native H. turcicus. A potentially pathogenic coccidian, Cryptosporidium sp. has been reported from common giant ground geckos (Chondrodactylus angulifer), H. turcicus, and P. grandis.
For additional information:
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McAllister, Chris T., Dagmara Motriuk-Smith, Robert S. Seville, Matthew B. Connior, Stanley E. Trauth, and Henry W. Robison. “Coccidian Parasites (Apicomplexa: Eimeriidae) of Arkansas Herpetofauna: A Summary with Two New State Records.” Journal of the Arkansas Academy of Science 71 (2017): 143‒152. Online at: https://scholarworks.uark.edu/cgi/viewcontent.cgi?article=2157&context=jaas (accessed April 14, 2021).
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Chris T. McAllister
Eastern Oklahoma State College
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