Geckos are a group of almost 1,500 species of carnivorous lizards, representing the infraorder Gekkota. They are distinguished from other lizards by their distinct vocalizations, such as chirps, hisses, and clicks.
These lizards typically have a short, stout body, large head, well-developed limbs, and soft skin. Being nocturnal, they usually lack eyelids (except eyelid geckos) but possess exceptionally sensitive eyes for excellent low-light vision.
They are most commonly found in warm regions of the world, from deserts to jungles, while some species live inside human settlements, feeding on insects.
The largest gecko, Gigarcanum delcourti, measures 600 millimeters (24 inches) in length, whereas the smallest, Jaragua sphaero (Sphaerodactylus ariasae), is barely 16 millimeters (0.63 inches) long.
These lizards have a short, sturdy body with a large head and well-developed limbs.
They do not bear scales but superficially appear to have a papillose surface characterized by hair-like protuberances. These structures are up to 4 microns long and taper toward their ends.
Since geckos are nocturnal (unlike most lizards), they have extremely sensitive eyes adapted for night vision (almost 350 times more accurate than human eyes). Their eyes contain cone cells with three different photo-pigments sensitive to ultraviolet, blue, and green lights of the visible spectrum. Gecko eyes also possess a unique multifocal optical system that can generate sharp images for at least two different depths.
All gecko species, except eyelid geckos, lack eyelids and instead possess a transparent membrane called brille. Each iris has a fixed lens that enlarges in the dark to allow more light to enter the eye.
Geckos have around 100 pleurodont teeth (exclusive to the order Squamata) that are fused to the inner surface of the jaw bones. Adjacent to the full-grown teeth lie tiny, replacement teeth that develop from the odontogenic stem cell in the dental lamina. These teeth are replaced every three to four months.
Around 60% of gecko species possess adhesive toe pads comprising spatula-shaped setae, which enable them to grab onto smooth, vertical surfaces. Each square millimeter of a footpad contains about 14,000 setae, each with a diameter of 5 μm and length of 0.2 μm.
Geckos derive their name from the Indonesian-Malaysian term gēkoq, borrowed from the Malay word tokek, which refers to the sound of some species like the Tokay gecko.
All geckos are currently classified under two superfamilies and seven families containing about 125 genera.
Dibamidae, a family of legless lizards (also called blind lizards), were initially considered geckos, but recent molecular studies suggest they are a distinct lineage within Squamata.
Although geckos are mostly found in warm regions, they are found on all continents except Antarctica. While the banded gecko (Coleonyx variegatus) is most widespread in North America, the tokay gecko (Gekko gecko) is native to Southeast Asia.
These reptiles live in rainforests, deserts, and mountain slopes in the wild, while some species also inhabit artificial habitats, preferring areas with human settlements.
Most geckos are insectivorous, feeding on crickets, varieties of worms, fruit flies, moths, and grasshoppers. They can generally go without food for up to three weeks but can extend their fasting to months during winter.
Although geckos are mostly nocturnal, the members of the genus Phelsuma (day geckos) are diurnal and set out for their daily activities during the day.
Most geckos can snip off their tails (autotomy) when a predator attacks them. The wriggling autotomized part distracts the attacker, providing them enough time to flee.
These lizards shed their skin (molting) regularly by detaching it from their bodies. Young geckos shed more frequently (once a week) than adults, who shed once every one to two months. However, the timing and process of shedding the exoskeleton vary with species. For example, leopard geckos molt once every two weeks as adults.
Geckos move by rolling the setae of the adhesive toepads on the surface and shifting the setae’s angle to lift their toes quickly.
They remain inactive in winter and slow their metabolic rates to conserve energy (brumation). During this phase, geckos have low appetite and remain under shade for weeks.
Although most geckos reproduce sexually, asexual reproduction through parthenogenesis (producing an embryo without fertilization) is observed in many families, like Gekkonidae. Mating is preceded by elaborate rituals to attract potential mates in some species. For example, male Madagascar day geckos sway their heads and flick their tongues at the females, attempting to allure them. They also produce a waxy secretion from the pores on the back of their legs as a part of their courtship behavior.
After fertilization, most geckos lay small clutches of eggs; however, others, like the New Zealand common gecko, are viviparous, giving birth to live young. The newborn’s sex is determined by temperature-dependent sex determination (TDSD) or XX/XY and ZZ/ZW sets of sex chromosomes.
Small mammals primarily prey on these reptiles, including rodents, hedgehogs, weasels, stoats, ferrets, cats, possums, and pigs.
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