Rhacodactylus leachianus
Conservation status
Least Concern  (IUCN 3.1)[1]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Squamata
Family:	Diplodactylidae
Genus:	Rhacodactylus
Species:	R. leachianus
Binomial name
Rhacodactylus leachianus (Cuvier, 1829)
Approximate distribution (New Caledonia, Oceania)   Range
Synonyms[2]
List Ascalabotes leachianus Cuvier, 1829 Pteropleura leachianusGray, 1831 Lomadactylus leachianusvan der Hoeven, 1833 Gecko leachiiSchinz, 1834 Platydactylus leachianus Wiegmann, 1834 Hoplodactylus leachianus Fitzinger, 1843 Rhacodactylus leachianus Bocage, 1873

Rhacodactylus leachianus, commonly known as the New Caledonian giant gecko, Leach's giant gecko, leachianus gecko, or Leachie, is the largest living species of gecko and a member of the family Diplodactylidae. It is native to most of New Caledonia.

The specific name, leachianus, is in honor of English zoologist William Elford Leach.^[3] Historically, there have been three recognized subspecies of R. leachianus (including the nominotypical subspecies): R. l. aubrianus, R. l. henkeli (first described by Seipp and Obst in 1994),^[4] and R. l. leachianus. However, based on recent molecular data, no populations of R. leachianus are granted subspecies status at the present time.^[1][5] Instead, locality based morphotypes are used to distinguish populations of R. leachianus.^[6]

R. leachianus is the largest extant gecko in the world^[7] and is considered an example of island gigantism. R. leachianus of the Grande Terre localities are capable of growing 14–17 inches (360–430 mm) long, with a weight range between 250 and 500 grams.^[6] R. leachianus of the Insular localities are capable of growing 9–12" (23–30 cm) long, and weighting between 150 and 300 grams. It has a heavy body, loose skin, and a small, stumpy tail. It is variable in color, coming in shades of mottled green, gray, and brown, sometimes with highlights of white, orange, and/or pink.^[1] It was only exceed in size by the now extinct Gigarcanum delcourti known from a single specimen 50% longer and probably several times heavier than the largest R. leachianus specimens, which also originated from New Caledonia.^[8]

R. leachianus is found in all of the southern and eastern portions of the main island of New Caledonia, as well as on several of the smaller islands in the group. Topographical and ecological differences observed at each locality may have contributed to the phenotypical and morphological differences seen in R. leachianus. The insular locality of Duu Ana is thought to no longer have an extant population of R. Leachianus.^[6]

R. Leachianus often show locality-specific phenotypical coloration, size, and morphological differences called morphotypes. The largest locality group of R. leachianus are those found on the main island of New Caledonia, Grande Terre. The localities associated with Grande Terre, often referred to as the "mainland localities", include the Yate locale, the Mount Khogis locale, the Goro locale, the Poindimie locale, and the Mount Humboldt locale. Early on, a typing system was created in attempt to group phenotypical traits seen on Grande Terre together. This typing system included Type A, Type B, and Type C R. leachianus. However, this typing system is no longer considered an accurate means of locale identification, but is still commonly used for generalization within the pet trade. Type A R. leachianus were those that had little to no patterning on the laterals, containing a dark, solid or webbed background coloration. Type B R. leachianus were those that displayed lateral patterning in the form of linear blotches, or solid-colored vertical bars, commonly paired with a dark base coloration. Type B R. leachianus were said to be the most patterned of the various types. Type C R. leachianus were those that are slow growing, large geckos, commonly paired with light blotching and a dark base color. Type C R. leachianus are reported to grow up to 17 inches in length.^[6][9]

R. leachianus are also found on the neighboring islands of Grant Terre, commonly referred to as the "insular localities". These Insular localities include the Isle of Pines locale, the Nuu Ami locale, the Nuu Ana locale, the Duu Ana locale, the Moro locale, the Bayonnaise locale, the Brosse locale, and the Caanawa locale.^[6][9]

R. leachianus found in the Yate region are recognized as one of the largest localities, being heavy bodied, bulky animals. They often have elongated tails in comparison to most other locales. Yate R. leachianus can reach above 400 grams, and grow up to 15 inches in length. they are found to have a base coloration that can range from a dark brown to golden yellow. Dark netting or thin webbing is also commonly found accompanying the base coloration. Thin, white lines may also be present on the laterals.^[9]

R. leachianus found in the Mount Khogis region are also among the largest of the locales, commonly reaching over 300 grams. Mount Khogis R. leachianus display base colorations that range from jet black to olive green. These individuals may possess enlarged scales that run the length of the snout ridges, which can be used as a differentiating factor for this locale. White blotches may also be present on the laterals, varying widely in size.^[9]

R. leachianus found in the Goro locality are a large locale, reaching up to 17 inches in length and 500 grams. Goro R. leachianus are dark in coloration, with accompanying white blotches that run vertically in rows along the lateral sides. White specking may also be present along the entire body of the individual.^[9]

R. leachianus found in the Poindimie region are often longer and leaner than other mainland localities. Poindimie R. leachianus are one of the largest localities, reaching over 400 grams. Base coloration is often variable, including greens, blacks, yellows, and browns. Little to no patterning is seen in the Poindimie locale, however, yellow or white spotting may occur with age.^[9]

R. leachianus found in the Mount Humboldt region are large bodied, bulky individuals. Base coloration is often described as variable, ranging from blacks to browns and greens. White blotches may be present, commonly covering the laterals and occasionally on the dorsal. Mount Humboldt R. Leachianus may reach up to 420 grams in weight.^[9]

R. leachianus found on the island Brosse are often referred to as one of the larger insular forms with a robust shape. The coloration is often yellow or green, with large pink or white blotching, accompanied by black flecking. this locality may be referred to as the "striped neck" locale, due to bars that begin just after the head and continue down the neck area. Brosse Locality R. leachianus can weigh roughly 250g, and measure up to 10 inches in length. The island of Brosse is also referred to as "Isle D".^[9]

R. leachianus found on the island Bayonnaise are characterized by a yellow-green base color, often displaying banding that covers the laterals and dorsal. This banding can range from thinner blotched white band to larger pink, purple, or white bands. The Island of Bayonnaise is also known as "Isle C".^[9]

R. leachianus found on the island of Nuu Ana is the smallest recorded locality of R. leachianus. Nuu Ana individuals often have shorter limbs with an overall robust appearance. The Nuu Ana locale may reach up to 9 inches in length, and remain under 200 grams. The base color can range from various shades of greenish yellow, often with large colorful blotching or barring along the entire body of the gecko. The island of Nuu Ana is also known as "Isle G".^[9]

R. leachianus found on the island of Nuu Ami are a small locale, reaching up to 200 grams. Nuu Ami R. leachianus often display a darker gray iris in comparison to other localities. Base coloration may range from deep greens to bright yellows, commonly accompanied by white or pink blotching. Nuu Ami locality R. leachianus may also have spots or blotching arranged in a "W" shape along the dorsal area. The island of Nuu Ami is also known as "Isle H".^[9]

R. leachianus found on the island of Duu Ana are characterized by their dark green-brown base coloration, along with light colored barring that lines the laterals of the gecko. Barring may also be present along the dorsal. Duu Ana R. leachianus often display morphological traits, such as larger legs in comparison to other insular localities. It is speculated that this locality may eat crabs, due to low availability of fruit matter on the island. The Duu Ana locale is thought to be extinct in the wild, though, evidence is needed. Smaller breeding populations remain in captivity. The island of Duu Ana is also known as "Isle I".^[9]

R. leachianus found on the island of Caanawa are a larger insular locality. The base coloration is often variable, ranging from browns to light green. The patterning on Caanawa R. leachianus often display deep purple blotching or barring, with a significant amount of black peppering. The island of Caanawa is also known as "Isle K".^[9]

R. leachianus found on the Isle of Pines are the largest of the Insular localities, reaching up to 12 inches in length and surpassing 300 grams. The Isle of Pines locality is often characterized by large head and neck regions, with a robust appearance. Base coloration is often deep green, but also can range from brown to yellow. This is accompanied by white blotches present on the laterals and dorsal area of the gecko. The Isle of Pines can also be referred to as "Pine Island".^[9]

R. leachianus found on the Island of Moro is one of the largest insular localities, reaching up to 12 to 13 inches in length. The Moro locality often displays a green base color, with large pink or white blotching. The head shape for the Moro locality is large with a snout that is squared off. The island of Moro is also known as "Isle E".^[9]

R. leachianus is an arboreal species; it is primarily nocturnal and remains hidden in tree hollows during the day.^[6] it has a diet that includes insects, spiders, small vertebrates, fruit, nectar, and sap. The most common component of R. leachianus diet consists of the fruit from Cassine curtipendula, a small fruit with a large seed that is often seen in fecal matter. It is speculated that the elongated snouts of mainland locality R. leachianus suggest a diet model that contains more vertebrate and insect matter than their insular locality counter-parts. Records of cannibalism among R. leachianus have been recorded, but this phenomenon could be attributed to territorial defense.^[6] These giant geckos can climb vertically up glass surfaces. This is due to adhesive pads on their feet called lamellae, which are made up of tiny hairs which increase friction force when applied to surfaces.^[10] R. Leachianus also possess large claws that aid in climbing as well. R. leachianus are capable of dropping their tail, a self-amputation process known as autotomy.^[6] Unlike Correlophus cilliatus, R. leachianus are capable of tail regeneration through a process known as epimorphosis. Males and females of R. leachianus display differentiating morphological characteristics known as sexual dimorphism. Male R. leachianus display a hemipenal bulge at the base of the tail, whereas females do not have this bulge. R. leachianus is observed to have temperature dependent sex determination. In captivity, eggs with a sustained incubated at 85 °F will often result in male offspring, and eggs that have a sustained incubation temperature of 72 °F (22 °C) will result in female offspring.^[6]

Popular lore within the enthusiast lay community has promoted the notion that R. leachianus may pair monogamously in the wild and may remain compatible and establish a pair-bond, which may last for a single breeding season or persist for several years. In captivity, some hobbyists have responded to this notion of pair-bonding by keeping successful pairs together until the animals display incompatibility (fighting, injury, abject sequester by conspecific), at which time the bond-broken animals are separated permanently or reintroduced to one another at a later date (or introduced to different animals) in an attempt to establish a new pair-bond. It remains unclear whether the pair-bond is a real phenomenon for R. leachianus. Reports from the expeditions of herpetoculturalists philippe De Vosjoli, Frank Fast, and Bill Love, provide multiple accounts of monogamous pair bonding activity, as investigated tree hollows often housed a single pair of leachianus that remained for several weeks. Breeding behavior involves biting and thrashing that can become violent, often accompanied with locking jaws. The popular notion is that these behaviors may serve to test for pair compatibility and physical capability of a mate. However, it remains unclear whether the level of savagery witnessed in captivity is present in the wild populations. The necessary limits of an otherwise healthy captive environment may disallow some natural thresholds required for the resolution of conflict between conspecifics (for example, the natural required distance of separation may exceed the space limits in a captive setting). In the wild, a male-female pair of R. leachianus will commonly reside in an otherwise unoccupied tree hollow, which the pair will defend by displaying territorial behavior, such as vocalization. Tree hollow related behavior is similar to that of hollow nesting birds. Mate identification is thought to be done through a process called scent marking.^[6] Adult females of R. leachianus usually lay two eggs at a time (universal trait for all geckos), having up to 10 clutches per year.^[6][11] Older females in captivity may not lay clutches in a breeding season, even when paired with a compatible male. However, older females can lay clutches over the course of their entire adult lifespan. Pair incompatibility in a previously compatible pair may occur, often indicated by aggressive territorial behavior and injury. There have been reports of parthenogenesis in unpaired females in captivity, with some parthenogenic offspring reaching maturity with no apparent defects.^[6]

R. leachianus have the widest range of vocalizations of any member of the gekkonidae family.^[6] R. leachianus can make a loud growling noise, and local people call it "the devil in the trees".^[11] This growling vocalization is speculated to be a warning call is often made in the presence of a predator or a rivaling R. leachianus. Clucking is another common vocalization, commonly associated with mate calling, often heard at night. A light whistle sound is used to display discomfort, or mild stress. Bird-like chirping is seen in the larger mainland localities, which incorporates a heightened stance and a gaping mouth for a threat display, often followed by a lunging motion.^[6]

Many lizards exhibit an ability to alter the hue and/or intensity of skin color (chameleons are the extreme example), and New Caledonian Geckos are no exception. This phenomenon is facilitated by pigment-containing cells called chromatophores. This is a form of camouflage and can help the gecko blend into their environments.^{[citation needed]} Various factors may contribute to this change in skin color, including the endocrine system or environmental factors such as variations in sunlight and temperature.^[10]

Some of the indigenous Kanak people of New Caledonia fear Leach's giant gecko. This is because of an old superstition which purports that it has the ability to cling to a person's body and pull out that person's soul.^[12]

Populations of the species R. leachianus have likely been reduced by habitat destruction and degradation. This process is still a threat to the species. It also faces predation by introduced species such as cats and various rodents. It is also poached. It can be electrocuted when it travels along power lines. This species is protected and it lives in several nature reserves.^[1]

The New Caledonian giant gecko is occasionally kept as a pet. Individuals in the pet trade are propagated with captive breeding; wild populations are protected. This species may live over 20 years in captivity,^[13] with some individuals reaching up to 50 years old. Selective breeding for the pet trade has continued to maintain pure locality R. leachianus in captivity, with the addition of locality cross-breeding to create desirable phenotypes, such as dramatic coloration, size, and structure.^[13][6][9]