The green iguana (Iguana iguana), also known as the American iguana or the common green iguana, is a large, arboreal, mostly herbivorous species of lizard of the genus Iguana. Usually, this animal is simply called the iguana. The green iguana ranges over a large geographic area; it is native from southern Brazil and Paraguay as far north as Mexico. It is highly invasive in many subtropical and tropical environments throughout the world.
A herbivore, it has adapted significantly with regard to locomotion and osmoregulation as a result of its diet. It grows to in length from head to tail, although a few specimens have grown more than with bodyweights upward of .
Although this species is commonly kept as a pet because of its disposition and coloration, it can be challenging to care for properly. Its requirements for adequate space, lighting, and heat can be difficult for hobbyists to meet.
Taxonomy The species was first officially described by Swedish botanist Carl Linnaeus in 1758. Since then, numerous subspecies have been identified, but later classified as merely regional variants of the same species.
Using nuclear and mitochondrial DNA-sequence data to explore the phylogenic history of the green iguana, scientists from El Salvador, Mexico, and the United States studied animals collected from 17 countries. The topology of phylogeny indicated that the species originated in South America and eventually radiated through Central America and the Caribbean. The study revealed no unique mitochondrial DNA haplotypes for subspecific status, but did indicate the deep lineage divergence between Central and South American populations.
Naturalists once classified the Central American iguanas as a separate subspecies (I. i. rhinolopha), but this classification was later found to be invalid based on mitochondrial DNA, and iguanas with similar nose projections appeared randomly in other populations and interbred freely with those that do not share this trait. Genetic studies in the late 2010s still recovered I. rhinolopha as a distinct species, along with several other cryptic lineages present in I. iguana, and classifying only the South American populations may be the "true" green iguana. Two new insular subspecies (I. i. insularis and I. i. sanctaluciae) endemic to St. Lucia, Saint Vincent and the Grenadines and Grenada were also identified in 2019; a 2020 study also recovered both these subspecies as part of a distinct species, the southern Antillean horned iguana (I. insularis). That 2020 study described the Saban black iguana (I. melanoderma), which they identified to be the sister group of South American I. iguana, with the clade containing both being sister to that of I. insularis. The Reptile Database disagrees with these conclusions, and groups all of these within the green iguana, with four subspecies: I. i. melanoderma, I. i. insularis, I. i.sanctaluciae, and I. i. iguana. Indicating that consensus about the status of these elevated populations has not been reached. A species or subspecies status of I. melanoderma has been questioned, and instead proposed that for now it should be considered as part of I. i. iguana.
Etymology The word "iguana" is derived from a Spanish form of the Taíno name for the species: iwana. In some Spanish-speaking countries, males of the species are referred to as garrobo or ministro and juveniles are called iguanita or garrobito.
Distribution
The native range of the green iguana extends from southern Mexico to central Brazil, Paraguay, and Bolivia and the Caribbean; specifically Grenada, Aruba, Curaçao, Bonaire, Trinidad and Tobago, St. Lucia, St. Vincent, Montserrat, Saba and Útila. People in the native regions utilize this species for food leading to increased captive breeding efforts.
Introduced range They have been introduced to Grand Cayman, Puerto Rico, Hispaniola (in the Dominican Republic side), Saint Martin (island), Guadeloupe, Martinique, Saint Vincent and the Grenadines, Singapore, Thailand, Taiwan, Texas, Florida, Hawaii, and the U.S. Virgin Islands.Scholar search
Green iguanas colonised the island of Anguilla in 1995 after being washed ashore following a hurricane, serving as direct proof of the mechanism of oceanic dispersal in allowing species to colonise areas where they previously did not occur. Though the species is not native to Martinique, a small wild colony of released or escaped green iguanas endures at historic Fort Saint Louis.
The green iguana has been introduced from South America to Puerto Rico and is very common throughout the island, where it is considered an invasive species; in the United States, feral populations also exist in South Florida (including the Florida Keys), Hawaii, the U.S. Virgin Islands and the Rio Grande Valley of Texas.
Description
The green iguana is a large lizard and is probably the largest species in the iguana family, though a few in the genus Cyclura may match or exceed it in weight.. Animal-world.com. Retrieved on 2012-08-22. Adults typically grow to in length from head to tail. As in all iguanas, the tail comprises much of this length, and the snout-to-vent length of most green iguanas is . A typical adult male weighs around while the smaller adult female typically weighs .Rivas, J.A. (2008). Pers. comm. A few large males can reach or exceed in weight and long.Green Iguana – Iguana iguana : WAZA : World Association of Zoos and Aquariums . WAZA. Retrieved on 2012-08-22. Some specimens have even reportedly been measured at a body weight of greater than .
Green iguanas possess a row of spines along their backs and tails, which helps to protect them from predators. Their whip-like tails can be used to deliver painful strikes, and like many other lizards, when grabbed by the tail, iguanas can allow it to break, so they can escape and eventually regenerate a new one. In addition, iguanas have a well-developed dewlap, which helps regulate their body temperature. This dewlap is used in courtships and territorial displays. Green iguanas have very sharp teeth that are capable of shredding leaves and even human skin. These teeth are shaped like a leaf, broad and flat, with serrations on the edge. The similarity of these teeth to those of one of the first dinosaurs discovered led to the dinosaur being named Iguanodon, meaning "iguana tooth", and the incorrect assumption that it had resembled a gigantic iguana. The teeth are situated on the inner sides of the jawbones, which is why they are hard to see in smaller specimens.
Primarily herbivorous, green iguanas are presented with a special problem for osmoregulation; plant matter contains more potassium and as it has less dense nutritional content, more must be eaten to meet metabolic needs. As green iguanas are not capable of creating liquid urine more concentrated than their bodily fluids, like birds they excrete nitrogenous wastes as urate salts through a salt gland. As a result, green iguanas have developed a lateral nasal gland to supplement renal salt secretion by expelling excess potassium and sodium chlorides.
Geographic variation
Despite their name, green iguanas occur in different colours and types. In southern countries of their range, such as Peru, green iguanas appear bluish in colour, with bold blue markings. On islands such as Bonaire, Curaçao, Aruba, and Grenada, a green iguana's colour may vary from green to lavender, black, and even reddish brown. Green iguanas from the western region of Costa Rica are red, and animals of the northern ranges, such as Mexico, appear orange. Juvenile green iguanas from El Salvador are often bright blue, but lose this color as they get older. In southeastern Florida, they are seen occasionally in yellow and less often in orange.
Adult iguanas found on most of St. Lucia, mainly on the northeastern coast, Louvette, and Grand Anse, have many differences from other green iguana populations. They are light green with predominant black stripes. Instead of the typical orange dewlap, the iguanas of St. Lucia have a black dewlap. When compared to the common green iguana, females lay about half the number of eggs, 25 instead of 50. Scales to the back of their head, near the jawbone, are smaller. Their irises are white or cream, whereas other green iguanas have yellow irises.
Green iguanas from Guatemala and southern Mexico (which may belong to the distinct species I. rhinolopha) predominantly have small horns on their snouts between their eyes and their nostrils, whereas others do not.
Senses Green iguanas have excellent vision, enabling them to detect shapes and motions at long distances. As green iguanas have only a few rod cells, they have poor vision in low-light conditions. At the same time, they have cells called double-cone cells that give them sharp color vision and enable them to see ultraviolet wavelengths. This ability is highly useful when basking so they can ensure they absorb enough sunlight to produce vitamin D.
Green iguanas have a white photosensory organ on the top of their heads called the parietal eye (also called the third eye, pineal eye, or pineal gland), in contrast to most other lizards that have lost this primitive feature. This "eye" has only a rudimentary retina and lens and cannot form images, but is sensitive to changes in light and dark and can detect movement. This helps the iguana detect predators stalking it from above.
Ecology
Reproductive biology
Male green iguanas have highly developed femoral pores on the underside of their thighs, which secrete a scent (females have femoral pores, but they are smaller in comparison to those of the males). In addition, the dorsal spines that run along a green iguana's back are noticeably longer and thicker in males than they are in females, making the animals somewhat sexually dimorphic.
Male green iguanas tend to display more dominant behaviors, such as head bobbing and tail whipping. They also tend to develop a taller dorsal crest than females, as well as taller dorsal spines (or spikes). Large, round, very pronounced jowls are generally a male characteristic. Jowls are located under the jaw and are protected by the subtympanic plate, which is a large, green, circular-shaped scale.
Green iguanas are oviparous, with females laying clutches of 20 to 71 eggs once per year during a synchronized nesting period. The female green iguana gives no parental protection after egg laying, apart from defending the nesting burrow during excavation. In Panama, the green iguana has been observed sharing nest sites with American crocodiles, and in Honduras with spectacled caimans.
The hatchlings emerge from the nest after 10–15 weeks of incubation. Once hatched, the young iguanas look similar to the adults in color and shape, resembling adult females more so than males and lacking dorsal spines.
Juveniles stay in familial groups for the first year of their lives. Male green iguanas in these groups often use their own bodies to shield and protect females from predators, and it appears to be the only species of reptile to do this.
Behavior
Green iguanas are diurnal, arboreal, and are often found near water. Agile climbers, Iguana iguana can fall up to and land unhurt (iguanas use their hind leg claws to clasp leaves and branches to break a fall). During cold, wet weather, green iguanas prefer to stay on the ground for greater warmth. When swimming, iguanas remain submerged, letting their legs hang limply against their sides. They propel through the water with powerful tail strokes.
While they may often be found in trees, these animals are well-known burrowers. The size of their burrow can range from deep, with a diameter of . They have been observed burrowing in canals, levees, and dikes and along seawalls in southern Florida. If individuals do not dig their own, they may even use gopher tortoise burrows or usurp those of the Florida burrowing owl.