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Green Iguana

The green iguana or common iguana (Iguana iguana) is a large, arboreal herbivorous species of lizard of the genus Iguana native to Central and South America. The green iguana ranges over a large geographic area, from southern Brazil and Paraguay to as far north as Mexico, the Caribbean Islands; and in the United States as feral populations in South Florida (including the Florida Keys), Hawaii and the Rio Grande Valley of Texas.

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 .

Commonly found in captivity as a pet due to its calm disposition and bright colors, it can be demanding to care for properly. Space requirements and the need for special lighting and heat can prove challenging to an amateur hobbyist.

Taxonomy and etymology

The species was first officially described by Swedish botanist Carolus Linnaeus in 1758. In the two centuries since then, no less than 17 species and subspecies have been identified with all but one species (Iguana delicatissima) being found to be invalid.

Using nuclear and mitochondrial DNA-sequence data to explore the phylogenic history of the green iguana, scientists from Utah Valley State College studied animals collected from 17 different 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.

The word iguana is derived from a Spanish form of the Taino name for the species: iwana. In Spanish speaking countries, males of the species are referred to as gorrobo or ministro and juveniles are called iguanita or gorrobito.

Distribution and habitat

The native range of the green iguana extends from southern Mexico to central Brazil, Paraguay, and Bolivia and the Caribbean; specifically Grenada, Curaçao, Trinidad and Tobago, St. Lucia, St. Vincent, and Utila. They have been introduced to Grand Cayman, Puerto Rico, Texas, Florida, Hawaii, and the US Virgin Islands.

Green iguanas are diurnal and arboreal and 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, an iguana remains submerged, letting its four legs hang limply against its side. They propel through the water with powerful tail strokes.

Because of the green iguana's popularity in the pet trade and as a food source in Latin America, they are listed on the CITES Appendix II, which means that while they are not an endangered species, "their trade must be controlled so as to not harm the species in the future".

Anatomy and morphology

In southern countries of their range, such as Peru, green iguanas appear bluish in color with bold black markings. On islands such as Bonaire, Curacao, Aruba, and Grenada, a Green iguana's color may range from green to lavender, black, and even pink. 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 as babies, however they lose this color as they get older.

Iguana iguana possess a row of spines along their backs and along their 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, the iguana can allow it to break, so it can escape and eventually regenerate a new one. In addition, iguanas have well developed dewlaps which helps regulate their body temperature. It is also used in courtships and displays.

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 the animal can ensure that it absorbs enough sunlight in the forms of UVA and UVB to produce Vitamin D.

Green iguanas have a white photosensory organ on the top of their heads called the parietal eye (also called third eye, pineal eye or pineal gland), in contrast to most other lizards, which have lost it. This "eye" does not function the same way as a normal eye does, as it has only a rudimentary retina and lens and cannot form images. It is, however, sensitive to changes in light and dark and can detect movement. This helps the iguana when being stalked by predators from above.

I. iguana 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 Iguanadon, 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 nutritional content per gram, 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 chloride.

Green iguanas from Guatemala and southern Mexico predominantly have small horns on their snouts between their eyes and their nostrils, whereas others do not. Naturalists once classified these iguanas as a separate subspecies (Iguana iguana rhinolopha); however, this classification has been found to be invalid based on mitochondrial DNA and iguanas with similar nose projections appear randomly in other populations and interbreed freely with those that do not share this trait.

Sex preferences and actions

Male green iguanas have highly developed femoral pores on the underside of their thighs which secrete a scent (females also 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.

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 which does this.

Behavior

When frightened by a predator, green iguanas will attempt to flee, and if near a body of water, dive into it and swim away. If cornered by a threat, the green iguana will extend and display the dewlap under its neck, stiffen and puff up its body, hiss, and bob its head at the aggressor. If the threat persists Iguana iguana can lash with its tail, bite and use its claws in defense. The wounded are more inclined to fight than uninjured prey.

Green iguanas use "head bobs" and dewlaps in a variety of ways in social interactions, such as greeting another iguana or to court a possible mate. The frequency and number of head bobs have particular meanings to other iguanas.

Green iguanas are preyed upon by hawks and their fear of hawks is exploited as a ploy to catch them in the wild. The sound of a hawk's whistle or scream makes the iguana freeze and it becomes easier to capture.

Diet

Green iguanas are primarily herbivores, feeding on leaves, flowers, fruit, and growing shoots of upwards of 100 different species of plant. In Panama one of the green iguana's favorite foods is wild plum, Spondias monbin.

Although they will consume a wide variety of foods if offered, green iguanas are naturally herbivorous and require a precise ratio of minerals (2 to 1 calcium to phosphorus) in their diet. Juvenile iguanas tend to be insectivores and often eat feces from adults in order to acquire the essential microflora to digest their low-quality and hard to process diet.

There is some debate as to whether captive green iguanas should be fed animal protein. There is evidence of wild iguanas eating grasshoppers and tree snails, usually as a byproduct of eating plant material. Wild adult Green iguanas have also been observed eating bird's eggs. Zoologists, such as Adam Britton, believe that such a diet containing protein is unhealthy for the animal's digestive system resulting in severe long-term health damage including kidney failure and leading to premature death. On the other side of the argument is that green iguanas at the Miami Seaquarium in Key Biscayne, Florida, have been observed eating dead fish and individuals kept in captivity have been known to eat mice without any ill effects. De Vosjoli also writes that captive animals have been known to survive and thrive on eating nothing but whole rodent block, or monkey chow, and one instance of Romaine lettuce with vitamin and calcium supplements.

Captivity

The American pet trade has put a great demand on the green iguana; 800,000 iguanas were imported into the U.S. in 1995 alone, primarily originating from captive farming operations based in their native countries (Honduras, El Salvador, Colombia, and Panama). However, these animals are demanding to care for properly over their lifetime, and many die within a few years of acquisition.

Although, in captivity, green iguanas will eat meat if presented with it, excessive consumption of animal protein results in severe kidney problems and possible premature death. Misinformed pet owners tend to feed iguanas iceberg lettuce, which provides iguanas with water but has no other nutritional value. A captive Green iguana's diet should consist of fresh leafy vegetables such as mustard greens, collard greens, dandelion, arugula or kale and access to fresh water.

Green iguanas will thrive only in temperatures of to and must have appropriate sources of UVB and UVA lighting, or else their bodies cannot produce vitamin D that promotes calcium absorption, which can result in a metabolic bone disease that can be fatal. In some locales(New York City and Hawaii), iguanas are considered exotic pets, and are prohibited from ownership. Hawaii has strict regulations regarding the import and possession of Green iguanas, violators can spend three years in jail and fined up to $200,000. This is due to the potential impact of an introduced species on Hawaii's ecosystem.

As an invasive species

Due to a combination of events, the green iguana is considered an invasive species in South Florida and is found along the gulf coast of Florida from Key West to Pinellas County. The original small populations in the Florida Keys were animals that had arrived there due to hurricanes and storms; others were stowaways on ships carrying fruit from South America. Over the years, other iguanas were introduced into the wild mostly originating through the pet trade. Some were escapees and some were intentionally released by their owners, these iguanas survived and then thrived in their new habitat. They commonly hide in the attics of houses and on beaches. They often destroy gardens and landscaping. However, they seem to be fond of eating a native endangered plant, Cordia globosa and feeding on Nicker nut (Caesalpinia) a primary food plant of the endangered Miami Blue Butterfly (Cyclargus thomasi bethunebakeri); additionally on Marco Island, green iguanas have been observed using the burrows of the Florida Burrowing Owl, a species of special concern, all of which can make them more of a serious threat to Florida's ecosystem than originally believed.

In January of 2008, large numbers of feral iguanas in Florida dropped from the trees in which they lived, due to uncommonly cold nights causing their metabolisms to go into a "state of suspended animation" in which they lost their grips on the tree branches. Though no specific numbers were provided by local wildlife officials, local media described the phenomenon as a "frozen iguana shower" in which dozens "littered" local bike paths. Upon the return of daytime warmth many (but not all) of the iguanas "woke up" and resumed their normal activities. The green iguana is established in Maui, Hawaii as a feral species (despite strict legislation)and the Rio Grande Valley of Texas. As most reptiles carry salmonella, this is also a concern and a reason legislation has been sought to regulate the trade in Green iguanas.

In the aftermath of two Caribbean hurricanes in 1995 , a group of fifteen green iguanas was found to be living on Anguilla; an island where that species have never been recorded previously. Biologist Ellen Censky, of the Connecticut State Museum of Natural History, believes that the new iguanas had accidentally gotten caught on the trees and rafted two hundred miles across the ocean from Guadaloupe, where green iguanas are an indigenous species. By examining the weather patterns and ocean currents, Censky has shown that the iguanas had spent three weeks at sea before arriving on the island. This colony began breeding on the new island within two years of its arrival.

Cultural references

The Moche people of ancient Peru worshipped animals and often depicted Green iguanas in their art. The Green iguana and its relative the Black iguana (Ctenosaura similis) have been used as a food source in Central and South America for the past 7000 years. It is possible that some of the populations in the Caribbean were translocated there from the mainland by various tribes as a food source. In Central and South America, Green iguanas are still used as a source of meat and are often referred to as gallina de palo, "bamboo chicken" or "chicken of the tree," because they are said to taste like chicken.

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