The Green Iguana

Nov 10, 2013 Features / Columnists, Interesting Creatures in Guyana

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The green iguana or common iguana (Iguana iguana) is a large, arboreal, mostly herbivorous species of lizard of the genus Iguana native to Central, South America, and the Caribbean. Usually, this animal is simply called the iguana. The green iguana ranges over a large geographic area, from southern Brazil and Paraguay as far north as Mexico and the Caribbean Islands.
As a herbivore it has adapted significantly with regard to locomotion and osmoregulation as a result of its diet. It grows to 1.5 metres (4.9 ft) in length from head to tail, although a few specimens have grown more than 2 metres (6.6 ft) with bodyweights upward of 20 pounds (9.1 kg).

Commonly found in captivity as a pet due to its calm disposition and bright colours, it can be very demanding to care for properly. Space requirements and the need for special lighting and heat can prove challenging to an amateur hobbyist.
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”.
The Iguanas are often referred to as “Disposable Pets” due to owners not taking proper care of them and later disposing of them.
Despite their name, Green Iguanas can come in different colours. In southern countries of their range, such as Peru, green iguanas appear bluish in colour with bold blue markings. Green Iguanas 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 help regulate their body temperature. This dewlap is used in courtships and territorial displays.
Green Iguanas have excellent vision, enabling them to detect shapes and motions at long distances. However, because they only have 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 colour 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 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.
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 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 waste 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.
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.
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.
The hatchlings emerge from the nest after 10–15 weeks of incubation. Once hatched, the young iguanas look similar to the adults in colour 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.
When frightened by a predator, Green Iguanas will attempt to flee, and if near a body of water, they 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, the Iguana can lash with its tail, bite and use its claws in defence. 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 hunted by predatory birds and their fear of these 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.
Green Iguanas are primarily herbivores, feeding on leaves, flowers, fruit, and growing shoots of upwards of 100 different species of plant.  It is important for captive iguanas to have a variety of leafy greens along with fruits and vegetables such as turnip greens, collards, butternut squash, acorn squash, mango, and parsnip.
Juvenile iguanas often eat faeces from adults in order to acquire the essential microflora to digest their low-quality and hard to process vegetarian only diet.
(Source: Wikipedia – The Free Online Encyclopedia)

 

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