Iguana iguana (Linnaeus, 1758)

• Habitat
• Physical Description
• Development
• Reproduction
• Lifespan/Longevity

• Behavior
• Communication and Perception
• Food Habits
• Predation
• Ecosystem Roles
• Economic Importance for Humans: Positive

• Economic Importance for Humans: Negative
• Conservation Status

Habi­tat

Green Igua­nas are ar­bo­real lizards that live high in the tree canopy. Ju­ve­niles es­tab­lish areas lower in the canopies while older ma­ture igua­nas re­side higher up. This tree dwelling habit al­lows them to bask in the sun, rarely com­ing down ex­cept when fe­males dig bur­rows to lay eggs. Al­though pre­fer­ring an ar­bo­real (forested) en­vi­ron­ment, they can ad­just well to a more open area. No mat­ter where they in­habit, they pre­fer to have water around as they are ex­cel­lent swim­mers and will dive be­neath the water to avoid preda­tors.

Phys­i­cal De­scrip­tion

Within three years, a young, 12 gram hatch­ling iguana can be­come a 1 kg adult . Upon hatch­ing, the length of green igua­nas ranges from 17 to 25 cm. Most ma­ture igua­nas weigh be­tween 4 and 6 kg, but some in South Amer­ica, with proper diet can reach up to 8 kg. These large lizards can reach head to tail lengths of around 2 m.

Al­though called green igua­nas, these an­i­mals are ac­tu­ally vari­able in color. The adults be­come more uni­form in color with age, whereas the young may ap­pear more blotchy or banded be­tween green and brown. Color of an in­di­vid­ual may also vary based upon its mood, tem­per­a­ture, health, or so­cial sta­tus. Such color al­ter­ation may aide these an­i­mals in ther­moreg­u­la­tion. In the morn­ing, while body tem­per­a­ture is low, skin color will be darker, help­ing the lizard to ab­sorb heat from sun­light. How­ever, as the hot mid-day sun ra­di­ates upon them, these an­i­mals be­come lighter or paler, help­ing to re­flect the sun rays and min­i­miz­ing the heat ab­sorbed. Ac­tive dom­i­nant igua­nas usu­ally have a darker color than lower-ranked igua­nas liv­ing the same en­vi­ron­ment (Frye, 1995). Most color vari­a­tion seen in this species is ex­hib­ited by males, and may be at­trib­uted in part to sex steroids. Six to eight weeks prior to and dur­ing courtship, males may ac­quire a bright or­ange or gold hue, al­though col­oration is still re­lated to dom­i­nance sta­tus (Frye, 1995). Ma­ture fe­males, for the most part, re­tain their green col­or­ing.

Other dis­tin­guish­ing fea­tures of this species in­clude a pen­du­lous dewlap under the throat, a dor­sal crest made up of der­mal spines that run from the mid neck to the tail base, and a long ta­per­ing tail. The dewlap is more de­vel­oped in adult males than fe­males. Ex­ten­sions of the hyoid bones stiffen and sup­port the lead­ing edge of this struc­ture, which is used in ter­ri­to­r­ial de­fense or when the an­i­mal is fright­ened. This fleshy struc­ture also serves in heat ab­sorp­tion and dis­si­pa­tion when it is ex­tended.

The lat­er­ally sit­u­ated eyes are pro­tected mainly by a im­mov­able eye­lid and freely mo­bile lower eye­lid (Old­ham and Smith, 1975). On the dor­sal mid­line of the skull be­hind the eyes is a pari­etal eye. This sense organ, al­though not a true “eye,” serves as a meter for solar en­ergy, and aids in the mat­u­ra­tion of sex or­gans, thy­roid gland, and en­docrine glands (Frye, 1995). The vi­sual ef­fect of this “eye” is mostly lim­ited to the de­tec­tion of preda­tory shad­ows from above.

The scales or plates on the head are larger and more ir­reg­u­lar than the scales on the rest of the body. Below the tym­pa­num there is a large rounded scale called the sub­tym­panic plate.

De­vel­op­ment

Ap­prox­i­mately 65 days after mat­ing, a fe­male is ready to lay her eggs. The size and num­ber of eggs pro­duced varies de­pend­ing upon her size, her nu­tri­tional sta­tus, and her ma­tu­rity. Eggs mea­sure around 15.4 mm in di­am­e­ter, and 35 to 40 mm in length (Frye, 1995). Over a three day pe­riod, an av­er­age of 10 to 30 leath­ery white or pale-cream col­ored eggs are de­posited into a nest. Nests are lo­cated 45 cm to more than a meter deep, and may be shared with other fe­males if nest­ing areas are lim­ited. After lay­ing the eggs, fe­males may re­turn to the nest sev­eral times but do not stay to guard it.

In­cu­ba­tion lasts from 90 to 120 days. Tem­per­a­ture should range from 85 to 91 de­grees Fahren­heit. The hatch­lings pip the egg open using a spe­cial egg tooth, called the carun­cle, that falls off shortly after hatch­ing. Ab­sorbed yolk pro­vides most of the nour­ish­ment for the first week or two of an iguana’s life.

There are no major mor­pho­log­i­cal changes in these an­i­mals as they age, ex­cept that they grow. How­ever, diet is re­lated to age. The young, with higher need for pro­tein, are more likely to con­sume in­sects and eggs than are ma­ture in­di­vid­u­als.

Re­pro­duc­tion

Most green igua­nas reach sex­ual ma­tu­rity be­tween three and four years of age, al­though ma­tu­rity can be reached ear­lier. Igua­nas tend to breed in the dry sea­son, en­sur­ing that young hatch in the wet sea­son when food is more read­ily avail­able (de Vosjoli, 1992).

Mat­ing ap­pears to be polyg­y­nan­drous. Courtship oc­curs within a de­fined ter­ri­tory where more than one fe­male may be pre­sent. Con­flicts be­tween males are not un­com­mon. Courtship be­hav­ior of males in­cludes head bob­bing, ex­tend­ing and re­trac­tion of the dewlap, and nuz­zling or bit­ing a fe­male’s neck. Dom­i­nant males may also mark rocks, branches, and fe­males with a waxy pheromone-con­tain­ing sub­stance se­creted from their femoral pores.

Dur­ing mat­ing, the male approaches the fe­male and climbs on her back, strad­dling her. To re­strain his mate, he grips the her shoul­der skin with his teeth, some­times caus­ing wounds. The male then pairs his cloa­cal vent up with the fe­male’s and in­serts one of his hemipenes into her cloaca. Cop­u­la­tion can last for sev­eral min­utes. Fe­male igua­nas can save sperm for sev­eral years, al­low­ing them to fer­til­ize eggs at a much later date.

Fe­males lay their eggs about 65 days after mat­ing (eggs take 59 to 84 days to de­velop be­fore they are laid). Over the course of three days, fe­males may up to 65 eggs, each mea­sur­ing around 15.4 mm in di­am­e­ter, and 35 to 40 mm in length (Frye, 1995). Eggs are de­posited into nests which are lo­cated 45 cm to more than a meter deep, and may be shared with other fe­males if nest­ing areas are lim­ited.

In­cu­ba­tion lasts from 90 to 120 days. Tem­per­a­ture should range from 85 to 91 de­grees Fahren­heit. The hatch­lings pip the egg open using a spe­cial egg tooth, called the carun­cle, that falls off shortly after hatch­ing. Ab­sorbed yolk pro­vides most of the nour­ish­ment for the first week or two of an iguana’s life. Young are in­de­pen­dent from birth.

Parental in­vest­ment in­cludes the risk of mat­ing and lay­ing eggs. Eggs are pro­vi­sioned with nu­tri­ents by the mother. Fe­males choose nest­ing sites, pre­sum­ably as a means of car­ing for their off­spring. How­ever, after eggs are laid, there is no di­rect in­vest­ment in the young.

Lifes­pan/Longevity

Igua­nas can live for more than 20 years in cap­tiv­ity, al­though wild igua­nas are thought to live only about 8 years. Proper nu­tri­tion for growth is a con­cern for cap­tive man­age­ment of these an­i­mals. Im­proper hous­ing and nu­tri­tion can shorten a cap­tive iguana’s lifes­pan.

Be­hav­ior

In the wild, most dis­putes be­tween igua­nas take place over bask­ing sites. There is usu­ally ad­e­quate food for these her­biv­o­rous lizards, but good perches are lim­ited. Bask­ing is im­por­tant for in­creas­ing body tem­per­a­ture and aid­ing di­ges­tion.

Dur­ing the breed­ing sea­son, males be­come ter­ri­to­r­ial and dis­play head bob­bing, dewlap ex­ten­sion, and color changes. They will bite at each other. In­juries in the wild are rare, as there is ample space for males to re­treat when threat­ened. How­ever, in cap­tiv­ity where space is lim­ited, in­juries are more com­mon. Fe­males may also dis­play some of these be­hav­iors when nest­ing sites are lim­ited.

Green igua­nas may travel con­sid­er­able dis­tances in sev­eral cases. Fe­males mi­grate to the same nest­ing site for sev­eral years in a row, then travel back to their home ter­ri­tory once their eggs are laid. Hatch­lings may dis­perse over large dis­tances as well.

When fright­ened, an iguana will usu­ally freeze or hide. If caught, twist­ing and ro­tat­ing around or tail whip­ping may occur. Like many other lizards, igua­nas can automatize, or drop of part of their tail. This gives them a chance to es­cape be­fore their preda­tor fig­ures out what is going on. A new tail will sprout from the automatized spot and re­grow with in a year, though not to the length it was be­fore.

Com­mu­ni­ca­tion and Per­cep­tion

These an­i­mals are known to use vi­sual sig­nals, such as head bob­bing and dewlap ex­ten­sion, as means of com­mu­ni­cat­ing with ri­vals. In ex­treme cases, phys­i­cal con­tact is in­volved in al­ter­ca­tions. In ad­di­tion, males scent mark fe­males as well as branches. Hiss­ing, which is a form of au­di­tory com­mu­ni­ca­tion, some­times oc­curs.

Food Habits

Green igua­nas are pri­mar­ily her­biv­o­rous. They oc­ca­sion­ally eat a small amount of car­rion or in­ver­te­brates. Green leafy plants or ripe fruits are their pre­ferred foods.

Green igua­nas use their tongues to help ma­nip­u­late the food and bite small enough pieces to swal­low, with lit­tle or no chew­ing. The food mixes with en­zymes in the stom­ach be­fore mov­ing to the small in­tes­tine where pan­cre­atic en­zymes and bile are mixed with it. Most di­ges­tion oc­curs in the sac­cu­lated colon, where mi­croflora break down the cel­lu­lose (Frye, 1995). Mi­croflora are es­sen­tial for hind-gut di­ges­tion of the hard to di­gest diet of this species. Hatch­ling igua­nas are in­clined to eat feces from adults, which may be an adap­ta­tion for ac­quir­ing this much need mi­croflora. This mi­croflora breaks the food down and makes it avail­able for ab­sorp­tion.

Igua­nas re­quire a high amount of di­etary pro­tein in their first two to three years for ad­e­quately fast growth. Dur­ing this time pe­riod, young igua­nas may con­sume in­sects and spi­ders. Older igua­nas that have reached close to max­i­mum growth con­sume a low phos­pho­rous, high cal­cium, leafy diet for their main­te­nance re­quire­ments.

Igua­nas are ec­tother­mic. Their body tem­per­a­ture is mainly de­pen­dent upon the en­vi­ron­men­tal tem­per­a­ture. Low en­vi­ron­men­tal tem­per­a­tures in­hibit an iguana’s ap­petite and di­ges­tive en­zymes. Ac­tive eat­ing usu­ally oc­curs when the en­vi­ron­men­tal tem­per­a­tures are be­tween 77 and 95 de­grees Fahren­heit (Frye, 1995). Bask­ing is an im­por­tant aid to di­ges­tion. Igua­nas may cease eat­ing prior to or dur­ing skin shed­ding. Fe­males may refuse to eat dur­ing later stages of egg de­vel­op­ment. In­di­vid­u­als who are overly stressed or in a new en­vi­ron­ment may also refuse to eat.

Pre­da­tion

One of the best meth­ods for igua­nas to avoid pre­da­tion is their cryp­tic col­oration. Be­cause they look like so much of their green en­vi­ron­ment, they can re­main im­mo­bile when a preda­tor has been spot­ted, and go un­no­ticed them­selves. Young igua­nas may be found in small groups, and use the “self­ish-herd” or “more eyes are bet­ter” strat­egy to avoid preda­tors. Igua­nas pre­fer to bask in tree limbs that over-hang water so when threat­ened by a preda­tor they can dive into the water and swim swiftly away. In ad­di­tion to these strate­gies for avoid­ing pre­da­tion, green igua­nas are able to shed a large por­tion of their tail, thus dis­tract­ing preda­tors and al­low­ing the “rest” of the an­i­mal to es­cape.

Hawks and other large birds are po­ten­tial preda­tors of ju­ve­nile igua­nas. Hu­mans are an­other one of major preda­tors of green igua­nas. Hu­mans eat both igua­nas and their eggs. Hu­mans also use these rep­tiles for croc­o­dile bait, and poach them for the pet trade.

Like many other an­i­mals, green igua­nas also suf­fer from habi­tat de­struc­tion.

Ecosys­tem Roles

In ad­di­tion to help­ing dis­perse seeds, igua­nas pro­vide a source of food for larger preda­tory an­i­mals, in­clud­ing hu­mans. Like other am­phib­ians and rep­tiles, igua­nas can be in­di­ca­tors of en­vi­ron­men­tal changes (Ka­plan, 2002). Rep­tiles are more sen­si­tive to en­vi­ron­men­tal changes than are hu­mans, and by watch­ing their re­sponses, we can be alerted to pos­si­ble prob­lems be­fore they are large enough for us to de­tect with our own senses.

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Igua­nas are farmed in some coun­tries as a source of food and leather, as well as for the pet trade. Due to their large size, iguana hides pro­vide a source of lux­ury leather that can be made into boots, belts or purses. The pet in­dus­try also prizes igua­nas; most are sold in the United States, Eu­rope, and Japan. Igua­nas also make an in­ter­est­ing tourist at­trac­tion in re­sort areas.

Ex­ploita­tion of igua­nas has re­sulted in marked de­clines in their num­bers in some parts of their range.

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

The most ad­verse ef­fect green igua­nas have on hu­mans would be eat­ing ex­otic trop­i­cal fo­liage in gar­dens. They do not pose any major prob­lems for hu­mans.

Con­ser­va­tion Sta­tus

Al­though some pop­u­la­tions have suf­fered from poach­ing and col­lec­tion for the pet trade, green igua­nas are not con­sid­ered a con­ser­va­tion risk at this time. All Iguana species are listed under CITES Ap­pen­dix II.