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Iguana iguanaCommon Green Iguana

By Fred Gingell

Geographic Range

Green iguanas, Iguana iguana, occur throughout Central and South America, from Sinaloa and Veracruz, Mexico, south to the Tropic of Capricorn in Paraguay and southeast Brazil. This large lizard also inhabits many islands throughout the Caribbean region and the coastal eastern Pacific, and has been introduced into southern Florida and in Hawaii. This is the largest known lizard to occur within the borders of the United States (Conant and Collins, 1998; Campbell, 1998). (Campbell, 1998; Conant and Collins, 1998)

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 (Conant and Collins 1998). (Alberts, et al., 2004; Campbell, 1998; Conant and Collins, 1998)

Physical Description

Within three years, a young, 12 gram hatchling iguana can become a 1 kg adult (de Vosjoli, 1992). 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. (De Vosjoli, 1992; Frye, 1995; Oldham and Smith, 1975)

  • Sexual Dimorphism
  • male larger
  • sexes colored or patterned differently
  • male more colorful
  • ornamentation
  • Range mass
    4 to 8 kg
    8.81 to 17.62 lb
  • Average mass
    7 kg
    15.42 lb
  • Range length
    2 (high) m
    6.56 (high) ft
  • Average length
    1.75 m
    5.74 ft

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. (Frye, 1995; Kaplan, 2002)

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 (Frye, 1995). Dominant males may also mark rocks, branches, and females with a waxy pheromone-containing substance secreted from their femoral pores.

During mating, the male approachs 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 can save sperm for several years (Frye, 1995), allowing them to fertilize eggs at a much later date. (De Vosjoli, 1992; Frye, 1995)

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.

Timing of sexual maturity varies. Animals may be able to breed as early as their second year, but may not breed until as late as their fifth year. (Frye, 1995)

  • Breeding interval
    These animals breed annually.
  • Breeding season
    Green iguanas breed in the dry season.
  • Range number of offspring
    65 (high)
  • Average number of offspring
    10-30
  • Range gestation period
    59 to 84 days
  • Average gestation period
    65 days
  • Range age at sexual or reproductive maturity (female)
    2.5 to 5 years
  • Average age at sexual or reproductive maturity (female)
    3-4 years
  • Range age at sexual or reproductive maturity (male)
    3 to 5 years

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. (De Vosjoli, 1992)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • male
      • female

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. (De Vosjoli, 1992; Frye, 1995)

  • Range lifespan
    Status: captivity
    20 (high) years
  • Average lifespan
    Status: wild
    8 years
  • Average lifespan
    Status: captivity
    10 years
  • Average lifespan
    Sex: female
    Status: captivity
    12.4 years
    Max Planck Institute for Demographic Research

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 (Alberts et. al., 2004).

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 autotomatize, 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 autotomatized spot and regrow with in a year, though not to the length it was before. (Alberts, et al., 2004)

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 (Alberts et.al., 2004). 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. (Alberts, et al., 2004; Frye, 1995)

  • Animal Foods
  • eggs
  • insects
  • terrestrial worms
  • Plant Foods
  • leaves
  • fruit
  • flowers

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.

  • Anti-predator Adaptations
  • cryptic

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. (Kaplan, 2002; Phillips, 1990)

  • Ecosystem Impact
  • disperses seeds

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. (Campbell, 1998). (Campbell, 1998)

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.

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Fred Gingell (author), Michigan State University, James Harding (editor, instructor), Michigan State University.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

arboreal

Referring to an animal that lives in trees; tree-climbing.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

food

A substance that provides both nutrients and energy to a living thing.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

frugivore

an animal that mainly eats fruit

herbivore

An animal that eats mainly plants or parts of plants.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

mimicry

imitates a communication signal or appearance of another kind of organism

native range

the area in which the animal is naturally found, the region in which it is endemic.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

sexual ornamentation

one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs.

solitary

lives alone

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

suburban

living in residential areas on the outskirts of large cities or towns.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

References

Alberts, A., R. Carter, W. Hayes, E. Martins. 2004. Iguanas: Biology and Conservation. Berkeley and Los Angeles, Californa: University of California Press.

Campbell, J. 1998. Amphibians and Reptiles of Norther Guatemala,the Yucatan, and Belize. Oklahoma: University of Oklahoma Press.

Conant, R., J. Collins. 1998. Peterson Field Guides: Reptiles and Amphibians of Eastern & Central North America, 3rd Edition. New York: Houghton Mifflin Company.

De Vosjoli, P. 1992. The Green Iguana Mannual. Lakeside, California: Advanced Vivarium Systems.

Frye, F. 1995. Iguana Iguana, Guide for Successful Captive Care. Malabar, Florida: Krieger Publishing Company.

Kaplan, M. 2002. "Journal Abstracts: Iguana iguana Visual and Chemical Reception" (On-line). Accessed July 14, 2005 at http://www.anapsid.org/iguana/sight2.html.

Oldham, J., H. Smith. 1975. Laboratory Anatomy of the Iguana. Dubuque, Iowa: WM. C. Brown Company.

Phillips, J. 1990. Iguana iguana: a model species for studying the ontogeny of behavior/hormone interactions. Exp Zool Suppl, 4: 167-169. Accessed January 03, 2005 at http://www.anapsid.org/iguana/sight2.html.

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