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''Iguana'' (, ) is a genus of herbivorous
lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...
s that are native to tropical areas of Mexico, Central America, South America, and the
Caribbean The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both the Caribbean Se ...
. The genus was first described in 1768 by Austrian naturalist Josephus Nicolaus Laurenti in his book ''Specimen Medicum, Exhibens Synopsin Reptilium Emendatam cum Experimentis circa Venena''. Two species are placed in the genus, the green iguana, which is widespread throughout its range and a popular pet, and the Lesser Antillean iguana, which is native to the Lesser Antilles. Genetic analysis indicates that the green iguana may comprise a complex of multiple species, some of which have been recently described, but the Reptile Database considers all of these as subspecies of the green iguana. The word "iguana" is derived from the original Taino name for the species, ''iwana''. In addition to the two species in the genus ''Iguana'', several other related genera in the same family have common names of the species including the word "iguana". The species is a popular quarry for pets, and has been widely introduced beyond its native area, into Ishigaki Island, Florida Peninsula, Hawaii, numerous islands in the Lesser Antilles, Singapore, Thailand, and Taiwan.


Anatomy and physiology

Iguanas can range from in length, including their tails. These
lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...
s possess a dewlap and a row of elongated scales running from the midline of their
neck The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...
s down to their tails. Iguanas have varying types of scales covering different areas of their body, for example, some large, round tuberculate scales are scattered around the lateral region of the neck among smaller, overlapping scales. The scales on the dorsal trunk of their bodies are also thicker and more tightly packed than those on the ventral sides. These scales may be a variety of colors and are not always visible from close distances. They have a large, round scale on their cheeks known as a subtympanic shield. Iguanas have keen vision and can see shapes, shadows, colors, and movement at long distances. Their visual acuity enables them to navigate through crowded forests and to locate food. They employ visual signals to communicate with other members of the same species. The tympanum, the iguana's
eardrum In the anatomy of humans and various other tetrapods, the eardrum, also called the tympanic membrane or myringa, is a thin, cone-shaped membrane that separates the external ear The outer ear, external ear, or auris externa is the extern ...
, is located above the subtympanic shield (or "ear shield") behind each eye. Iguanas are often hard to spot, as they tend to blend into their surroundings, and their coloration enables them to hide from larger predators. Like most
reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...
s, an iguana has a three-chambered heart with two atria, one ventricle, and two aortae with a
systemic circulation The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
. The muscles of an iguana are very light in color due to the high proportion of fast-twitch, glycolytic muscle fibers (type A). These A fibers are not very vascularized and are low in
myoglobin Myoglobin (symbol Mb or MB) is an iron- and oxygen-binding protein found in the cardiac and skeletal muscle tissue of vertebrates in general and in almost all mammals. Myoglobin is distantly related to hemoglobin. Compared to hemoglobin, myoglobi ...
, giving them their pale look. This high density of A fibers allows iguanas to move very quickly for a short period of time, which facilitates short bursts of movement, but is inefficient for long duration movement, since cellular respiration in A fibers is anaerobic.


Parietal eye

Several species of lizards, including the iguanas, have a pale scale towards the back of their heads marking the parietal eye. This organ is sensitive to changes in illumination and sends signals to the
pineal gland The pineal gland, conarium, or epiphysis cerebri, is a small endocrine gland in the brain of most vertebrates. The pineal gland produces melatonin, a serotonin-derived hormone which modulates sleep, sleep patterns in both circadian rhythm, circ ...
noting the change between day and night. A photopigment commonly found in the lamprey, known as parapinopsin, is also found in the iguana, and is sensitive to ultraviolet light and aids in the signaling between day and night.


Skull morphology and diet

Iguanas have developed an herbivorous lifestyle, foraging exclusively on vegetation and foliage. To acquire, process, and digest plant matter, herbivorous lizards must have a higher bite force relative to their size in comparison to
carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...
or omnivorous reptiles. The skull of the iguana has undergone modifications resulting in a strong bite force and efficient processing of vegetation, according to one study. To accomplish this
biomechanically Biomechanics is the study of the structure, function and motion of the mechanical aspects of biological systems, at any level from whole organisms to organs, cells and cell organelles, using the methods of mechanics. Biomechanics is a branch of ...
, herbivorous lizards have taller and wider skulls, shorter snouts, and larger bodies relative to carnivorous and omnivorous reptiles. Increasing the strength of the skull allows for increased muscle presence and increases the ability of the skull to withstand stronger forces. Furthermore, the teeth of the iguana are acrodontal, meaning that their teeth sit on top of the surface of the jaw bone and project upwards. The teeth themselves are small and serrated - designed to grasp and shear food.


Reproduction

Male iguanas, like other male examples of Squamata, have two
hemipenes A hemipenis (plural hemipenes) is one of a pair of intromittent organs of male squamata, squamates (snakes, lizards and amphisbaenia, worm lizards). Hemipenes are usually held inverted within the body, and are everted for reproduction via erecti ...
. During copulation, one hemipenis is inserted into the female's cloacal vent. A female can store sperm from previous mates for several years to continue to fertilize her eggs in case she finds no male within her territory when she is ready to lay again.


Mating/courtship

Iguanas tend to follow a promiscuous or
polygynadrous Polygynandry is a mating system in which both males and females have multiple mating partners during a breeding season. In sexually reproducing diploid animals, different mating strategies are employed by males and females, because the cost of ga ...
mating style during the dry season. Mating during the dry season ensures that their offspring will hatch during the wet or rainy season when food will be more plentiful. Females control large territories, where they make several nests. Males compete for the females in an area and mark their won territory with a pheromone secreted from the femoral pores on the dorsal side of their hind limbs. Male behavior during sexual competition involves head bobbing, extending and retracting their dewlap, nuzzling and biting the necks of females, and on occasion, changing color. Once a female chooses a male, he straddles the female and holds her in place by biting onto her shoulder, which sometimes leaves scars on females. After copulation, eggs are laid within several nests and allowed to incubate. This low level of parental intervention with their offspring makes iguanas an example of r-strategy reproduction.


Phylogeny

A phylogeny based on nuclear protein-coding genes, reviewed by Vidal and Hedges (2009), suggested that the subclade Iguania is in a group with snakes and anguimorphs (lizards). These groups share an oral gland capable of secreting toxins (a derived trait). The phylogeny based on whole mitochondrial genomes, though, as proposed by Rest et al. (2003), places the green iguana as the closest relative of the
mole skink ''Plestiodon egregius'', the mole skink, is a species of small lizard endemic to the Southeastern United States. Taxonomy The species is subdivided into five subspecies, including the nominotypical subspecies: *Florida Keys mole skink, ''P. e ...
(''Plestiodon egregius'').
Lepidosaurs The Lepidosauria (, from Greek meaning ''scaled lizards'') is a subclass or superorder of reptiles, containing the orders Squamata and Rhynchocephalia. Squamata includes snakes, lizards, and amphisbaenians. Squamata contains over 9,000 species ...
are reptiles with overlapping scales, and within this group both iguanians and tuataras (''Sphenodon'') project their tongues to seize prey items instead of using their jaws, which is called tongue
prehension Prehensility is the quality of an appendage or organ that has adapted for grasping or holding. The word is derived from the Latin term ''prehendere'', meaning "to grasp". The ability to grasp is likely derived from a number of different origin ...
. Iguanians are the only lineage within the Squamata that display this trait, meaning that it was gained independently in both iguanians and tuataras. Iguanians are also the only squamates that primarily use their sight to identify and track prey rather than chemoreception or scent, and employ an ambush technique of catching prey instead of active searching. A study by Breuil ''et al.'' (2020) found the taxonomy of the genus ''Iguana'' as follows, with ''I. delicatissima'' being the most
basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...
member of the group. The species are classified as subspecies based on the ReptileDatabase definitions. The Reptile Database synonymizes ''I. rhinolopha'' with ''I. iguana'', only considering it a distinctive population, and recognizes ''I. insularis'' and ''I. melanoderma'' as
subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...
of ''I. iguana''. Four subspecies of green iguana are recognized under this treatment: ''I. i. insularis'' (
Saint Vincent & the Grenadines Saint Vincent and the Grenadines () is an island country in the Caribbean. It is located in the southeast Windward Islands of the Lesser Antilles, which lie in the West Indies at the southern end of the eastern border of the Caribbean Sea wh ...
and
Grenada Grenada ( ; Grenadian Creole French: ) is an island country in the West Indies in the Caribbean Sea at the southern end of the Grenadines island chain. Grenada consists of the island of Grenada itself, two smaller islands, Carriacou and Pe ...
), ''I. i. sanctaluciae'' (
Saint Lucia Saint Lucia ( acf, Sent Lisi, french: Sainte-Lucie) is an island country of the West Indies in the eastern Caribbean. The island was previously called Iouanalao and later Hewanorra, names given by the native Arawaks and Caribs, two Amerindian ...
), ''I. i. melanoderma'' (parts of the northern Lesser Antilles, and potentially coastal Venezuela, the Virgin Islands, and Puerto Rico), and ''I. i. iguana'' (mainland South America).


Extant species

Two extant species in the genus ''Iguana'' are widely recognized.


Subspecies

Three
Caribbean The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both the Caribbean Se ...
subspecies of the green iguana are also recognized: The Central American iguana (''I. rhinolopha'' or ''I. i. rhinolopha''), sometimes considered a distinct species, is largely considered synonymous with ''I. iguana'', as the presence of horns does not necessarily indicate a new species or subspecies. The two described subspecies of ''I. insularis'' (the Saint Lucia horned iguana, ''I. i. sanctaluciae'', and the Grenadines horned iguana, ''I. i. insularis'') were originally described as subspecies of ''I. iguana'', although they are genetically very similar and may not be separate subspecies from one another. Recent studies have recovered ''I. rhinolopha'' and ''I. insularis'' as distinct species based on genetics, but the Reptile Database disagrees with these conclusions, and classifies ''I. rhinolopha'' as synonymous with ''I. iguana'', and ''I. insularis'' as a subspecies of ''I. iguana''. The
Curaçao Curaçao ( ; ; pap, Kòrsou, ), officially the Country of Curaçao ( nl, Land Curaçao; pap, Pais Kòrsou), is a Lesser Antilles island country in the southern Caribbean Sea and the Dutch Caribbean region, about north of the Venezuela coast ...
population of green iguanas shows major genetic divergence and may also represent an as-of-yet undescribed species or subspecies.


As food

Iguanas have historically featured in the culinary traditions of Mexico and Central America. Iguana meat is also consumed in parts of the United States and Puerto Rico. Also, the eggs of iguana are consumed in some parts of Latin America, such as Nicaragua and Colombia.


References


Further reading

* *


External links

* {{Authority control Lizard genera Lizards of Central America Lizards of the Caribbean Lizards of North America Lizards of South America Taxa named by Josephus Nicolaus Laurenti cs:Leguánovití de:Leguan