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''Iguana'' (, ) is a
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of
herbivorous A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...
lizards that are native to tropical areas of
Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...
,
Central America Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...
,
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...
, and the Caribbean. The genus was first described in 1768 by Austrian naturalist
Josephus Nicolaus Laurenti Josephus Nicolaus Laurenti (4 December 1735, Vienna – 17 February 1805, Vienna) was an Austrian naturalist and zoologist of Italian origin. Laurenti is considered the auctor of the class Reptilia ( reptiles) through his authorship of ' (1 ...
in his book ''Specimen Medicum, Exhibens Synopsin Reptilium Emendatam cum Experimentis circa Venena''. Two
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
are placed in the genus, the green iguana, which is widespread throughout its range and a popular pet, and the
Lesser Antillean iguana The Lesser Antillean iguana (''Iguana delicatissima'') is a large arboreal lizard endemic to the Lesser Antilles. It is one of three species of lizard of the genus '' Iguana'' and is in severe decline due to habitat destruction, introduced fera ...
, which is native to the
Lesser Antilles The Lesser Antilles ( es, link=no, Antillas Menores; french: link=no, Petites Antilles; pap, Antias Menor; nl, Kleine Antillen) are a group of islands in the Caribbean Sea. Most of them are part of a long, partially volcanic island arc bet ...
. Genetic analysis indicates that the green iguana may comprise a
complex Complex commonly refers to: * Complexity, the behaviour of a system whose components interact in multiple ways so possible interactions are difficult to describe ** Complex system, a system composed of many components which may interact with each ...
of multiple species, some of which have been recently described, but the
Reptile Database The Reptile Database is a scientific database that collects taxonomic information on all living reptile species (i.e. no fossil species such as dinosaurs). The database focuses on species (as opposed to higher ranks such as families) and has entrie ...
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
pet A pet, or companion animal, is an animal kept primarily for a person's company or entertainment rather than as a working animal, livestock, or a laboratory animal. Popular pets are often considered to have attractive appearances, intelligence ...
s, and has been widely introduced beyond its native area, into
Ishigaki Island , also known as ''Ishigakijima'', is a Japanese island south-west of Okinawa Hontō and the second-largest island of the Yaeyama Island group, behind Iriomote Island. It is located approximately south-west of Okinawa Hontō. It is within the ...
,
Florida Peninsula A peninsula ( la, paeninsula from ''paene'' "almost" and ''insula'' "island") is a piece of land that is bordered mostly by water but connected to mainland. The surrounding water is usually understood to be continuous, though not necessarily nam ...
,
Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only state ...
, numerous islands in the
Lesser Antilles The Lesser Antilles ( es, link=no, Antillas Menores; french: link=no, Petites Antilles; pap, Antias Menor; nl, Kleine Antillen) are a group of islands in the Caribbean Sea. Most of them are part of a long, partially volcanic island arc bet ...
,
Singapore Singapore (), officially the Republic of Singapore, is a sovereign island country and city-state in maritime Southeast Asia. It lies about one degree of latitude () north of the equator, off the southern tip of the Malay Peninsula, bor ...
,
Thailand Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is b ...
, and
Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...
.


Anatomy and physiology

Iguanas can range from in length, including their tails. These lizards possess a
dewlap A dewlap is a longitudinal flap of skin or similar flesh that hangs beneath the lower jaw or neck of many vertebrates. More loosely, it can be various similar structures in the neck area, such as those caused by a double chin or the submandibul ...
and a row of elongated scales running from the midline of their necks down to their
tail The tail is the section at the rear end of certain kinds of animals’ bodies; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammal ...
s. 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 Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal c ...
trunk of their bodies are also thicker and more tightly packed than those on the
ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
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, 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 reptiles, an iguana has a three-chambered
heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to t ...
with two atria, one ventricle, and two aortae with a systemic circulation. 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, 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 Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: * Anaerobic adhesive, a bonding a ...
.


Parietal eye

Several species of lizards, including the iguanas, have a pale scale towards the back of their heads marking the
parietal eye A parietal eye, also known as a third eye or pineal eye, is a part of the epithalamus present in some vertebrates. The eye is located at the top of the head, is photoreceptive and is associated with the pineal gland, regulating circadian rhyth ...
. This organ is sensitive to changes in illumination and sends signals to the pineal gland noting the change between day and night. A photopigment commonly found in the
lamprey Lampreys (sometimes inaccurately called lamprey eels) are an ancient extant lineage of jawless fish of the order Petromyzontiformes , placed in the superclass Cyclostomata. The adult lamprey may be characterized by a toothed, funnel-like s ...
, 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 A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...
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 or
omnivorous An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nut ...
reptiles. The skull of the iguana has undergone modifications resulting in a strong bite force and efficient processing of
vegetation Vegetation is an assemblage of plant species and the ground cover they provide. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characte ...
, according to one study. To accomplish this biomechanically, 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
acrodont Acrodonty (from Greek ''akros'' 'highest' + ''dont'' 'tooth') is an anatomical placement of the teeth at the summit of the alveolar ridge of the jaw, without sockets, characteristic of bony fish. Functionally, acrodont tooth implantation may be rela ...
al, 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 Squamata (, Latin ''squamatus'', 'scaly, having scales') is the largest order of reptiles, comprising lizards, snakes, and amphisbaenians (worm lizards), which are collectively known as squamates or scaled reptiles. With over 10,900 species ...
, have two
hemipenes A hemipenis (plural hemipenes) is one of a pair of intromittent organs of male squamates (snakes, lizards and worm lizards). Hemipenes are usually held inverted within the body, and are everted for reproduction via erectile tissue, much like ...
. During copulation, one hemipenis is inserted into the female's
cloacal vent In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, ...
. 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 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 A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...
secreted from the
femoral pore Femoral pores are a part of a holocrine secretory gland found on the inside of the thighs of certain lizards and amphisbaenians which releases pheromones to attract mates or mark territory. In certain species only the male has these pores and i ...
s on the dorsal side of their hind limbs. Male behavior during sexual competition involves head bobbing, extending and retracting their
dewlap A dewlap is a longitudinal flap of skin or similar flesh that hangs beneath the lower jaw or neck of many vertebrates. More loosely, it can be various similar structures in the neck area, such as those caused by a double chin or the submandibul ...
, 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 In ecology, ''r''/''K'' selection theory relates to the selection of combinations of traits in an organism that trade off between quantity and quality of offspring. The focus on either an increased quantity of offspring at the expense of indivi ...
reproduction.


Phylogeny

A
phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spe ...
based on nuclear protein-coding genes, reviewed by Vidal and Hedges (2009), suggested that the
subclade In genetics, a subclade is a subgroup of a haplogroup. Naming convention Although human mitochondrial DNA (mtDNA) and Y chromosome DNA (Y-DNA) haplogroups and subclades are named in a similar manner, their names belong to completely separate sy ...
Iguania Iguania is an infraorder of squamate reptiles that includes iguanas, chameleons, agamids, and New World lizards like anoles and phrynosomatids. Using morphological features as a guide to evolutionary relationships, the Iguania are believed ...
is in a group with
snake Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more j ...
s 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 Endemism, endemic to the Southeastern United States. Taxonomy The species is subdivided into five subspecies, including the nominotypical subspecies: *Florida Keys mole ski ...
(''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
tuatara Tuatara (''Sphenodon punctatus'') are reptiles endemic to New Zealand. Despite their close resemblance to lizards, they are part of a distinct lineage, the order Rhynchocephalia. The name ''tuatara'' is derived from the Māori language and m ...
s (''Sphenodon'') project their tongues to seize prey items instead of using their jaws, which is called tongue prehension. Iguanians are the only lineage within the
Squamata Squamata (, Latin ''squamatus'', 'scaly, having scales') is the largest order of reptiles, comprising lizards, snakes, and amphisbaenians (worm lizards), which are collectively known as squamates or scaled reptiles. With over 10,900 species ...
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 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 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), ''I. i. sanctaluciae'' ( Saint Lucia), ''I. i. melanoderma'' (parts of the northern Lesser Antilles, and potentially coastal
Venezuela Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in th ...
, the
Virgin Islands The Virgin Islands ( es, Islas Vírgenes) are an archipelago in the Caribbean Sea. They are geologically and biogeographically the easternmost part of the Greater Antilles, the northern islands belonging to the Puerto Rico Trench and St. Cro ...
, and
Puerto Rico Puerto Rico (; abbreviated PR; tnq, Boriken, ''Borinquen''), officially the Commonwealth of Puerto Rico ( es, link=yes, Estado Libre Asociado de Puerto Rico, lit=Free Associated State of Puerto Rico), is a Caribbean island and unincorporated ...
), and ''I. i. iguana'' (mainland South America).


Extant species

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


Subspecies

Three Caribbean 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 population of green iguanas shows major genetic divergence and may also represent an as-of-yet
undescribed species In taxonomy, an undescribed taxon is a taxon (for example, a species) that has been discovered, but not yet formally described and named. The various Nomenclature Codes specify the requirements for a new taxon to be validly described and named. U ...
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