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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 nomencla ...
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 ...
lizard Lizards are a widespread group of Squamata, 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 Amphisbae ...
s 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. C ...
, 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 S ...
. 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 ' (176 ...
in his book ''Specimen Medicum, Exhibens Synopsin Reptilium Emendatam cum Experimentis circa Venena''. Two
species In biology, a species is the basic unit of Taxonomy (biology), 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 ...
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 feral p ...
, which is native to the Lesser Antilles. 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, 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 Squamata, 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 Amphisbae ...
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 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 co ...
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 ...
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, 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. 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 patterns in both circadian and seasonal cycl ...
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 ...
, 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 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 so ...
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, 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, 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. 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 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 in ...
s 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 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 individ ...
reproduction.


Phylogeny

A phylogeny 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 sys ...
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'').
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 specie ...
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. 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 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 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 ...
), ''I. i. sanctaluciae'' ( Saint Lucia), ''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 S ...
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