Iguana

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Iguana
Portrait of an Iguana.jpg
A green iguana (Iguana iguana)
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Iguania
Family: Iguanidae
Genus: Iguana
Laurenti, 1768
Species
Synonyms
  • Hypsilophus Wagler, 1830

Iguana (/ɪˈɡwɑːnə/,[1][2] Spanish: [iˈɣwana]) is a genus of herbivorous lizards that are native to tropical areas of Mexico, Central America, South America, and the Caribbean. 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 included in the genus Iguana: 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 and endangered due to habitat destruction, introduced feral predators, hunting, and hybridization with introduced green iguanas.

The word "iguana" is derived from the original Taino name for the species, iwana.[3]

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".

Anatomy and physiology[edit]

Iguanas can range from 1.5 to 1.8 metres (5 to 6 ft) in length, including their tail. The two species of lizard within the genus Iguana possess a dewlap and a row of elongated scales running from the midline of their necks down to their tails. Iguanas have varying types of scales covering different areas of their body, for example, there are some large round tuberculate scales scattered around the lateral region of the neck among smaller, overlapping scales;[4] the scales on the dorsal trunk of their body are also thicker and more tightly packed than those on the ventral side.[4] 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 sub-tympanic shield.[5]

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.[5]

The tympanum, the iguana's eardrum, is located above the sub-tympanic 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.[5]

Like most reptiles, an iguana has a three-chambered heart with two atria, one ventricle, and two aortae with a systemic circulation.[6]

The dorsal view of the muscles of an adolescent iguana

The muscles of an iguana are very light in color, this is due to the high proportion of fast glycolytic muscle fibers; these fibers are not very vascularized and are low in myoglobin, giving them their pale look. This high density of fast glycolytic muscle 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 fast glycolytic muscle fibers is anaerobic.

The parietal eye of an adult iguana circled in red

Parietal eye[edit]

Several species of lizard, including the iguana, have a pale scale towards the back of their head marking the parietal eye; this organ is photosensitive to changes in illumination and sends signals to the pineal gland signaling the change between day and night. A photopigment commonly found in the lamprey, known as parapinopsin, is also found in the iguana and is photosensitive to UV light and aids in the signaling between day and night.[7]

Skull morphology and diet[edit]

Iguanas have an exclusively herbivorous diet,[8] as illustrated above by a green iguana eating a mango in Venezuela

Iguanas have developed a herbivorous lifestyle, foraging exclusively on vegetation and foliage.[8] In order 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 reptiles; the skull of the iguana has undergone modifications resulting in a strong bite force and efficient processing of vegetation, according to one study.[9]

In order to accomplish this biomechanically, herbivorous lizards (such as the iguana) have taller and wider skulls, shorter snouts, and larger bodies relative to carnivorous and omnivorous reptiles.[9] Increasing the robusticity of the skull allows for increased muscle presence and increases the ability of the skull to withstand stronger forces.[10]

Green Iguana skull (Iguana iguana).jpg: Brian Gratwicke derivative work: B kimmel (talk)
Green iguana skull and teeth. The teeth of the green iguana sit on the surface of the jawbone, known as acrodontal placement.[11]

Furthermore, the teeth of the iguana are acrodontal, meaning that their teeth sit on top of the surface of the jaw bone[11] and project upwards; the teeth themselves are small and serrated - designed to grasp and shear food.[12]

Reproduction[edit]

The early developed ovaries of an adolescent iguana are shaded in red

Male iguanas, like other male examples of Squamata, have two hemipenes. During copulation one hemipene will be inserted into the female's cloacal vent. Females 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.[citation needed]

Mating/courtship[edit]

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 amongst each other 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 will straddle the female and hold 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.[citation needed]

Phylogeny[edit]

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).[13] On the other hand, the phylogeny based on whole mitochondrial genomes, proposed by Rest et. al. (2003), places the green iguana as the closest relative of the mole skink (Plestiodon egregius). [14] Lepidosaurs are reptiles with overlapping scales, and within this group both iguanians and tuataras (Sphenodons) project their tongue to seize prey items instead of using their jaw, which is called tongue prehension. However, iguanians are the only lineage within Squamata that displays this trait, meaning that it was gained independently in both iguanians and tuataras. [13] 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.[13]

Simple phylogeny with Reptilia highlighted in green. Iguanians are within Lepidosauria.

Extant species[edit]

Image Scientific name Common Name Distribution
Iguana delicatissima in Coulibistrie e04.jpg Iguana delicatissima Lesser Antillean iguana the Lesser Antilles on Saint Barth, Anguilla, Sint Eustatius, Guadeloupe, Dominica, and Martinique
Iguana iguana Portoviejo 01.jpg Iguana iguana Green iguana southern Mexico to central Brazil, the Dominican Republic, Paraguay, Bolivia and the Caribbean; specifically Grenada, Aruba, Curaçao, Trinidad and Tobago, St. Lucia, St. Vincent, and Útila

Images[edit]

References[edit]

  1. ^ Cambridge Dictionary
  2. ^ Oxford Dictionaries
  3. ^ Coles, William (2002), "Green Iguana" (PDF), U.S.V.I. Animal Fact Sheet #08, Department of Planning and Natural Resources US Virgin Islands Division of Fish and Wildlife, archived from the original (PDF) on 2007-12-11
  4. ^ a b Chang, Cheng; Wu, Ping; Baker, Ruth E.; Maini, Philip K.; Alibardi, Lorenzo; Chuong, Cheng-Ming (2009). "Reptile scale paradigm: Evo-Devo, pattern formation and regeneration". The International Journal of Developmental Biology. 53 (5–6): 813–826. doi:10.1387/ijdb.072556cc. ISSN 0214-6282. PMC 2874329. PMID 19557687.
  5. ^ a b c Lazell, J.D. (1973), "The lizard genus Iguana in the Lesser Antilles", Bulletin of the Museum of Comparative Zoology, New York, 145, pp. 1–28
  6. ^ DABVP, Ryan S. De Voe DVM MSpVM DACZM. "Reptilian cardiovascular anatomy and physiology: evaluation and monitoring (Proceedings)". dvm360.com. Retrieved 2017-05-13.
  7. ^ Wada, Seiji (June 2012). "Expression of UV-Sensitive Parapinopsin in the Iguana Parietal Eyes and Its Implication in UV-Sensitivity in Vertebrate Pineal-Related Organs". PLOS ONE. 7 (6): 6. Bibcode:2012PLoSO...739003W. doi:10.1371/journal.pone.0039003. PMC 3375259. PMID 22720013.
  8. ^ a b Lichtenbelt, Wouter D. van Marken (1993-08-01). "Optimal foraging of a herbivorous lizard, the green iguana in a seasonal environment". Oecologia. 95 (2): 246–256. Bibcode:1993Oecol..95..246V. doi:10.1007/BF00323497. ISSN 0029-8549. PMID 28312949.
  9. ^ a b Metzger, Keith A.; Herrel, Anthony (2005-12-01). "Correlations between lizard cranial shape and diet: a quantitative, phylogenetically informed analysis". Biological Journal of the Linnean Society. 86 (4): 433–466. doi:10.1111/j.1095-8312.2005.00546.x. ISSN 0024-4066.
  10. ^ Herrel, Anthony (2009). "Jaw and hyolingual muscle activity patterns and bite forces in the herbivorous lizard Uromastyx acanthinurus". Archives of Oral Biology. 54 (8): 772–782. doi:10.1016/j.archoralbio.2009.05.002. PMID 19481732.
  11. ^ a b "THE TEETH OF VERTEBRATE ANIMALS". inside.ucumberlands.edu. University of the Cumberlands. April 28, 2017. Retrieved April 28, 2017.
  12. ^ Banzato, Tommaso; Selleri, Paolo; Veladiano, Irene A.; Martin, Andrea; Zanetti, Emanuele; Zotti, Alessandro (2012-01-01). "Comparative evaluation of the cadaveric, radiographic and computed tomographic anatomy of the heads of green iguana (Iguana iguana), common tegu ( Tupinambis merianae) and bearded dragon ( Pogona vitticeps)". BMC Veterinary Research. 8: 53. doi:10.1186/1746-6148-8-53. ISSN 1746-6148. PMC 3439268. PMID 22578088.
  13. ^ a b c Vidal, Nicolas; Hedges, S. Blair (2009). "The molecular evolutionary tree of lizards, snakes, and amphisbaenians". Comptes Rendus Biologies. 332 (2–3): 129–139. doi:10.1016/j.crvi.2008.07.010. PMID 19281946.
  14. ^ Rest, Joshua S.; Ast, Jennifer C.; Austin, Christopher C.; Waddell, Peter J.; Tibbetts, Elizabeth A.; Hay, Jennifer M.; Mindell, David P. (2003). "Molecular systematics of primary reptilian lineages and the tuatara mitochondrial genome". Molecular Phylogenetics and Evolution. 29 (2): 289–297. doi:10.1016/S1055-7903(03)00108-8.

Further reading[edit]

  • Frost, D. R. (1989). "A phylogenetic analysis and taxonomy of iguanian lizards". Pub Univ Kansas. 81: 1–65.
  • Frost, D. R.; Etheridge, R.; Janies, D.; Titus, T. A. (2001). "Total evidence, sequence alignment, evolution of polychrotid lizards, and a reclassification of the Iguania (Squamata: Iguania)". American Museum Novitates. 3343: 1–39. doi:10.1206/0003-0082(2001)343<0001:TESAEO>2.0.CO;2. hdl:2246/2896.