THE IGUANA

 

Iguana (/ɪˈɡwɑːnə/,^[3][4] 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 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.^[5][6]

The word "iguana" is derived from the original Taino name for the species, iwana.^[7] 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".^[8]

The species is a popular quarry for pets, and has been widely introduced beyond its native area, into Ishigaki Island, the Florida Peninsula, Hawaii, numerous islands in the Lesser Antilles, Singapore, Thailand, and Taiwan.^[9]

  A green iguana (Iguana iguana)

Anatomy and physiology

 

 

Iguanas are large lizards that can range from 1.2 to 2.0 m (4 to 6.5 ft) in length, including their tails. They 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, some large, round tuberculate scales are scattered around the lateral region of the neck among smaller, overlapping scales.^[10] The scales on the dorsal trunk of their bodies are also thicker and more tightly packed than those on the ventral sides.^[10] 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.^[11]

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.^[11]

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.^[11]

Like most reptiles, an iguana has a three-chambered heart with two atria, one ventricle, and two aortae with a systemic circulation.^[12] 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.

 

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 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.^[13]

 

 Skull morphology and diet

Iguanas have an exclusively herbivorous diet,^[14] as illustrated above by a green iguana eating a mango in Venezuela.

Iguanas have developed an herbivorous lifestyle, foraging exclusively on vegetation and foliage.^[14] 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.^[15] To accomplish this biomechanically, herbivorous lizards have taller and wider skulls, shorter snouts, and larger bodies relative to carnivorous and omnivorous reptiles.^[15] Increasing the strength of the skull allows for increased muscle presence and increases the ability of the skull to withstand stronger forces.^[16]

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

Furthermore, the teeth of the iguana are acrodontal, meaning that their teeth sit on top of the surface of the jaw bone^[17] and project upwards. The teeth themselves are small and serrated - designed to grasp and shear food.^[18]

 

Reproduction

 

Male iguanas, like other male examples of Squamata, have two hemipenes. During copulation, one hemipenis is inserted into the female's cloacal vent.^[19] 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.^[20][21][22]

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 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.^{[citation needed]}

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).^[23] 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).^[24] Lepidosaurs 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.^[23] 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.^[23]

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.^[5] The species are classified as subspecies based on the ReptileDatabase definitions.

	Sauromalus Iguana I. delicatissima I. iguana "I. i. rhinolopha" I. i. insularis I. i. sanctaluciae I. i. melanoderma I. i. iguana

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 and Grenada), 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.

Image	Scientific name	Common name	Distribution
	Iguana delicatissima	Lesser Antillean iguana	The Lesser Antilles on Saint Barth, Anguilla, Sint Eustatius, Guadeloupe, Dominica, and Martinique
	Iguana iguana	Green iguana	Most of South America, from Colombia east to French Guiana and south to northern Argentina. Also introduced to parts of the Caribbean. If other species formerly considered conspecific are included, ranges north to southern Mexico and the southern Caribbean; specifically Grenada, Aruba, Curaçao, Trinidad and Tobago, St. Lucia, St. Vincent, and Útila.

Subspecies

Three Caribbean subspecies of the green iguana are also recognized:

	I. i. insularis[25]	Grenadines horned iguana	St. Vincent and the Grenadines and Grenada
	Iguana iguana melanoderma[5]	Saban black iguana	Saba, Montserrat, and formerly Redonda, but also possibly coastal Venezuela, the Virgin Islands, and Puerto Rico (at least parts of this range may derive from (pre)historic introductions).
	I. i. sanctaluciae[25]	Saint Lucia horned iguana	St. Lucia

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.^[26] 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.^[27] The Curaçao population of green iguanas shows major genetic divergence and may also represent an as-of-yet undescribed species or subspecies.^[5][28]

 

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.^[29] Also, the eggs of iguana are consumed in some parts of Latin America, such as Nicaragua and Colombia.^[30]

 

 

 

 

 

 

 

THE CAPYBARA

 

 The capybara^{[note 1]} or greater capybara (Hydrochoerus hydrochaeris) is a giant cavy rodent native to South America. It is the largest living rodent^[2] and a member of the genus Hydrochoerus. The only other extant member is the lesser capybara (Hydrochoerus isthmius). Its close relatives include guinea pigs and rock cavies, and it is more distantly related to the agouti, the chinchilla, and the nutria. The capybara inhabits savannas and dense forests, and lives near bodies of water. It is a highly social species and can be found in groups as large as 100 individuals, but usually live in groups of 10–20 individuals. The capybara is hunted for its meat and hide and also for grease from its thick fatty skin.^[3] It is not considered a threatened species.

 At Pantanal, Brazil

Etymology

 

 Its common name is derived from Tupi ka'apiûara, a complex agglutination of kaá (leaf) + píi (slender) + ú (eat) + ara (a suffix for agent nouns), meaning "one who eats slender leaves", or "grass-eater".^[4]

The scientific name, both hydrochoerus and hydrochaeris, comes from Greek ὕδωρ (hydor "water") and χοῖρος (choiros "pig, hog").^[5][6]

 

Classification and phylogeny

 

The capybara and the lesser capybara both belong to the subfamily Hydrochoerinae along with the rock cavies. The living capybaras and their extinct relatives were previously classified in their own family Hydrochoeridae.^[7] Since 2002, molecular phylogenetic studies have recognized a close relationship between Hydrochoerus and Kerodon, the rock cavies,^[8] supporting placement of both genera in a subfamily of Caviidae.^[5]

Paleontological classifications previously used Hydrochoeridae for all capybaras, while using Hydrochoerinae for the living genus and its closest fossil relatives, such as Neochoerus,^[9][10] but more recently have adopted the classification of Hydrochoerinae within Caviidae.^[11] The taxonomy of fossil hydrochoerines is also in a state of flux. In recent years, the diversity of fossil hydrochoerines has been substantially reduced.^[9][10] This is largely due to the recognition that capybara molar teeth show strong variation in shape over the life of an individual.^[9] In one instance, material once referred to four genera and seven species on the basis of differences in molar shape is now thought to represent differently aged individuals of a single species, Cardiatherium paranense.^[9] Among fossil species, the name "capybara" can refer to the many species of Hydrochoerinae that are more closely related to the modern Hydrochoerus than to the "cardiomyine" rodents like Cardiomys.^[11] The fossil genera Cardiatherium, Phugatherium, Hydrochoeropsis, and Neochoerus are all capybaras under that concept.^[11]

 

 Description

Taxidermy specimen of a capybara

The capybara has a heavy, barrel-shaped body and short head, with reddish-brown fur on the upper part of its body that turns yellowish-brown underneath. Its sweat glands can be found in the surface of the hairy portions of its skin, an unusual trait among rodents.^[7] The animal lacks down hair, and its guard hair differs little from over hair.^[12]

Adult capybaras grow to 106 to 134 cm (3.48 to 4.40 ft) in length, stand 50 to 62 cm (20 to 24 in) tall at the withers, and typically weigh 35 to 66 kg (77 to 146 lb), with an average in the Venezuelan llanos of 48.9 kg (108 lb).^[13][14][15] Females are slightly heavier than males. The top recorded weights are 91 kg (201 lb) for a wild female from Brazil and 73.5 kg (162 lb) for a wild male from Uruguay.^[7][16] Also, an 81 kg individual was reported in São Paulo in 2001 or 2002.^[17] The dental formula is 1.0.1.31.0.1.3.^[7] Capybaras have slightly webbed feet and vestigial tails.^[7] Their hind legs are slightly longer than their forelegs; they have three toes on their rear feet and four toes on their front feet.^[18] Their muzzles are blunt, with nostrils, and the eyes and ears are near the top of their heads.

Its karyotype has 2n = 66 and FN = 102, meaning it has 66 chromosomes with a total of 102 arms.^[5][7]

 

Ecology

Yellow-headed caracara on a capybara

A family of capybara swimming

Capybaras are semiaquatic mammals^[15] found throughout all countries of South America except Chile.^[19] They live in densely forested areas near bodies of water, such as lakes, rivers, swamps, ponds, and marshes,^[14] as well as flooded savannah and along rivers in the tropical rainforest. They are superb swimmers and can hold their breath underwater for up to five minutes at a time. Capybara have flourished in cattle ranches.^[7] They roam in home ranges averaging 10 hectares (25 acres) in high-density populations.^[7]

Many escapees from captivity can also be found in similar watery habitats around the world. Sightings are fairly common in Florida, although a breeding population has not yet been confirmed.^[20] In 2011, one specimen was spotted on the Central Coast of California.^[21] These escaped populations occur in areas where prehistoric capybaras inhabited; late Pleistocene capybaras inhabited Florida^[22] and Hydrochoerus hesperotiganites in California and Hydrochoerus gaylordi in Grenada, and feral capybaras in North America may actually fill the ecological niche of the Pleistocene species.^[23]

 

Diet and predation

A capybara eating hay at Franklin Park Zoo, Boston, Massachusetts

Capybaras are herbivores, grazing mainly on grasses and aquatic plants,^[14][24] as well as fruit and tree bark.^[15] They are very selective feeders^[25] and feed on the leaves of one species and disregard other species surrounding it. They eat a greater variety of plants during the dry season, as fewer plants are available. While they eat grass during the wet season, they have to switch to more abundant reeds during the dry season.^[26] Plants that capybaras eat during the summer lose their nutritional value in the winter, so they are not consumed at that time.^[25] The capybara's jaw hinge is not perpendicular, so they chew food by grinding back-and-forth rather than side-to-side.^[27] Capybaras are autocoprophagous,^[28] meaning they eat their own feces as a source of bacterial gut flora, to help digest the cellulose in the grass that forms their normal diet, and to extract the maximum protein and vitamins from their food. They also regurgitate food to masticate again, similar to cud-chewing by cattle.^[28][29] As is the case with other rodents, the front teeth of capybaras grow continually to compensate for the constant wear from eating grasses;^[19] their cheek teeth also grow continuously.^[27]

Cattle tyrant on a capybara

Like its relative the guinea pig, the capybara does not have the capacity to synthesize vitamin C, and capybaras not supplemented with vitamin C in captivity have been reported to develop gum disease as a sign of scurvy.^[30]

They can have a lifespan of 8–10 years,^[31] but tend to live less than four years in the wild due to predation from jaguars, pumas, ocelots, eagles, and caimans.^[19] The capybara is also the preferred prey of the green anaconda.^[32]

 

Social organization

Capybaras have a scent gland on their noses.

Capybaras are known to be gregarious. While they sometimes live solitarily, they are more commonly found in groups of around 10–20 individuals, with two to four adult males, four to seven adult females, and the remainder juveniles.^[33] Capybara groups can consist of as many as 50 or 100 individuals during the dry season^[29][34] when the animals gather around available water sources. Males establish social bonds, dominance, or general group consensus.^[34] They can make dog-like barks^[29] when threatened or when females are herding young.^[35]

Capybaras have two types of scent glands: a morrillo, located on the snout, and anal glands.^[36] Both sexes have these glands, but males have much larger morrillos and use their anal glands more frequently. The anal glands of males are also lined with detachable hairs. A crystalline form of scent secretion is coated on these hairs and is released when in contact with objects such as plants. These hairs have a longer-lasting scent mark and are tasted by other capybaras. Capybaras scent-mark by rubbing their morrillos on objects, or by walking over scrub and marking it with their anal glands. Capybaras can spread their scent further by urinating; however, females usually mark without urinating and scent-mark less frequently than males overall. Females mark more often during the wet season when they are in estrus. In addition to objects, males also scent-mark females.^[36]

 

 

Reproduction

Mother with typical litter of about four pups

Capybara mother with her pups

When in estrus, the female's scent changes subtly and nearby males begin pursuit.^[37] In addition, a female alerts males she is in estrus by whistling through her nose.^[29] During mating, the female has the advantage and mating choice. Capybaras mate only in water, and if a female does not want to mate with a certain male, she either submerges or leaves the water.^[29][34] Dominant males are highly protective of the females, but they usually cannot prevent some of the subordinates from copulating.^[37] The larger the group, the harder it is for the male to watch all the females. Dominant males secure significantly more matings than each subordinate, but subordinate males, as a class, are responsible for more matings than each dominant male.^[37] The lifespan of the capybara's sperm is longer than that of other rodents.^[38]

Mother and three pups

Capybara gestation is 130–150 days, and produces a litter of four young on average, but may produce between one and eight in a single litter.^[7] Birth is on land and the female rejoins the group within a few hours of delivering the newborn capybaras, which join the group as soon as they are mobile. Within a week, the young can eat grass, but continue to suckle—from any female in the group—until weaned around 16 weeks. The young form a group within the main group.^[19] Alloparenting has been observed in this species.^[34] Breeding peaks between April and May in Venezuela and between October and November in Mato Grosso, Brazil.^[7]

 

Activities

 

Though quite agile on land, capybaras are equally at home in the water. They are excellent swimmers, and can remain completely submerged for up to five minutes,^[14] an ability they use to evade predators. Capybaras can sleep in water, keeping only their noses out. As temperatures increase during the day, they wallow in water and then graze during the late afternoon and early evening.^[7] They also spend time wallowing in mud.^[18] They rest around midnight and then continue to graze before dawn.^[7]

 

Conservation and human interaction

Capybaras are not considered a threatened species;^[1] their population is stable throughout most of their South American range, though in some areas hunting has reduced their numbers.^[14][19]

Capybaras are hunted for their meat and pelts in some areas,^[39] and otherwise killed by humans who see their grazing as competition for livestock. In some areas, they are farmed, which has the effect of ensuring the wetland habitats are protected. Their survival is aided by their ability to breed rapidly.^[19]

Capybaras have adapted well to urbanization in South America. They can be found in many areas in zoos and parks,^[27] and may live for 12 years in captivity, more than double their wild lifespan.^[19] Capybaras are docile and usually allow humans to pet and hand-feed them, but physical contact is normally discouraged, as their ticks can be vectors to Rocky Mountain spotted fever.^[40]

The European Association of Zoos and Aquaria asked Drusillas Park in Alfriston, Sussex, England, to keep the studbook for capybaras, to monitor captive populations in Europe. The studbook includes information about all births, deaths and movements of capybaras, as well as how they are related.^[41]

Capybaras are farmed for meat and skins in South America.^[42] The meat is considered unsuitable to eat in some areas, while in other areas it is considered an important source of protein.^[7] In parts of South America, especially in Venezuela, capybara meat is popular during Lent and Holy Week as the Catholic Church previously issued special dispensation to allow it to be eaten while other meats are generally forbidden.^[43] After several attempts a 1784 Papal bull was obtained that allowed the consumption of capybara during Lent.^[44][45] There is widespread perception in Venezuela that consumption of capybaras is exclusive to rural people.^[46]

Although it is illegal in some states,^[47] capybaras are occasionally kept as pets in the United States.^[48]

The image of a capybara features on the 2-peso coin of Uruguay.^[49]

In Japan, following the lead of Izu Shaboten Zoo in 1982,^[50] multiple establishments or zoos in Japan that raise capybaras have adopted the practice of having them relax in onsen during the winter. They are seen as an attraction by Japanese people.^[50] Capybaras became big in Japan due to the popular cartoon character Kapibara-san.^[51]

In August 2021, Argentine and international media reported that capybaras had been causing serious problems for residents of Nordelta, an affluent gated community north of Buenos Aires built atop wetland habitat. This inspired Argentine and worldwide leftists to jokingly adopt the capybara as a symbol of class struggle and communism.^[52][53]

Brazilian Lyme-like borreliosis likely involves capybaras as reservoirs and Amblyomma and Rhipicephalus ticks as vectors.^[54]

 

 

Popularity and meme culture

 

 

In the early 2020s, capybaras became a growing figure of meme culture due to many factors, including the disturbances in Nordelta^[53] which led to them being comically postulated as figures of class struggle. Also, a common meme format includes capybaras in various situations with the song "After Party" by Don Toliver,^[55] leading to a tremendous growth in popularity.^[56] Due to a lyric in Toliver's song, capybaras are also associated with the phrase "Ok I pull up".^[57]

•  

  Binomial name

  Hydrochoerus hydrochaeris
  

  (Linnaeus, 1766)
  
  
  
  
  
  Native range