Blue Iguana
Encyclopedia
The Blue Iguana or Grand Cayman Iguana (Cyclura lewisi) is a critically endangered species of lizard
of the genus Cyclura
endemic to the island of Grand Cayman
. Previously listed as a subspecies of the Cuban Iguana
, it was reclassified as a separate species in 2004 because of genetic differences discovered four years earlier. The Blue Iguana is one of the longest-living species of lizard (possibly up to 69 years). The record is 67 years.
The Blue Iguana prefers dwelling in rocky, sunlit, open areas in dry forests or near the shore, as the females must dig holes in the sand to lay eggs in June and July. A possible second clutch is laid in September. The Blue Iguana's vegetarian diet includes plants, fruits, and flowers. Its coloration is tan to gray with a bluish cast that is more pronounced during the breeding season and more so in males. It is large and heavy-bodied with a dorsal crest of short spines running from the base of the neck to the end of the tail.
The fossil record indicates that the Blue Iguana was abundant before European colonization; but fewer than 15 animals remained in the wild by 2003, and this wild population was predicted to become extinct within the first decade of the 21st century. The species' decline is mainly being driven by predation
by feral pets (cats and dogs) and indirectly by the destruction of their natural habitat
as fruit farms are converted to pasture for cattle grazing. Since 2004, 219 captive-bred animals have been released into a preserve on Grand Cayman run by a partnership headed by the Durrell Wildlife Conservation Trust
, in an attempt to save the species. At least five non-profit organizations are working with the government of the Cayman Islands to ensure the survival of the Blue Iguana.
name (Cyclura
) is derived from the Ancient Greek
words cyclos (κύκλος) meaning "circular" and ourá (οὐρά) meaning "tail", after the thick-ringed tail characteristic of all Cyclura. Its specific
name is a Latinized
form of the name of the scientist who first described this species, Bernard C. Lewis. Its closest relatives are the Cuban Iguana (Cyclura nubila) and the Northern Bahamian Rock Iguana
(Cyclura cychlura), the three species having diverged from a common ancestor some three million years ago. The species has a low genetic diversity
but does not seem to suffer the same lack of vitality that afflicts other such species of rock iguana. One theory is that the species evolved from a single female Cuban Iguana (C. nubila nubila) with eggs inside her who drifted
across the sea, perhaps during a storm. It is distinct from the subspecies found on Little Cayman
and Cayman Brac
known as C. nubila caymanensis
, although it can breed with this subspecies and produce fertile offspring.
In 1938, Bernard C. Lewis of the Institute of Jamaica joined an Oxford University biological expedition to the Cayman Islands. Lewis was able to obtain two Blue Iguanas, a male and a female, which were later lodged with the British Museum
of Natural History. Chapman Grant
, in a monograph published in 1940, formally described the Blue Iguana for the first time as Cyclura macleayi lewisi. Schwartz and Carey established the trinomial
(Cyclura nubila lewisi) in 1977. They held that the Blue Iguana was a strongly distinct subspecies of the Cuban Iguana (C. nubila), the species which it evolved from and can breed with. They emphasized its overall bright blue coloration, and noted that further study could reveal it to be a distinct species. Frederick Burton reclassified the Blue Iguana as a distinct species in 2004, after years of research comparing scale counts on the heads of Caribbean iguanas, including those found on Little Cayman, Cayman Brac, Cuba, and the Bahamas, as well as mitochondrial DNA
analysis performed by Dr. Catherine Malone, to re-examine the phylogeography
of the different species.
chevrons from the crest of their necks to their pelvic area. These markings fade by the time the animal is one year old, changing to mottled gray and cream and eventually giving way to blue as adults. The adult Blue Iguana is typically dark gray matching the karst
rock of its landscape. The animal changes its color to blue when it is in the presence of other iguanas to signal and establish territory. The blue color is more pronounced in males of the species. Their distinctive black feet stand in contrast to their lighter overall body color. Male Blue Iguanas have prominent femoral pore
s, which are used to release pheromone
s. Females have smaller pores and have a less prominent dorsal crest, making the animal somewhat sexually dimorphic
.
and red sclera
. They have excellent vision, which allows them to detect shapes and motions at long distances. As Blue Iguanas have only a few rod cell
s, they have poor vision in low-light conditions. At the same time, they have cells
called "double cone
s" which give them sharp color vision and enable them to see ultraviolet
wavelengths. This ability is highly useful when basking so the animal can ensure that it absorbs enough sunlight in the forms of UVA and UVB to produce Vitamin D
.
Blue Iguanas have evolved a white photosensory organ on the top of their heads called the parietal eye
(also known as the third eye, pineal eye or pineal gland). This "eye" does not work the same way as a normal eye as it has only a rudimentary retina and lens and thus, cannot form images. It is however sensitive to changes in light and dark and can detect movement.
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The Blue Iguana is found only on the island of Grand Cayman
. Comparison with other Cyclura species in the region strongly suggests that there was once a coastal population of Blue Iguanas which was gradually displaced or extirpated by human settlements and the construction of roads. The Blue Iguana now only occurs inland in natural xerophytic shrubland and along the interfaces between farm clearings, roads, and gardens and closed-canopy dry forest or shrubland. The interior population is believed to have been attracted to agricultural clearings and fruit farms which provide thermoregulatory opportunities, herbaceous browse, fallen fruit, and nesting soil, but this also brought the Blue Iguana into contact with humans and feral animals. Females often migrate to coastal areas to nest.
Blue Iguanas released into the Queen Elizabeth II Botanic Park
on Grand Cayman were radiotracked in 2004 to determine ranges for each animal. Females were found to occupy territories of 0.6 acre (2,428.1 m²) and males an average of 1.4 acre (5,665.6 m²) with overlap in common territories, indicating that they choose to maintain a population density
of four to five animals per hectare
.
The Blue Iguanas occupy rock holes and tree cavities, and as adults are primarily terrestrial. Younger individuals tend to be more arboreal. Hatchlings are preyed upon by the native snake Alsophis cantherigerus
. The adults have no natural predators but can fall victim to feral dogs. They typically reach sexual maturity at three to four years of age.
: plant matter contains more potassium
and as it has less nutritional content per gram, more must be eaten to meet the lizard's metabolic needs. As they are not capable of creating urine more concentrated than their bodily fluids, they excrete nitrogenous wastes as uric acid salts through a salt gland
in the same manner as bird
s. As a result, they have developed this lateral nasal gland to supplement renal salt secretion by expelling excess potassium and sodium chloride.
Longevity in the wild is unknown but is presumed to be many decades. A Blue Iguana named "Godzilla" captured on Grand Cayman in 1950 by naturalist Ira Thompson was imported to the United States in 1985 by Ramon Noegel and sold to reptile importer and breeder, Tom Crutchfield in 1990. Crutchfield donated Godzilla to the Gladys Porter Zoo
in Brownsville
, Texas
in 1997 and the lizard remained there until its death in 2004. Thompson estimated Godzilla to be 15 years of age at the time of his capture. At an estimated 69 years of age (54 of which were spent in captivity), Godzilla may be the world's longest-living lizard for which there is reliable record. A closely related Lesser Caymans Iguana (C. nubila caymanensis
) has been documented as living 33 years in captivity.
Individuals are aggressively territorial from the age of about three months onward. Females occupy overlapping areas of the order of 0.6 acre (2,428.1 m²) seemingly regardless of age, while males occupy progressively larger and more extensively overlapping territories as they age and grow.
The Blue Iguana is listed as critically endangered on the IUCN Red List
. The population is restricted to the eastern interior of Grand Cayman, where it had been reduced to a critically low level, only three animals having been observed before the survey in 1988. The range of the Blue Iguana has contracted significantly over the past 25 years, with many sites once populated now showing no signs of iguanas. Surveys in 2003 indicated a total population in the range of 5–15 individuals. By 2005 the unmanaged wild population was considered to be functionally extinct. The species is one of the most endangered animals on Earth. A further blow to the dwindling population came in May 2008 when six individuals were found butchered in a nature preserve.
As the Blue Iguana consumes a variety of plant material, favoring fruits and flowers over leaves and stems when available, it is valuable on Grand Cayman as a seed disperser throughout its range. A study in 2000 by Dr Allison Alberts revealed that seeds passing through the digestive tracts of Cycluras germinate more rapidly than those that do not. These seeds in the fruits consumed by the Blue Iguana have an adaptive advantage by sprouting before the end of very short rainy seasons. The Blue Iguana is also an important means of distributing seeds to new areas and, as the largest native herbivore of Grand Cayman's ecosystems, it is essential for maintaining the delicate balance between climate and vegetation necessary to survive under harsh conditions.
Restored free-roaming subpopulations in the Queen Elizabeth II Botanic Park and the Salina Reserve numbered approximately 125 individuals in total after a release in December 2005. The restored subpopulation in the Queen Elizabeth II Botanic Park has been breeding since 2001, and the subpopulation in the Salina Reserve was deemed to be breeding in 2006 after a nest of three hatched eggs was discovered in the wild. As of April 2007, after another large-scale release, there are 299 Blue Iguanas living in the wild, with hundreds more being raised in captivity on Grand Cayman.
Predation and injury to hatchlings by rat
s, to hatchlings and sub-adults by feral cat
s, and killing of adults by roaming dogs
are all placing severe pressure on the remaining wild population. Automobiles and motorscooters are an increasing cause of mortality as the iguanas rarely survive the collisions. Trapping and shooting is a comparatively minor concern, but occasional trapping continues despite legal protection and sustained efforts to increase public awareness.
The common Green Iguana
, (Iguana iguana), has been introduced from Honduras
and is well-established on Grand Cayman as an invasive species
. It far outnumbers the endemic Blue Iguana. No direct negative consequences of this introduction on the Blue Iguana are known, but the mere presence of the Green Iguana confuses public attitudes and understanding. For example, the people of the island are told that Blue Iguanas are endangered and rare, and when they subsequently see large numbers of the introduced Green Iguana, they do not understand the difference.
Blue Iguanas used to regularly be sold to tourists as pets, as their rarity made them appealing to exotic-animal collectors, despite this being illegal under the CITES treaty. In 1999 a World Wildlife Fund international conservation officer, Stuart Chapman, said, "The British government has turned a blind eye for over 20 years to these overseas territories which are home to many rare and endangered species. Many of these face extinction if Britain fails to honour its treaty obligations. The British Caribbean islands are extremely rich in biodiversity with many critically endangered species
that are unique to the islands—yet there is virtually zero enforcement or implementation of CITES."
In May 2008, six Blue Iguanas were found dead in the preserve within Queen Elizabeth II Botanic Park on Grand Cayman. The iguanas were apparently killed by human vandals armed with knives and two of the slaughtered animals were gravid females about to lay eggs.
The wild population of Blue Iguanas had been reduced from a near island-wide distribution to a non-viable, fragmented remnant. By 2001, no young hatched in the unmanaged wild population were surviving to breeding age, meaning the population was functionally extinct, with only five animals remaining in the wild.
captive breeding program for the Blue Iguana, which at the time was the most critically endangered of all the species of Cyclura.
One of the early difficulties encountered was that the captive stock of the early 1990s was found not to be pure. It was discovered through DNA analysis that the captive population contained a number of animals that were hybrids with C. nubila caymanensis. The program contains only pure specimens, as these hybrids were sterilized by means of hemipenectomies and hence excluded. This program was created to determine the exact genealogies of the limited gene pool of the remaining animals and DNA analysis revealed that the entire North American captive population was descended from a single pair of animals. After five years of research two captive breeding populations were established and are managed as a single unit, with cross-breeding between the populations to promote genetic diversity.
As a hedge against disaster striking the Blue Iguana population on Grand Cayman, an off-island captive population was established in 25 zoos in the USA. A minimum of 20 founder lines represented by at least 225 individuals is being maintained by captive breeding and recorded in a studbook for the species by Tandora Grant of the San Diego Zoo
's Center for Conservation and Research for Endangered Species (CRES). The Indianapolis Zoo
has had success with breeding the Blue Iguana in captivity twice since the year 2000.
In October 2006, hatchlings were released into the wild for the first time to boost the species and help bring them back from the brink of extinction. Each released Blue Iguana wears a string of colored beads through its nuchal
crest for visual identification at a distance, backed up by an implanted microchip
and a high-resolution photograph of its head scales. (Head scale patterns are as unique among Blue Iguanas as fingerprints are among humans.)
The Blue Iguana is established in captivity, both in public and private collections. As there are very few pure-bred animals in private collections, private individuals have established these animals in captive breeding programs as hybrids with the Lesser Caymans Iguana (C.nubila caymanensis) and occasional hybrids with the Cuban Iguana (C.n.nubila) minimizing the demand for wild-caught specimens for the pet trade.
, International Reptile Conservation Foundation, IRCF, and the European Commission
. This program operates under a special exemption from provisions in the Animals Law of the Cayman Islands which normally would make it illegal for anyone to kill, capture, or keep iguanas. BIRP's conservation
strategy involves generating large numbers of genetically diverse hatchlings, head-starting them for two years where their chance of survival in the wild is high, and using these animals to rebuild a series of wild sub-populations in protected, managed natural areas. This is accompanied by field research, nest site protection, and monitoring of the released animals. A rapid numerical increase from a maximum possible number of founding stock is sought to minimize loss of genetic diversity caused by the "population bottleneck
".
Restored sub-populations are already present in two non-contiguous areas—the Salina Reserve and the Queen Elizabeth II Botanic Park. Habitat protection is still vital, as the Salina Reserve has only 88 acre (356,123.7 m²) of dry shrubland, which is not enough to sustain the 1,000 Blue Iguanas that must be restored to the wild to remove this species from the Critically Endangered List. Additional separate sub-populations will be restored in one or more other areas. The overall captive population is likely to remain genetically fragmented in the long term. Individuals will be translocated between sub-populations to maintain gene flow so that the entire population remains a single genetic management unit. When the wild sub-populations have reached the carrying capacity of their respective protected areas, release of head-started animals will be phased out, and they will be left to reproduce naturally. In addition, guided by research and monitoring, control or eradication of non-native predators will be implemented to the degree necessary to allow young Blue Iguanas to survive to maturity in sufficient numbers to maintain these sub-populations.
Maintenance of Blue Iguanas in the wild requires active management into the indefinite future. To sustain this activity, a range of commercial activities generates the funding required, while an ongoing education and awareness effort ensures continued involvement and support by the local community.
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
of the genus Cyclura
Cyclura
Cyclura is a genus of lizards from the family Iguanidae. Members of this genus are known as "cyclurids" or more commonly as rock iguanas and only occur on islands in the West Indies...
endemic to the island of Grand Cayman
Grand Cayman
Grand Cayman is the largest of the three Cayman Islands and the location of the nation's capital, George Town. In relation to the other two Cayman Islands, it is approximately 75 miles southwest of Little Cayman and 90 miles southwest of Cayman Brac.-Geography:Grand Cayman encompasses 76% of...
. Previously listed as a subspecies of the Cuban Iguana
Cyclura nubila
Cyclura nubila, also known as the Cuban rock iguana, Cuban ground iguana, or Cuban iguana, is a species of lizard of the iguana family. It is the largest of the West Indian rock iguanas , one of the most endangered groups of lizards...
, it was reclassified as a separate species in 2004 because of genetic differences discovered four years earlier. The Blue Iguana is one of the longest-living species of lizard (possibly up to 69 years). The record is 67 years.
The Blue Iguana prefers dwelling in rocky, sunlit, open areas in dry forests or near the shore, as the females must dig holes in the sand to lay eggs in June and July. A possible second clutch is laid in September. The Blue Iguana's vegetarian diet includes plants, fruits, and flowers. Its coloration is tan to gray with a bluish cast that is more pronounced during the breeding season and more so in males. It is large and heavy-bodied with a dorsal crest of short spines running from the base of the neck to the end of the tail.
The fossil record indicates that the Blue Iguana was abundant before European colonization; but fewer than 15 animals remained in the wild by 2003, and this wild population was predicted to become extinct within the first decade of the 21st century. The species' decline is mainly being driven by predation
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
by feral pets (cats and dogs) and indirectly by the destruction of their natural habitat
Habitat (ecology)
A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant or other type of organism...
as fruit farms are converted to pasture for cattle grazing. Since 2004, 219 captive-bred animals have been released into a preserve on Grand Cayman run by a partnership headed by the Durrell Wildlife Conservation Trust
Durrell Wildlife Conservation Trust
Durrell Wildlife Conservation Trust is a conservation organisation with a mission to save species from extinction.Gerald Durrell founded the Jersey Wildlife Preservation Trust as a charitable institution in 1963 with the Dodo as its symbol...
, in an attempt to save the species. At least five non-profit organizations are working with the government of the Cayman Islands to ensure the survival of the Blue Iguana.
Taxonomy
The Blue Iguana (Cyclura lewisi) is endemic to the island of Grand Cayman. Its genericGenus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
name (Cyclura
Cyclura
Cyclura is a genus of lizards from the family Iguanidae. Members of this genus are known as "cyclurids" or more commonly as rock iguanas and only occur on islands in the West Indies...
) is derived from the Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
words cyclos (κύκλος) meaning "circular" and ourá (οὐρά) meaning "tail", after the thick-ringed tail characteristic of all Cyclura. Its specific
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
name is a Latinized
Latinisation (literature)
Latinisation is the practice of rendering a non-Latin name in a Latin style. It is commonly met with for historical personal names, with toponyms, or for the standard binomial nomenclature of the life sciences. It goes further than Romanisation, which is the writing of a word in the Latin alphabet...
form of the name of the scientist who first described this species, Bernard C. Lewis. Its closest relatives are the Cuban Iguana (Cyclura nubila) and the Northern Bahamian Rock Iguana
Northern Bahamian Rock Iguana
The Northern Bahamian Rock Iguana is a species of lizard of the genus Cyclura that is found on the Andros and Exuma islands in the Bahamas...
(Cyclura cychlura), the three species having diverged from a common ancestor some three million years ago. The species has a low genetic diversity
Genetic diversity
Genetic diversity, the level of biodiversity, refers to the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary....
but does not seem to suffer the same lack of vitality that afflicts other such species of rock iguana. One theory is that the species evolved from a single female Cuban Iguana (C. nubila nubila) with eggs inside her who drifted
Rafting event
Oceanic dispersal is a type of biological dispersal that occurs when organisms transfer from one land mass to another by way of a sea crossing on large clumps of floating vegetation. Such matted clumps of vegetation are often seen floating down major rivers in the tropics and washing out to sea,...
across the sea, perhaps during a storm. It is distinct from the subspecies found on Little Cayman
Little Cayman
Little Cayman is an island that is part of the Cayman Islands. It is located in the Caribbean Sea, about 75 miles northeast of Grand Cayman and five miles west of Cayman Brac. Little Cayman has a permanent population of less than 170 and is about 10 miles long with an average width of 1 mile...
and Cayman Brac
Cayman Brac
Cayman Brac is an island that is part of the Cayman Islands. It lies in the Caribbean Sea about 90 miles northeast of Grand Cayman and 5 miles east of Little Cayman. It is about 12 miles long, with an average width of 1 mile...
known as C. nubila caymanensis
Cyclura nubila caymanensis
The Lesser Caymans Iguana or Cayman Brac Iguana or Cayman Island Brown Iguana or Sister Isles Iguana is a critically endangered subspecies of the Cuban Iguana...
, although it can breed with this subspecies and produce fertile offspring.
In 1938, Bernard C. Lewis of the Institute of Jamaica joined an Oxford University biological expedition to the Cayman Islands. Lewis was able to obtain two Blue Iguanas, a male and a female, which were later lodged with the British Museum
British Museum
The British Museum is a museum of human history and culture in London. Its collections, which number more than seven million objects, are amongst the largest and most comprehensive in the world and originate from all continents, illustrating and documenting the story of human culture from its...
of Natural History. Chapman Grant
Chapman Grant
Chapman Grant was an American herpetologist, historian, and publisher. He was the last living grandson of United States President Ulysses S. Grant...
, in a monograph published in 1940, formally described the Blue Iguana for the first time as Cyclura macleayi lewisi. Schwartz and Carey established the trinomial
Trinomial nomenclature
In biology, trinomial nomenclature refers to names for taxa below the rank of species. This is different for animals and plants:* for animals see trinomen. There is only one rank allowed below the rank of species: subspecies....
(Cyclura nubila lewisi) in 1977. They held that the Blue Iguana was a strongly distinct subspecies of the Cuban Iguana (C. nubila), the species which it evolved from and can breed with. They emphasized its overall bright blue coloration, and noted that further study could reveal it to be a distinct species. Frederick Burton reclassified the Blue Iguana as a distinct species in 2004, after years of research comparing scale counts on the heads of Caribbean iguanas, including those found on Little Cayman, Cayman Brac, Cuba, and the Bahamas, as well as mitochondrial DNA
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...
analysis performed by Dr. Catherine Malone, to re-examine the phylogeography
Phylogeography
Phylogeography is the study of the historical processes that may be responsible for the contemporary geographic distributions of individuals. This is accomplished by considering the geographic distribution of individuals in light of the patterns associated with a gene genealogy.This term was...
of the different species.
Description
The Blue Iguana is the largest native land animal on Grand Cayman with a total nose-to-tail length of 5 ft (1.5 m) and weighing as much as 30 lb (13.6 kg). Its body length is 20–30 inches (51–76 cm) with a tail equal in length. The Blue Iguana's toes are articulated to be efficient in digging and climbing trees. Although not known to be arboreal, the Blue Iguana has been observed climbing trees 15 feet (4.6 m) and higher. The male is larger than the female by one third of his body size. The mature male's skin color ranges from dark grey to turquoise blue, whereas the female is more olive green to pale blue. Young animals tend to be uniformly dark brown or green with faint darker banding. When they first emerge from the nest the neonates have an intricate pattern of eight dark dorsalDorsum (biology)
In anatomy, the dorsum is the upper side of animals that typically run, fly, or swim in a horizontal position, and the back side of animals that walk upright. In vertebrates the dorsum contains the backbone. The term dorsal refers to anatomical structures that are either situated toward or grow...
chevrons from the crest of their necks to their pelvic area. These markings fade by the time the animal is one year old, changing to mottled gray and cream and eventually giving way to blue as adults. The adult Blue Iguana is typically dark gray matching the karst
KARST
Kilometer-square Area Radio Synthesis Telescope is a Chinese telescope project to which FAST is a forerunner. KARST is a set of large spherical reflectors on karst landforms, which are bowlshaped limestone sinkholes named after the Kras region in Slovenia and Northern Italy. It will consist of...
rock of its landscape. The animal changes its color to blue when it is in the presence of other iguanas to signal and establish territory. The blue color is more pronounced in males of the species. Their distinctive black feet stand in contrast to their lighter overall body color. Male Blue Iguanas have prominent femoral pore
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 other species, both sexes have them, with the males...
s, which are used to release pheromone
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 outside the body of the secreting individual to impact the behavior of the receiving individual...
s. Females have smaller pores and have a less prominent dorsal crest, making the animal somewhat sexually dimorphic
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
.
Eyes and vision
The Blue Iguana's eyes have a golden irisIris (anatomy)
The iris is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. "Eye color" is the color of the iris, which can be green, blue, or brown. In some cases it can be hazel , grey, violet, or even pink...
and red sclera
Sclera
The sclera , also known as the white or white of the eye, is the opaque , fibrous, protective, outer layer of the eye containing collagen and elastic fiber. In the development of the embryo, the sclera is derived from the neural crest...
. They have excellent vision, which allows them to detect shapes and motions at long distances. As Blue Iguanas have only a few rod cell
Rod cell
Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of visual photoreceptor, cone cells. Named for their cylindrical shape, rods are concentrated at the outer edges of the retina and are used in peripheral vision. On...
s, they have poor vision in low-light conditions. At the same time, they have cells
Cone cell
Cone cells, or cones, are photoreceptor cells in the retina of the eye that are responsible for color vision; they function best in relatively bright light, as opposed to rod cells that work better in dim light. If the retina is exposed to an intense visual stimulus, a negative afterimage will be...
called "double cone
Double cone
Double cones , also known as twin cones in some literature, are two cone cells joined together that may also be coupled optically/electrically...
s" which give them sharp color vision and enable them to see ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
wavelengths. This ability is highly useful when basking so the animal can ensure that it absorbs enough sunlight in the forms of UVA and UVB to produce Vitamin D
Vitamin D
Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....
.
Blue Iguanas have evolved a white photosensory organ on the top of their heads called the parietal eye
Parietal eye
A parietal eye, also known as a parietal organ or third-eye or pineal eye, is a part of the epithalamus present in some animal species...
(also known as the third eye, pineal eye or pineal gland). This "eye" does not work the same way as a normal eye as it has only a rudimentary retina and lens and thus, cannot form images. It is however sensitive to changes in light and dark and can detect movement.
Distribution and habitat
Grand Cayman
Grand Cayman is the largest of the three Cayman Islands and the location of the nation's capital, George Town. In relation to the other two Cayman Islands, it is approximately 75 miles southwest of Little Cayman and 90 miles southwest of Cayman Brac.-Geography:Grand Cayman encompasses 76% of...
. Comparison with other Cyclura species in the region strongly suggests that there was once a coastal population of Blue Iguanas which was gradually displaced or extirpated by human settlements and the construction of roads. The Blue Iguana now only occurs inland in natural xerophytic shrubland and along the interfaces between farm clearings, roads, and gardens and closed-canopy dry forest or shrubland. The interior population is believed to have been attracted to agricultural clearings and fruit farms which provide thermoregulatory opportunities, herbaceous browse, fallen fruit, and nesting soil, but this also brought the Blue Iguana into contact with humans and feral animals. Females often migrate to coastal areas to nest.
Blue Iguanas released into the Queen Elizabeth II Botanic Park
Queen Elizabeth II Botanic Park
Queen Elizabeth II Botanic Park is a non-profit outdoor garden and wildlife facility located in the North Side District of Grand Cayman Island in the British West Indies. The park is owned jointly by the Cayman Islands Government and the National Trust for the Cayman Islands, a group dedicated to...
on Grand Cayman were radiotracked in 2004 to determine ranges for each animal. Females were found to occupy territories of 0.6 acre (2,428.1 m²) and males an average of 1.4 acre (5,665.6 m²) with overlap in common territories, indicating that they choose to maintain a population density
Population density
Population density is a measurement of population per unit area or unit volume. It is frequently applied to living organisms, and particularly to humans...
of four to five animals per hectare
Hectare
The hectare is a metric unit of area defined as 10,000 square metres , and primarily used in the measurement of land. In 1795, when the metric system was introduced, the are was defined as being 100 square metres and the hectare was thus 100 ares or 1/100 km2...
.
The Blue Iguanas occupy rock holes and tree cavities, and as adults are primarily terrestrial. Younger individuals tend to be more arboreal. Hatchlings are preyed upon by the native snake Alsophis cantherigerus
Alsophis
Alsophis is a genus of snake in the Colubridae family. They are among those snakes called "racers" and occur throughout the Caribbean. Alsophis snakes are the world’s rarest form of snake, and are currently critically endangered. Alsophis snakes are small rear fanged snakes, proving them harmless...
. The adults have no natural predators but can fall victim to feral dogs. They typically reach sexual maturity at three to four years of age.
Diet and longevity
Like all Cyclura species, the Blue Iguana is primarily herbivorous, consuming leaves, flowers, and fruits from over 45 species of plant. This diet is very rarely supplemented with insect larvae, crabs, slugs, dead birds, and fungi. The iguanas are presented with a special problem for osmoregulationOsmoregulation
Osmoregulation is the active regulation of the osmotic pressure of an organism's fluids to maintain the homeostasis of the organism's water content; that is it keeps the organism's fluids from becoming too diluted or too concentrated. Osmotic pressure is a measure of the tendency of water to move...
: plant matter contains more potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
and as it has less nutritional content per gram, more must be eaten to meet the lizard's metabolic needs. As they are not capable of creating urine more concentrated than their bodily fluids, they excrete nitrogenous wastes as uric acid salts through a salt gland
Salt gland
The salt gland is an organ for excreting excess salts. It is found in elasmobranchs, seabirds, and some reptiles. In sharks, salt glands are found in the rectum, but in birds and reptiles, they are found in or on the skull, in the area of the eyes, nostrils or mouth. In crocodiles, the salt is...
in the same manner as bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s. As a result, they have developed this lateral nasal gland to supplement renal salt secretion by expelling excess potassium and sodium chloride.
Longevity in the wild is unknown but is presumed to be many decades. A Blue Iguana named "Godzilla" captured on Grand Cayman in 1950 by naturalist Ira Thompson was imported to the United States in 1985 by Ramon Noegel and sold to reptile importer and breeder, Tom Crutchfield in 1990. Crutchfield donated Godzilla to the Gladys Porter Zoo
Gladys Porter Zoo
Gladys Porter Zoo is a zoological and botanical park located in Brownsville, Texas. The zoo officially opened on September 3, 1971, and currently averages 375,000 visitors annually. Situated on , the zoo houses about 400 animal species and over 250 tropical and neo-tropical species and subspecies...
in Brownsville
Brownsville, Texas
Brownsville is a city in the southernmost tip of the state of Texas, in the United States. It is located on the northern bank of the Rio Grande, directly north and across the border from Matamoros, Tamaulipas, Mexico. Brownsville is the 16th largest city in the state of Texas with a population of...
, Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
in 1997 and the lizard remained there until its death in 2004. Thompson estimated Godzilla to be 15 years of age at the time of his capture. At an estimated 69 years of age (54 of which were spent in captivity), Godzilla may be the world's longest-living lizard for which there is reliable record. A closely related Lesser Caymans Iguana (C. nubila caymanensis
Cyclura nubila caymanensis
The Lesser Caymans Iguana or Cayman Brac Iguana or Cayman Island Brown Iguana or Sister Isles Iguana is a critically endangered subspecies of the Cuban Iguana...
) has been documented as living 33 years in captivity.
Reproduction
Mating occurs from May through June. Copulation is preceded by numerous head-bobs on the part of the male, who then circles around behind the female and grasps the nape of her neck. He then attempts to restrain the female in order to maneuver his tail under hers to position himself for intromission. Copulation generally lasts from 30 to 90 seconds, and a pair is rarely observed mating more than once or twice a day. A clutch of anywhere from 1 to 21 eggs are usually laid in June or July depending on the size and age of the female, in nests excavated in pockets of earth exposed to the sun. Several exploratory nests are begun before one is completed. These burrows can range from 16 inch (0.4064 m) to over 60 inches (1.5 m) in length, with an enlarged chamber at its terminal portion to allow the female to turn around. The temperature within nests that have been monitored by researchers remained a constant 32 °C (89.6 °F) throughout the incubation period which ranges from 65–90 days. The Blue Iguana's eggs are among the largest laid by any lizard.Individuals are aggressively territorial from the age of about three months onward. Females occupy overlapping areas of the order of 0.6 acre (2,428.1 m²) seemingly regardless of age, while males occupy progressively larger and more extensively overlapping territories as they age and grow.
Endangered status
IUCN Red List
The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...
. The population is restricted to the eastern interior of Grand Cayman, where it had been reduced to a critically low level, only three animals having been observed before the survey in 1988. The range of the Blue Iguana has contracted significantly over the past 25 years, with many sites once populated now showing no signs of iguanas. Surveys in 2003 indicated a total population in the range of 5–15 individuals. By 2005 the unmanaged wild population was considered to be functionally extinct. The species is one of the most endangered animals on Earth. A further blow to the dwindling population came in May 2008 when six individuals were found butchered in a nature preserve.
As the Blue Iguana consumes a variety of plant material, favoring fruits and flowers over leaves and stems when available, it is valuable on Grand Cayman as a seed disperser throughout its range. A study in 2000 by Dr Allison Alberts revealed that seeds passing through the digestive tracts of Cycluras germinate more rapidly than those that do not. These seeds in the fruits consumed by the Blue Iguana have an adaptive advantage by sprouting before the end of very short rainy seasons. The Blue Iguana is also an important means of distributing seeds to new areas and, as the largest native herbivore of Grand Cayman's ecosystems, it is essential for maintaining the delicate balance between climate and vegetation necessary to survive under harsh conditions.
Restored free-roaming subpopulations in the Queen Elizabeth II Botanic Park and the Salina Reserve numbered approximately 125 individuals in total after a release in December 2005. The restored subpopulation in the Queen Elizabeth II Botanic Park has been breeding since 2001, and the subpopulation in the Salina Reserve was deemed to be breeding in 2006 after a nest of three hatched eggs was discovered in the wild. As of April 2007, after another large-scale release, there are 299 Blue Iguanas living in the wild, with hundreds more being raised in captivity on Grand Cayman.
Causes of decline
Habitat destruction is the main factor threatening imminent extinction for this iguana. Land clearance within remnant habitat is occurring for agriculture, road construction, and real estate development and speculation. Conversion of traditional crop lands to cattle pasture is also eliminating secondary Blue Iguana habitat.Predation and injury to hatchlings by rat
Rat
Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus...
s, to hatchlings and sub-adults by feral cat
Feral cat
A feral cat is a descendant of a domesticated cat that has returned to the wild. It is distinguished from a stray cat, which is a pet cat that has been lost or abandoned, while feral cats are born in the wild; the offspring of a stray cat can be considered feral if born in the wild.In many parts of...
s, and killing of adults by roaming dogs
Pariah dog
The term pariah dog originally referred to Chinese/Indian feral dogs of a particular type, but it is now used by the United Kennel Club to refer to a purebred dog category.- Feral dogs of India :...
are all placing severe pressure on the remaining wild population. Automobiles and motorscooters are an increasing cause of mortality as the iguanas rarely survive the collisions. Trapping and shooting is a comparatively minor concern, but occasional trapping continues despite legal protection and sustained efforts to increase public awareness.
The common Green Iguana
Green Iguana
The Green Iguana or Common Iguana is a large, arboreal herbivorous species of lizard of the genus Iguana native to Central and South America...
, (Iguana iguana), has been introduced from Honduras
Honduras
Honduras is a republic in Central America. It was previously known as Spanish Honduras to differentiate it from British Honduras, which became the modern-day state of Belize...
and is well-established on Grand Cayman as an invasive species
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
. It far outnumbers the endemic Blue Iguana. No direct negative consequences of this introduction on the Blue Iguana are known, but the mere presence of the Green Iguana confuses public attitudes and understanding. For example, the people of the island are told that Blue Iguanas are endangered and rare, and when they subsequently see large numbers of the introduced Green Iguana, they do not understand the difference.
Blue Iguanas used to regularly be sold to tourists as pets, as their rarity made them appealing to exotic-animal collectors, despite this being illegal under the CITES treaty. In 1999 a World Wildlife Fund international conservation officer, Stuart Chapman, said, "The British government has turned a blind eye for over 20 years to these overseas territories which are home to many rare and endangered species. Many of these face extinction if Britain fails to honour its treaty obligations. The British Caribbean islands are extremely rich in biodiversity with many critically endangered species
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
that are unique to the islands—yet there is virtually zero enforcement or implementation of CITES."
In May 2008, six Blue Iguanas were found dead in the preserve within Queen Elizabeth II Botanic Park on Grand Cayman. The iguanas were apparently killed by human vandals armed with knives and two of the slaughtered animals were gravid females about to lay eggs.
The wild population of Blue Iguanas had been reduced from a near island-wide distribution to a non-viable, fragmented remnant. By 2001, no young hatched in the unmanaged wild population were surviving to breeding age, meaning the population was functionally extinct, with only five animals remaining in the wild.
Recovery efforts
In 1990 the American Zoo and Aquarium Association (AZA) designated the genus Cyclura as their highest priority for conservation. Their first project was an in situIn situ
In situ is a Latin phrase which translated literally as 'In position'. It is used in many different contexts.-Aerospace:In the aerospace industry, equipment on board aircraft must be tested in situ, or in place, to confirm everything functions properly as a system. Individually, each piece may...
captive breeding program for the Blue Iguana, which at the time was the most critically endangered of all the species of Cyclura.
One of the early difficulties encountered was that the captive stock of the early 1990s was found not to be pure. It was discovered through DNA analysis that the captive population contained a number of animals that were hybrids with C. nubila caymanensis. The program contains only pure specimens, as these hybrids were sterilized by means of hemipenectomies and hence excluded. This program was created to determine the exact genealogies of the limited gene pool of the remaining animals and DNA analysis revealed that the entire North American captive population was descended from a single pair of animals. After five years of research two captive breeding populations were established and are managed as a single unit, with cross-breeding between the populations to promote genetic diversity.
As a hedge against disaster striking the Blue Iguana population on Grand Cayman, an off-island captive population was established in 25 zoos in the USA. A minimum of 20 founder lines represented by at least 225 individuals is being maintained by captive breeding and recorded in a studbook for the species by Tandora Grant of the San Diego Zoo
San Diego Zoo
The San Diego Zoo in Balboa Park, San Diego, California, is one of the most progressive zoos in the world, with over 4,000 animals of more than 800 species...
's Center for Conservation and Research for Endangered Species (CRES). The Indianapolis Zoo
Indianapolis Zoo
The Indianapolis Zoo in Indianapolis, Indiana, United States, first opened to the public in 1964. Its current home in White River State Park was opened in 1988 with a size of . The zoo hosts more than a million visitors each year and plays a role in worldwide conservation and research, including...
has had success with breeding the Blue Iguana in captivity twice since the year 2000.
In October 2006, hatchlings were released into the wild for the first time to boost the species and help bring them back from the brink of extinction. Each released Blue Iguana wears a string of colored beads through its nuchal
Neck
The neck is the part of the body, on many terrestrial or secondarily aquatic vertebrates, that distinguishes the head from the torso or trunk. The adjective signifying "of the neck" is cervical .-Boner anatomy: The cervical spine:The cervical portion of the human spine comprises seven boney...
crest for visual identification at a distance, backed up by an implanted microchip
Microchip implant (animal)
A microchip implant is an identifying integrated circuit placed under the skin of a dog, cat, horse, parrot or other animal. The chips are about the size of a large grain of rice and are based on a passive RFID technology....
and a high-resolution photograph of its head scales. (Head scale patterns are as unique among Blue Iguanas as fingerprints are among humans.)
The Blue Iguana is established in captivity, both in public and private collections. As there are very few pure-bred animals in private collections, private individuals have established these animals in captive breeding programs as hybrids with the Lesser Caymans Iguana (C.nubila caymanensis) and occasional hybrids with the Cuban Iguana (C.n.nubila) minimizing the demand for wild-caught specimens for the pet trade.
Blue Iguana Recovery Programme
The Blue Iguana Recovery Programme grew from a small project started within the National Trust for the Cayman Islands in 1990. It is now a partnership, linking the Trust with the Cayman Islands Department of Environment, National Trust Cayman Islands, Queen Elizabeth II Botanic Park, Durrell Wildlife Conservation TrustDurrell Wildlife Conservation Trust
Durrell Wildlife Conservation Trust is a conservation organisation with a mission to save species from extinction.Gerald Durrell founded the Jersey Wildlife Preservation Trust as a charitable institution in 1963 with the Dodo as its symbol...
, International Reptile Conservation Foundation, IRCF, and the European Commission
European Commission
The European Commission is the executive body of the European Union. The body is responsible for proposing legislation, implementing decisions, upholding the Union's treaties and the general day-to-day running of the Union....
. This program operates under a special exemption from provisions in the Animals Law of the Cayman Islands which normally would make it illegal for anyone to kill, capture, or keep iguanas. BIRP's conservation
Wildlife conservation
Wildlife conservation is the preservation, protection, or restoration of wildlife and their environment, especially in relation to endangered and vulnerable species. All living non-domesticated animals, even if bred, hatched or born in captivity, are considered wild animals. Wildlife represents all...
strategy involves generating large numbers of genetically diverse hatchlings, head-starting them for two years where their chance of survival in the wild is high, and using these animals to rebuild a series of wild sub-populations in protected, managed natural areas. This is accompanied by field research, nest site protection, and monitoring of the released animals. A rapid numerical increase from a maximum possible number of founding stock is sought to minimize loss of genetic diversity caused by the "population bottleneck
Population bottleneck
A population bottleneck is an evolutionary event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing....
".
Restored sub-populations are already present in two non-contiguous areas—the Salina Reserve and the Queen Elizabeth II Botanic Park. Habitat protection is still vital, as the Salina Reserve has only 88 acre (356,123.7 m²) of dry shrubland, which is not enough to sustain the 1,000 Blue Iguanas that must be restored to the wild to remove this species from the Critically Endangered List. Additional separate sub-populations will be restored in one or more other areas. The overall captive population is likely to remain genetically fragmented in the long term. Individuals will be translocated between sub-populations to maintain gene flow so that the entire population remains a single genetic management unit. When the wild sub-populations have reached the carrying capacity of their respective protected areas, release of head-started animals will be phased out, and they will be left to reproduce naturally. In addition, guided by research and monitoring, control or eradication of non-native predators will be implemented to the degree necessary to allow young Blue Iguanas to survive to maturity in sufficient numbers to maintain these sub-populations.
Maintenance of Blue Iguanas in the wild requires active management into the indefinite future. To sustain this activity, a range of commercial activities generates the funding required, while an ongoing education and awareness effort ensures continued involvement and support by the local community.