Rhinoceros iguana

The rhinoceros iguana (''Cyclura cornuta'') is an endangered species of iguana that is endemic to the Caribbean island of Hispaniola (shared by Haiti and the Dominican Republic) and its surrounding islands. A large lizard, they vary in length from , and skin colours range from a steely grey to a dark green and even brown. Their name derives from the bony-plated pseudo-horn or outgrowth which resembles the horn of a rhinoceros on the iguana's snout. It is known to coexist with the Ricord's iguana (''C. ricordii''); the two species are the only taxa of rock iguana to do so.

Taxonomy

The rhinoceros iguana is a species of lizard belonging to the genus ''Cyclura''. The rhinoceros iguana's specific name, ''cornuta'', is the feminine form of the Latin adjective ''cornutus'', meaning "horned" and refers to the horned projections on the snouts of males of the species. The species was first identified by Pierre Joseph Bonnaterre in 1789.

In addition to the nominate race (''C. c. cornuta'') found on Hispaniola, the other subspecies is the extinct Navassa Island iguana (''C. c. onchiopsis''). The Mona ground iguana (''Cyclura stejnegeri'') from Puerto Rico was originally thought to be a subspecies (and still is by some taxonomists), as ''Cyclura cornuta stejnegeri''.

Anatomy and morphology

The rhinoceros iguana, like other members of the genus ''Cyclura'', is a large-bodied, heavy-headed lizard with strong legs and a vertically flattened tail. A crest of pointed horned scales extends from the nape of their neck to the tip of their tail. Their color is a uniform gray to brown drab. Most adults weigh . Like all reptiles, rhinoceros iguanas are cold-blooded, meaning they need external sources to heat themselves; they move as the sun shifts in order to get an optimal internal temperature.

These iguanas are characterized by the growth of bony prominent tubercles on their snouts which resemble horns. Males possess an adipose pad in the form of a helmet on the occipital region of the head, and a large dewlap. This species, like other species of ''Cyclura'', is sexually dimorphic; males are larger than females, and have more prominent dorsal crests and "horns" in addition to large femoral pores on their thighs, which are used to release pheromones.

Distribution and habitat

Ranging throughout Hispaniola (in both Haiti and the Dominican Republic), rhinoceros iguana populations are stable only on Isla Beata, and the extreme of the Barahona Peninsula, inside Jaragua National Park. There are moderately dense populations in the southeastern region of Haiti and its offshore islands, including the brackish lake of Étang Saumâtre, as well as the Dominican hypersaline Lake Enriquillo and its lake island, Isla Cabritos. Populations in Haiti are even more endangered due to deforestation, poaching for bushmeat, and human clearing practices. In general, the iguanas are found most abundantly in (although not restricted to) scrub woodland in Hispaniolan dry forests, which are characterized by xeric, rocky habitats of eroded limestone in coastal terraces and lowlands of the mainland, and several offshore islands and small cays in a variety of subtropical life zones and habitat types. The biome that the rhinoceros iguanas live in are ones that receive very little rain with little trees and shrubs. This species has been known to exhibit phenotypic plasticity like other iguanas. While historically present near coastlines, human activity and introduced predators have forced rhinoceros iguanas inland.

An individual was photographed on May 4, 2008 on Limbe Island in northern Haiti. It had been caught by a group of fishermen from Bas-Limbe, Bord de Mer village. The rhinoceros iguanas caught on Limbe Island are illegally eaten by the local population. This sighting represents a new area previously not thought to be in the range of ''C. cornata''.

Aside from Hispaniola and its surrounding islands, the rhinoceros iguana was previously found on Navassa Island (with an endemic subspecies: ''C. c. onchiopsis''), but was extirpated there.

Behaviour

Rhinoceros iguanas, like most members of ''Cyclura'', are usually docile and well-tempered. Although quick to flee when attacked or threatened, they will aggressively attack by biting and repeatedly striking with their thick tail if cornered.

Diet

The rhinoceros iguana, like most ''Cyclura'' species, is primarily herbivorous, consuming leaves, flowers, berries, and fruits from different plant species. A study in 2000 by Dr Allison Alberts of the San Diego Zoo revealed that seeds passing through the digestive tracts of ''Cyclura'' species germinate more rapidly than those that do not. These seeds in the fruits consumed by cycluras have an adaptive advantage by sprouting before the end of very short rainy seasons. The rhinoceros iguana is also an important means of distributing these seeds to new areas (particularly when females migrate to nesting sites) and, as the largest native herbivores of their island's ecosystem, they are essential for maintaining the balance between climate and vegetation. Rhinoceros iguanas do appear to be opportunistic carnivores, as individual animals have been observed eating small lizards, snakes, and insects.

Ecology

The rhinoceros iguana's only confirmed native predator is the Hispaniola racer (''Haitiophis anomalus''), a large snake which has been recorded to give chase to juvenile iguanas, as well as wait for them outside the exit holes of their burrow.Landestoy T., Miguel & Henderson, Robert & Rupp, Ernst & Marte, Cristian & Ortiz, Robert. (2013). Notes on the Natural History of the Hispaniolan Brown Racer, Haitiophis anomalus (Squamata: Dipsadidae), in the Southern Dominican Republic. IRCF REPTILES & AMPHIBIANS. 20. 130-139. Accessed at https://www.researchgate.net/publication/284550279_Notes_on_the_Natural_History_of_the_Hispaniolan_Brown_Racer_Haitiophis_anomalus_Squamata_Dipsadidae_in_the_Southern_Dominican_Republic. However, most predation of iguanas comes from invasive species like feral dogs (''Canis familiaris''), feral cats (''Felis catus''), small Indian mongooses (''Urva auropunctata''), and feral pigs (''Sus domesticus''), which all feed on eggs, adults, and juveniles.

Mating and reproduction

Male rhinoceros iguanas, unlike other members of the genus ''Cyclura'', reach sexual maturity at four to five years of age. Females become sexually mature at two to three years of age. Male rhinoceros iguanas are territorial and the most aggressive males will have the largest range of territory. Mating takes place at the beginning of, or just prior to, the first rainy season of the year (May to June) and lasts for two to three weeks. Females lay from 2 to 34 eggs, with an average clutch size of 17, within 40 days. Females guard their nests for several days after laying their eggs, and incubation lasts approximately 85 days.

Notably, despite rhinoceros iguanas exhibiting some sexual dimorphism in size and horn development, they exhibit comparatively less sexual dimorphism than most other iguanas. Both male and female rhinoceros iguanas lack prominent mid-dorsal spines on their neck, which are typically very large in male iguanas of other species, both have well-developed dewlaps, and both develop horns. By contrast, in many other animals that exhibit horns such as ungulates or rhinoceros beetles, horns are often only present in males. Rhinoceros iguanas are also reported to show less dimorphism in size than other iguana species. This reduced dimorphism has been suggested to be due to intense female-female competition in rhinoceros iguanas, given the scarcity of nesting sites in their island environment, and females will use their horns to fight with one another over access to nesting sites much as males fight for access to females. Similar female-female combat over nesting sites has been documented in other island iguanas such as the marine iguana.

Conservation

Although rhinoceros iguanas are the most common species of ''Cyclura'' kept in captivity, approximately 10,000-16,000 iguanas remain in the wild. A successful breeding program existed at the Parque Zoológico Nacional of the Dominican Republic (ZooDom) from 1974 to 1994, with an average of 100 babies hatching annually. These efforts included reintroductions of captive-bred "head-started" young to several protected areas in the southwest Dominican Republic, in order to reduce the odds of predation by snakes and introduced carnivorans, such as mongooses or feral cats and dogs. The program has not continued since 1995, due to an administrative change at the zoo. International trade in the species is regulated under the Appendix I of the Convention on International Trade in Endangered Species. Illegal logging, competition from domestic grazers (cows, pigs, goats), predation on young by invasive species, limestone mining, harvesting for the pet trade, hunting for bushmeat, pollution, and wildfires are all manmade threats to the rhinoceros iguana's survival.

Captivity

The rhinoceros iguana is well established in captivity, both in public and private collections. As of 2007, rhinoceros iguanas were present in captivity throughout the United States (total 39 males, 32 females, and 36 undetermined individuals) at 20 zoological institutions, with an additional 533 animals of unassigned subspecies, reported by seven American Zoological and Aquarium Association institutions. The actual number may be much higher, considering animals kept at European and Asian zoos, and the amount kept as pets in private collections. As a result, the demand for wild-caught animals to supply zoos and the pet trade has been reduced.

Gallery

References

External links

Profile on Cyclura.comIguana at PhotoSig.comIguanario de los Tocones, Dominican Republic

{{Taxonbar, from=Q907252

Cyclura
iguana, Rhinoceros
Endemic fauna of Hispaniola
Reptiles of Haiti
Reptiles of the Dominican Republic
Reptiles described in 1789
Taxa named by Pierre Joseph Bonnaterre
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