New Species Of Melanistic Black Iguana Discovered in The Caribbean

A basking iguana optimizing after different trials its warming by a curved position when the sun is low on the horizon on the Windward coast of Saba. M. Breuil

Madison Dapcevich 15 Apr 2020, 11:18

A newly discovered species of black iguana found in the Eastern Caribbean may already be facing threats from unsustainable harvesting and invasive iguanas, new research suggests.

Iguana melanoderma is morphologically and genetically different than the other two endemic species of green iguana known to the area. Found on the islands of Saba and Montserrat, it is named for its melanism, a genetic mutation of the cells that regulate the color of hair and skin, whereby high concentrations of the dark pigment melanin results in nearly all-black coloring. Melanism most often occurs in panthers but has resulted in the wild coloring of species across the animal kingdom, like this polka-dot zebraall-black penguin, and playful coyote.

Researchers identified the new species by observing individuals in the wild, as well as photographs of them, and comparing them with specimens at various research institutions. DNA was extracted from 44 individuals to confirm their findings, which are described in the journal ZooKeys. Characterized by a distinctive black spot between the reptile’s eye and ear cavity, or tympanum, the juveniles and young adults have a “slight carpet pattern” that eventually darkens as the animal ages.

On the island of Saba, I. melanoderma is considered a “flagship species” and lounges on cliffs, particularly in foggy and cool environments where they can be found sunbathing as the Sun rises. On the nearby volcanic island of Montserrat, the iguanas can be found in a variety of habitats, including residential areas, but prefer locations near the cooler waters of streams and rivers. Researchers propose that the black coloration could be an adaptation to help the reptiles raise their body heat in cooler conditions.

Comparison of morphological features of the heads of a juvenile and adult specimen. ZooKeys

At least three other iguana species are known to occur in the region, including the Lesser Antillean iguana (Iguana delicatissima) endemic to northernmost islands of the Caribbean. Two introduced species, the common iguana (Iguana iguana iguana) from South America and the green iguana (Iguana rhinolopha) from Central America, have outcompeted and interbred with native species – a conservation concern researchers say could threaten I. melanoderma.

"With the increase in trade and shipping in the Caribbean region and post-hurricane restoration activities, it is very likely that there will be new opportunities for invasive iguanas to colonize new islands inhabited by endemic lineages," said lead researcher Frédéric Grandjean from the University of Poitiers in a statement.

The green iguana is classified as a species of “least concern” and because I. melanoderma is not differentiated under the International Union for Conservation of Nature (IUCN) Red List of Species, the researchers argue that the newly revealed black species may be at risk of threats not considered by the conservation organization.

"Priority actions for the conservation of the species Iguana melanoderma are biosecurity, minimization of hunting, and habitat conservation. The maritime and airport authorities of both islands must be vigilant about the movements of iguanas, or their sub-products, in either direction, even if the animals remain within the same nation's territory. Capacity-building and awareness-raising should strengthen the islands' biosecurity system and could enhance pride in this flagship species," concluded Grandjean.

The dorsal carpet pattern of young adults Iguana melanoderma from Montserrat (top) and Saba (bottom). The dorsal coloration is formed by darker bands of brown and dark grey on a lighter ground, which disappears in old individuals. ZooKeys

 

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