The Saban black iguana (Iguana iguana melanoderma) is a subspecies (sometimes considered a distinct species) of the green iguana thought to be endemic to the islands of Saba and Montserrat, although external evidence indicates that it may be distributed in other parts of the Caribbean. It was described in 2020 as a distinct species, although the Reptile Database classifies it as a subspecies of the common green iguana (Iguana iguana).[1]
The subspecies was previously considered to represent melanistic individuals of the green iguana. It was reclassified as a separate subspecies based on a number of genomic distinctions (private microsatellite alleles and unique mitochondrial ND4 haplotypes) and consistent morphological characteristics.[2] Genetic evidence indicates that I. i. melanoderma is the sister group of the green iguana populations from South America (considered I. iguana iguana), with both forming a clade that is the sister group of the green iguana populations present on St. Lucia and the Grenadines, which are considered a distinct subspecies, I. i. insularis.[3] The Reptile Database also recognizes the Saban black iguana as a distinct taxonomic entity, but due to its close relation to the green iguana, it (along with the two subspecies of I. insularis) is instead classified as a subspecies of the green iguana, as I. i. melanoderma.
As proposed in the original publication, the subspecies displays a very unusual disjunct distribution. Member populations are found on Montserrat and Saba, as well as on the Virgin Islands and the island of Vieques, and in northern Venezuela, including several coastal islets as well as the mainland vicinity of Cumaná. The mainland distribution has not been well defined. A news article indicated that it is believed the species was also present on Redonda, but this was not addressed in the original publication; several authors have mentioned having seen iguanas, but no specimens have been collected, nor any fossils identified. Recent genetic insights confirm that near-indistinguishable melanistic iguanas (compared to Saba and Montserrat) have identical mitohondrial haplotypes as those two populations in the Lesser Antilles.[4] Genetic data remains to be analyzed from the populations assigned to this subspecies in Venezuela.It is theorized that coastal Venezuela is the source population for I. i. melanoderma and also where it diverged from other iguanas. Three dispersal events have been proposed; one from coastal Venezuela to either Saba or Montserrat (with Montserrat being more likely if the dispersal was natural), a second pre-Columbian dispersal from one of these two islands to the other, and a third to Puerto Rico and the Virgin Islands. These dispersal events may have happened from natural dispersals, transport and introduction by Amerindians and/or European colonists, or both. As parts of its range may have been facilitated by human transport, its strange disjunct distribution may not be entirely natural in origin.
A 2022 population estimate on Saba suggests that ~6000 iguanas occur on the island.