Breuil, M.

The Lesser Antilles, in the Eastern Caribbean, is inhabited by three Iguana species: the Lesser Antillean iguana Iguana delicatissima, which is endemic to the northernmost islands of the Lesser Antilles, the introduced common iguana from South America, Iguana iguana iguana, represented also by the two newly described endemic subspecies Iguana iguana sanctaluciae from Saint Lucia and Iguana iguana insularis from Saint Vincent and the Grenadines, and Grenada, and the introduced Iguana rhinolopha from Central America. Drawing on both morphological and genetic data, this paper describes the Iguana populations from Saba and Montserrat as a new species, Iguana melanoderma. This species is recognized on the basis of the following combination of characteristics: private microsatellite alleles, unique mitochondrial ND4 haplotypes, a distinctive black spot between the eye and tympanum, a dorsal carpet pattern on juveniles and young adults, a darkening of body coloration with aging (except for the anterior part of the snout), a black dewlap, pink on the jowl, the high number of large tubercular nape scales, fewer than ten medium sized–triangular dewlap spikes, high dorsal spikes, and lack of horns on the snout. This new melanistic taxon is threatened by unsustainable harvesting (including for the pet trade) and both competition and hybridization from escaped or released invasive alien iguanas (I. iguana iguana and I. rhinolopha) from South and Central America, respectively. The authors call for action to conserve Iguana melanoderma in Saba and Montserrat and for further research to investigate its relationship to other melanistic iguanas from the Virgin Islands and coastal islands of Venezuela.

Keywords

Conservation Biology, Iguana, Lesser Antilles, microsatellites, mtDNA, new endemic species, phylogeny

Taxon Name: Iguana delicatissima Laurenti, 1768

Common Name(s):

• English: Lesser Antillean Iguana, West Indian Iguana

• French: Iguane des Petites Antilles

Assessment Information

Red List Category & Criteria: Critically Endangered

Year Published: 2018
Date Assessed: March 3, 2018

Justification:

Based on historic range data and an estimated index of abundance, the total population has experienced declines of ≥ 75%. Although extirpation from some islands occurred in the early to mid- 20th century, the remaining population has continued to decline within the last three generations (33–42 years). In recent years, on-going decline and extirpation of the Lesser Antillean Iguana has been primarily caused by inter- and intra-island dispersal of the invasive alien Common Green Iguana and subsequent hybridization. Common Green Iguanas are much more vigorous reproductively compared to native Lesser Antillean Iguanas, and hybridization and displacement is rapid post-introduction. Since the last assessment (2010), Common Green Iguanas have been observed among three additional pure populations (St. Eustatius, La Désirade, Ramiers), including the site of a recent native iguana reintroduction detailed in the previous regional action plan. These dispersals have not been mitigated and there is no likelihood of containing these threats without more proactive management. The current AOO of the species is estimated at less than 1,000 km2, the existing subpopulations are fragmented among isolated locations, and the large majority of the current range exists on one island (Dominica).

Population numbers for all islands is not available for multiple past generations, however their former area of occupancy can be estimated from published observations and an estimate of abundance based on habitat availability and quality. To project future population reductions, an annual rate of decline in AOO was calculated from the islands invaded by Common Green Iguana, from the known date of invasion to the present, and the remaining area occupied by pure subpopulations. Rates were applied to similarly-sized islands and assuming the worst-case scenario of invasion of remaining pure populations within the next few years. It is strongly felt the risk of invasion and extirpation of the remaining pure populations is imminent in the wake of increased post-hurricane shipping among islands in both species’ range, and the lack of biosecurity to mitigate this threat. The recent increase in illegal poaching is also a significant threat to the species’ persistence.

Under these projection parameters, within one generation, five of the remaining pure populations plus four of the currently invaded/hybridized locations will be extirpated. Only 13% of the species’ current AOO is predicted to remain three generations from now.

This is a genuine change from the most recent assessment due to increasing occurrence and rate of hybridization and island extirpations.