The Lesser Antillean Iguana (Iguana delicatissima) on St. Eustatius: Genetically Depauperate and Threatened by Ongoing Hybridization

Abstract

The Lesser Antillean Iguana (Iguana delicatissima) is an endangered species threatened by habitat loss and hybridization with non-native Green Iguanas (Iguana iguana). Iguana delicatissima has been extirpated on several islands, and the Green Iguana has invaded most islands with extant populations. Information is essential to protect this species from extinction. We collected data on 293 iguanas including 17 juveniles from St. Eustasius, one of the few remaining I. delicatissima strongholds. Genetic data were leveraged to test for hybridization presence with the Green Iguana using both mitochondrial and nuclear genes, including 16 microsatellite loci. The microsatellites were also analyzed to estimate genetic diversity, population structure, and effective population size. Using molecular and morphological data, we identified 286 I. delicatissima individuals captured during our first fieldwork effort, and 7 non-native iguanas captured during a second effort, showing hybridization occurs within this population. Comparing homologous microsatellites used in studies on Dominica and Chancel, the I. delicatissima population on St. Eustatius has extremely low genetic diversity (HO = 0.051; HE = 0.057), suggesting this population is genetically depauperate. Furthermore, there is significant evidence for inbreeding (FIS = 0.12) and weak spatial genetic structure (FST = 0.021, P = 0.002) within this population. Besides immediate threats including hybridization, this population's low genetic diversity, presence of physiological abnormalities and low recruitment could indicate presence of inbreeding depression that threatens its long-term survival. We conclude there is a continued region-wide threat to I. delicatissima and highlight the need for immediate conservation action to stop the continuing spread of Green Iguanas and to eliminate hybridization from St. Eustatius.

Painted black: Iguana melanoderma (Reptilia, Squamata, Iguanidae) a new melanistic endemic species from Saba and Montserrat islands (Lesser Antilles)

“…The difficulty lies mainly in the different concepts used to distinguish between the species and subspecies categories (Torstrom et al 2014). Hybridization is known between the endemic iguanas of the Lesser Antilles and the two invasive lineages i.e., Iguana iguana and Iguana rhinolopha (Breuil , 2016Vuillaume et al 2015) and now with the Curacao lineage in Saint Maarten (Van den Burg et al 2018a, 2018b. In addition, hybridization has recently occurred between endemic Cyclura nubila and Iguana iguana (Moss et al 2018).…”

“…As the range of invasive iguanas increases worldwide (Falcón et al 2013), and mainly in the Caribbean (Powell et al 2011;van den Burg et al 2018avan den Burg et al , 2018b, the probability of invasive iguanas arriving on Saba increases with trade, travel, and tourism on St. Maarten (Yokoyama 2012), another Dutch island 45 km north of Saba. It is thus necessary to conserve these original populations and to be able to differentiate them from invasive iguanas of different lineages.…”

“…The same phenomenon is underway in Basse-Terre and St. Barthélemy leading to the further decline of Iguana delicatissima (Vuillaume et al 2015;Breuil , 2016. Since these recent studies, hybridization between these two species is known to have occurred in Martinique, La Désirade (MB, unpublished results), and St. Eustatius (Van den Burg et al 2018a;2018b). Thus, a natural cline concerning, for example, the size of the tubercular nape scales as advocated by Lazell (1973), cannot exist with only two groups of iguanas naturally present.…”

Harmonizing hybridization dissonance in conservation

“…56 . Fifth, hybridization may affect the effective population size of the interacting species with major consequences for rare or threatened species, which already have a reduced number of breeders 57 . Finally, an important problem for conservation biology arises when the few remaining individuals of a threatened species show a level of introgression that may cause them to lose their legal protection status when hybrids are not considered to be protected organisms, even though the hybrids may have an ecological function otherwise lost with the extinction of parental species 21,58 .…”

Hurricane-induced population decrease in a Critically Endangered long-lived reptile

“…Among Caribbean Iguanids, the conservation status of the Lesser Antillean iguana ( Iguana delicatissima ) has experienced the most rapid deterioration (van den Burg et al 2018a). Its pre-Colombian range has to date decreased by >80%, predominantly due to hybridization with Iguana iguana lineages (Vuillaume et al 2015; Pounder et al 2020), a process that was recently initiated on the last remaining ≥2 km 2 islands where I. delicatissima occurs (van den Burg et al 2018b, 2020; B. Angin pers. comm.).…”