Testing for hybridisation of the Critically Endangered Iguana delicatissima on Anguilla to inform conservation efforts

Abstract

The Caribbean Island of Anguilla in the northeastern Lesser Antilles is home to one of the last populations of the Critically Endangered Lesser Antillean iguana Iguana delicatissima. This population is highly threatened primarily because of hybridisation with non-native Iguana iguana. This study assesses the degree of hybridisation between Anguilla's Iguana species firstly using morphological characteristics and then genetic analysis to validate the genetic integrity of morphologically identified I. delicatissima. We also examined the genetic diversity of Anguilla's I. delicatissima population, and that of a population on the nearby island of Îlet Fourchue, St Barthélemy. Forty-five iguanas were captured in Anguilla and 10 in St Barthélemy, and sequences from 3 nuclear and 1 mtDNA genes were obtained for each. Of the 45 iguanas captured in Anguilla, 22 were morphologically identified as I. delicatissima, 12 as I. iguana and the remainder were identified as hybrids. Morphological assignments were all confirmed by genetic analyses except for one I. iguana and one hybrid individual. These two individuals appeared likely to have originated following ancestral hybridisation events several generations ago. A significant paucity of genetic diversity was found within Anguillan and St Barthélemy I. delicatissima populations, with a single haplotype being identified for each of the three nuclear genes and the mtDNA sequence. This study highlights the urgency for immediate action to conserve Anguilla's remnant I. delicatissima population. Protection from hybridisation will require translocation to I. iguana-free offshore cays, with supplementary individuals being sourced from neighbouring islands to enhance the genetic diversity of the population.

Iguana insularis (Iguanidae) from the southern Lesser Antilles: An endemic lineage endangered by hybridization

“…As a result of both deliberate and accidental transportation, invasive alien iguanas (I. iguana and I. rhinolopha) and their fertile hybrids are now widely scattered across the Eastern Caribbean and pose a serious threat to all remaining indigenous populations of I. insularis, I. melanoderma and I. delicatissima (Breuil et al 2019(Breuil et al , 2020Pounder et al 2020;van den Burg et al 2018;Breuil 2021). Indeed, a number of populations have already been lost following incursions by invasive alien Iguana species, e.g., I. delicatissima from most of Guadeloupe after the arrival of I. iguana (Vuillaume et al 2015).…”

“…Similar observations were reported by Breuil et al (2019) in one specimen of I. insularis insularis on Union Island that harbored a South American mitochondrial haplotype (based on the analyze of the ND4 loci MK687401). Introgression is already a well-known phenomenon in iguana populations, notably between I. iguana and I. delicatissima in Guadeloupe and Anguilla and between I. rhinolopha and I. delicatissima in St. Barthélemy (Breuil , 2016Vuillaume et al 2015;Pounder et al 2020) andSt. Eustatius (van den Burg et al 2018).…”

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

“…Our study further highlights this vulnerability, as local extinction or population declines to unsustainable sizes could be the result of major hurricanes. Especially the extremely small population of Anguilla is vulnerable (Pounder et al 2020), which currently occurs on a small low-level islet. There, the potential of temporarily holding iguanas to increase hurricane survival should be assessed, given adequate facilities can be utilized.…”

“…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.).…”

“…Left uncontrolled, the genetic loss of these populations will lead to a >99% decrease in their native range (van den Burg et al 2018a). Critically, the five remaining populations that are free of nonnative iguanas occur on <2 km 2 islets with low estimated population sizes (only Petite Terre >1,000 individuals; Angin 2017;Pounder et al 2020). Beyond the spread of I. iguana (Knapp et al 2020), other threats come from habitat destruction, pets and free-roaming livestock, as well as other anthropogenic causes (e.g., vehicle-caused mortality) (Debrot et al 2013;Knapp et al 2014Knapp et al , 2016van den Burg et al 2018c).…”