Forensic Genetic Analyses of Melanistic Iguanas Highlight the Need to Monitor the Iguanid Trade

Abstract

Lizards within the Iguana iguana species complex are among the most common reptilian pets, with the widest natural geographic range among iguanids. Deep phylogenetic divergence distinguishes multiple mitochondrial clades, and several taxonomic changes have recently been proposed. These small populations, typically island endemics, are threatened by numerous factors, including the international pet trade. Recent investigations reveal the absence of required CITES permits for lawful export of animals, providing evidence of ongoing illegal trade. Additional monitoring of trade in iguanas can be achieved through the application of forensic molecular techniques. In this study, two captive melanistic iguanas were genotyped for molecular markers for which geographic distributions of alleles have been established. Mitochondrial sequencing indicates that both animals carry a haplotype known to originate from the islands of Saba and Montserrat, populations taxonomically proposed to be Iguana melanoderma. Genotypes at 15 microsatellite loci are equally consistent with this origin, given the results of a principal component analysis. This first forensic genetic assessment within the extensive I. iguana pet trade highlights the presence of illegal activity. The need for additional forensic assessments of pet-trade iguanas is evident, especially given that their value is driven by variety and rarity, which is further intensified by recent taxonomic changes.

An integrative approach to assess non‐native iguana presence on Saba and Montserrat: Are we losing all native Iguana populations in the Lesser Antilles?

“…Eventhough a complete overview is still lacking, scalation and coloration patterns have already been found to be highly variable throughout the I. iguana complex. We assessed the presence of enlarged nasal scales and a melanistic facial patch in both the Saba and Montserrat population, given previous morphological assessments of these populations (Breuil et al, 2020;van den Burg et al, 2022). Among both populations, only three Saba animals had enlarged nasal scales (horn) and were additionally assigned as non-native by microsatellite and sequence data.…”

“…Hybrid and non-native iguanas are believed to be more territorially aggressive and have higher reproductive fitness thanks to larger clutch sizes compared with I. delicatissima (van Wagensveld & van den Burg, 2018). Although data on the clutch size from the Montserrat and Saba populations are practically unavailable (Blankenship, 1990;van den Burg et al, 2022), insular Iguana populations have generally been found to have smaller clutch sizes than continental populations (e.g., Fitch & Henderson, 1977;van Marken Lichtenbelt & Albers, 1993;Bock et al, 2018), even though this is believed to be partially climate dependent (e.g., Novosolov, Raia, & Meiri, 2013). The available data suggest that the Montserrat and Saba populations produce clutch sizes within the lower range recorded for I. iguana, potentially allowing reproductive and genetic swamping when non-native or hybrid iguanas would reproduce within these island populations.…”

“…In order to help distinguish non‐native from native iguanas in invaded populations, we also explored the use of novel composite phenotypic tools in addition to scale and color pattern characters (Breuil, 2013) and molecular data (Stephen et al., 2013; Martin et al., 2015; Vuillaume et al., 2015; van den Burg et al., 2018b, 2021b; Miller et al., 2019; Pounder et al., 2020; Breuil et al., 2022; Mitchell, Welch, & van den Burg, 2022). Size‐dependent comparisons across 16 variables indicated that on Saba, genetically‐assigned non‐native iguanas have larger subtympanic plate scales than native iguanas (Figs 5 and 6).…”

“…On Saba, sampling was done opportunistically during a population assessment (van den Burg et al, 2022), where we also collected the following morphometric measurements: snout-vent length, tail length, upper frontleg length, lower frontleg length, upper hindleg length, lower hindleg length, length of 4th toe, head width, head length, snout length, eye length, mouth length, head depth, tympanum height, tympanum width, subtympanic plate height, subtympanic plate width, mid-body spine length, and the presence or absence of an enlarged nasal scale ('horn') (for methodology see Supplementary material); lateral facial measures were taken from the right side. All variables were measured given the knowledge of their SVL dependence and absence of allometry across the I. iguana species complex; topics that will be addressed in a separate manuscript (van den Burg et al in prep.).…”

“…All measurements were taken by the first author. Although melanism was defined as one of the main characteristics of these populations (Breuil et al, 2020), a subsequent study on the Saba population found that very few animals were completely melanistic (van den Burg et al, 2022). Therefore, knowledge about native body coloration is still in need of further assessment.…”