ABSTRACTThe populations of native iguanas in the Caribbean Lesser Antilles are threatened by the wide occur-rence and spread of non-native iguanas. Until recently, competitive hybridization was not believed tothreaten the Saba Green Iguana, a subpopulation ofIguana iguana(Linnaeus, 1758) from the island ofSaba. However, the arrival of non-native iguanas has put the native population at risk, leading to achange in the conservation status of the Saba Green Iguana to Critically Endangered, according toguidelines from the International Union for the Conservation of Nature. Here, we generated the com-plete mitogenome of the Saba Green Iguana using Oxford Nanopore long-read technology. The mito-genome is 16,626 bp long and has 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and acontrol region (1194 bp). Noteworthy, this is only the second published mitogenome for theIguanaiguanaspecies complex, despite the known high intraspecific genetic variation.
Matthijs P. van den Burg
Within the northern Lesser Antilles, the island of Saint Martin, including the Dutch part (St. Maarten, a constituent country of The Netherlands) and the French part (the Collectivity of Saint Martin), is considered the main hub for established non-native reptiles, currently numbering ten species (Table 1) (Dewynter et al. 2022; Thorpe 2022). The islands of Saba and St. Eustatius are special municipalities of The Netherlands and frequently trade with St. Maarten. During the last five years, several new non-native reptile species have been reported on Saba and St. Eustatius, which originate from the non-native populations already present on Saint Martin: the Green Iguana, Iguana iguana (van den Burg et al. 2018, 2022) on St. Eustatius, and the Brahminy Blindsnake, Indotyphlops braminus (van den Burg et al. 2021) and Smooth-scaled Tegulet, Gymnophthalmus underwoodi on Saba (van den Burg et al. 2021). It is believed that these newly established populations have been facilitated by poor biosecurity between the islands. Here, we describe the establishment of two species, G. underwoodi and the Common House Gecko, Hemidactylus frenatus, on St. Eustatius.
Caribbean flora and fauna have always coped with the destructive forces of hurricanes. However, climate change leading to an increase in their frequency and strength, and because many species have declined in abundance due to anthropogenic causes, a better understanding of how hurricanes effect local populations is essential.
The Quill before and after Hurricane Irma. Photo credit: Hannah Madden
2017 Hurricane Season
The 2017 Caribbean hurricane season was the most intense recorded to date. Both Irma and Maria, category-5 hurricanes, closely passed Sint Eustatius and caused major destruction on the island; reported in this Nature Today article. Although immediately after the storms it was clear that trees were heavily affected and mostly defoliated, understanding which species were affected and to what extent requires time for data collection and comparison. Since 2017, several studies have provided pieces of information in order to understand how local populations coped, or not, with the 2017 hurricane season.
Since 2017, researchers found that >90% of all trees were defoliated by more than ¾, and that especially trees at higher elevations (such as on the Quill volcano) were affected more severely. Another study that focused on the Bridled Quail-dove (Geotrygon mystacea), demonstrated that the population declined by 77% in 2019 compared to pre-hurricane levels. A follow-up study in 2021 (not yet published) recorded a further decline to just 125 individuals, and the Bridled Quail-dove will likely be re-assessed by the IUCN.
Focusing on reptile species, a novel study further aids our understanding of the ecosystem-wide impact that the 2017-hurricane season had on Statian biodiversity:
The new study, focusing on the Critically Endangered Lesser Antillean iguana (Iguana delicatissima), shows that its population decreased by at least 20% during 2017. Comparing sighting and survey data from 2017–2018, the authors found a decrease in both the occupancy and population size of the iguana species. Importantly, no recovery was observed in 2019, suggesting that this already small population needs multiple consecutive years without major hurricanes to recover. Interestingly, similar to Statia’s forests, iguanas at higher elevations were found to have been affected more severely.
Letter Antillean Iguana. Photo credit: Philippa King
Small islands such as Sint Eustatius are home to declining populations of rare and endangered species. In many cases, these isolated populations are unable to migrate between islands and thus populations can only increase in size locally. These new studies highlight the need to improve habitat quality and lower anthropogenic threats to optimize the natural recovery of these species. Ideally, at least for population increase could be aided by a local head-starting project where baby iguanas are nourished in temporary captivity and released once they are larger and more likely to survive.
You can find the full study here entitled “Hurricane-induced population decrease in a Critically Endangered long-lived reptile” using the DCBD link below.
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Published in BioNews 54
Invasive alien species are among the main drivers of the ongoing sixth mass extinction wave, especially affecting island populations. Although the Caribbean is well-known for its high species richness and endemism, also for reptiles, equally important is the regional contribution of non-native species to island biodiversity. The Lesser Antilles encompass high genetic diversity in Iguana, though most native populations either have gone extinct or are declining following competitive hybridization with invasive non-native iguanas. Here we assessed non-native presence in two poorly-studied native melanistic Iguana iguana populations using available genetic tools, and explored utilizing size-dependent body measurements to discriminate between native and non-native iguanas. Genetic samples from Saba and Montserrat were genotyped across 17 microsatellite loci with STRUCTURE and multivariate analyses indicating non-native iguanas presence only on Saba. This was corroborated by mtDNA and nDNA sequences, highlighting a non-native origin in Central America and the ABC islands. We identied preliminary evidence suggestive of hybridization. Morphological variation among size-dependent characteristics showed that non-native iguanas have signicantly larger subtympanic plates than native iguanas. Non-native individuals also differed in scalation and coloration patterns. Overall, our ndings demonstrate the need for continuous monitoring for non-native iguanas within remaining native Iguana populations in the Lesser Antilles, with those not directly threatened by non-native iguanas restricted to only 8.7% of the historic range. Although genetic data allows for identication of non-native or hybrid iguana presence, this eld-to-lab workow is time consuming. Rapid in-situ identication of non-native individuals is crucial for conservation management, and besides scale and coloration patterns, we have highlighted the utility of size-dependent variables for rapid diagnosis. We urge regional partners to build morphometric databases for native Iguana populations that will help to quickly detect future incursions of non-native iguanas and allow the rapid implementation of effective countermeasures during the early phase of invasion.
Simple Summary: The illegal pet trade remains an ongoing, substantial threat to wild populations,
especially small insular populations, and can even lead to extinction. Fraudulent activity within the
global reptile trade is known to occur, but its identification through forensic applications depends
on knowledge of diversity within wild populations. In this study, we assessed the geographic origin
of melanistic iguanas (Iguana iguana), which are only found in nations that have never authorized
legal export of live animals. Analysis of genetic data from two pet iguanas in the USA flag these as
originating from Saba or Montserrat, from which no export permits have ever been issued, confirming
their illegal origin. Despite the international trade in I. iguana, in which tens‐ if not hundreds of
thousands of specimens are traded each year, only a handful of individuals have been genetically
assessed. Our work highlights the utility of applying forensic genetic techniques to this trade in
order to track and discourage illegal activity.
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.
Abstract.– Intraspecific diversity is among the most important biological variables, although still poorly understood for most species. Iguana iguana is a Neotropical lizard known from Central and South America, including from numerous Caribbean islands. Despite the presence of native melanistic I. iguana populations in the Lesser Antilles, these have received surprisingly little research attention. Here we assessed population size, distribution, degree of melanism, and additional morphological and natural history characteristics for the melanistic iguanas of Saba, Caribbean Netherlands based on a one-month fieldwork visit. Using Distance sampling from a 38- transect dataset we estimate the population size at 8233 ±2205 iguanas. Iguanas mainly occurred on the southern and eastern sides of the island, between 180-390 m (max altitude 530 m), with highest densities both in residential and certain natural areas. Historically, iguanas were relatively more common at higher altitudes, probably due to more extensive forest clearing for agricultural reasons. No relationship was found between the degree of melanism and elevation, and few animals were completely melanistic. Furthermore, we found that body-ratio data collection through photographs is biased and requires physical measuring instead. Although the population size appears larger than previously surmised, the limited nesting sites and extremely low presence of juvenile and hatchling iguanas (2.4%), is similarly worrying as the situation for I. delicatissima on neighboring St. Eustatius. The island’s feral cat and large goat population are suspected to impact nest site quality, nest success, and hatchling survival. These aspects require urgent future research to guide necessary conservation management.
The native herpetofauna of the Lesser Antillean island of Saba (13 km2; 17.63°N, -63.24°W) includes one snake, Alsophis rufiventris, and four species of lizards, Anolis sabanus, Iguana melanoderma, Sphaerodactylus sabanus, and Thecadatylus rapicauda (Powell et al. 2015). Here, we report the establishment of both Gymnophthalmus underwoo-di Grant, 1958 and Indotyphlops braminus (Daudin, 1803) on the island.
Catastrophic events, like hurricanes, bring lethal conditions that can have population-altering effects. The threatened Caribbean dry forest occurs in a region known for its high-intensity hurricane seasons and high species endemism, highlighting the necessity to better understand hurricane impacts as fragmentation and clearing of natural habitat continues. However, such studies remain rare, and for reptiles are mostly restricted to Anolis. Here we used single-season occupancy modeling to infer the impact of the intense 2017 Atlantic hurricane season on the critically endangered Lesser Antillean Iguana, Iguana delicatissima. We surveyed 30 transects across eight habitats on St. Eustatius during 2017-2019, which resulted in 344 individual surveys and 98 iguana observations. Analyses of abundance and site occupancy indicated both measures for 2018 and 2019 were strongly reduced compared to the pre-hurricane 2017 state. Iguanas at higher elevations were affected more profoundly, likely due to higher wind speeds, tree damage and extensive defoliation. Overall, our results indicate a decrease in population estimates (23.3-26.5%) and abundance (22-23.8%) for 2018 and 2019, and a 75% reduction in the number of opportunistic sightings of tagged iguanas between 2017-2018. As only small and isolated I. delicatissima populations remain, our study further demonstrates their vulnerability to stochastic events. Considering the frequency and intensity of hurricanes are projected to increase, our results stress the urgent need for population-increasing conservation actions in order to secure the long-term survival of I. delicatissima throughout its range.
Species are commonly described as either diurnal or nocturnal, with rare reports of deviations outside their normal activity period. Observations of nocturnal activity by diurnal Anolis are limited to lizards utilizing anthropogenic light sources (night-light niche) to prolong their daily activity period. Here, we report nocturnal activity by Anolis cristatellus facilitated solely by natural moonlight and discuss implications for when this behavior would be recognized as common in the future. The identification of nocturnal activity in Anolis is particularly noteworthy given, in contrast to other taxa, our extensive knowledge of this study system which will allow for future ecological studies to better test hypotheses.
Referenced in BioNews 40 article "Diurnal reptile is found to be active during full moon"
Generally, species are described as being diurnal or nocturnal active, depending on physiological limitations; diurnal species are not able to perceive their world in the absence of sunlight. Rare are observations reported where diurnal species are nocturnally active.
For more information please see: Brisbane, J.L.K., van den Burg, M.P. (2020) No need for artificial light: nocturnal activity by a diurnal reptile under lunar light. Neotropical Biodiversity 6(1):193-196. https://doi.org/10.1080/23766808.2020.1844993
Article published in BioNews 40