Morphometrics aid identification of non-native iguanas to improve conservation of native Saba Green Iguanas, Iguana iguana (Linnaeus, 1758)

Abstract

The Lesser Antilles are part of the Caribbean biodiversity hotspot with relative high levels of diversity, also within the genus Iguana. However, these islands and their native Iguana populations are equally known for presence of invasive alien species, including non-native Green Iguanas. These threaten native iguanid populations through displacement and competitive hybridisation. The most recent island where the presence of non-native iguanas has been identified is Saba, Caribbean Netherlands. To aid rapid identification of non-native iguanas and potential future arrivals, we assessed the presence of morphometric and meristic differences between native Saba Green Iguanas and non-native Green Iguanas from neighbouring St. Martin. The latter is a shipping hub for the northern Lesser Antilles and the main source of non-native iguanas to surrounding islands as iguanas hitch rides in materials shipments. Our results show 13 morphometric size-dependent characters that significantly differ between both populations. Furthermore, we identified that Saba Green Iguanas have larger and fewer femoral pores compared to the non-native iguanas of St. Maarten. To more accurately identify non-native iguanas on Saba, we highlight that in addition to colouration, the relative size of the dorsal spines and the subtympanic plate, as well as the lengths of the head and snout are useful. These characters are often clearly visible and aid rapid in-situ assessments from a distance without the necessity to capture an individual. Given the currently poor biosecurity on Saba, and the upcoming increased volume of materials to be shipped to the island for construction of a new harbour, these additional diagnostic characters should prove useful in combatting the expected surge in incursions of non-native iguanas.