First record on fecundity of an Iguana hybrid and its implications for conservation: evidence for genetic swamping of Iguana delicatissima populations by non-native iguanas
The Lesser Antillean iguana, Iguana delicatissima Laurenti, 1768, is a large herbivorous iguana historically ranging from Anguilla to Martinique (Knapp et al., 2014). Following the International Union for Conservation of Nature (IUCN) Red List of Threatened Species™ criteria, the conservation status of this species was recently changed from Endangered to Critically Endangered due to the severity of threats throughout its native range (van den Burg et al., 2018a). The main threat that I. delicatissima faces, besides those of anthropogenic origin and invasive predators, is widespread occurrence and hybridisation with the invasive and non-native Green iguana, Iguana iguana Linnaeus, 1758 (Knapp et al., 2014; Vuillaume et al., 2015; van den Burg et al., 2018a,b). Green iguanas have become widespread throughout the Caribbean and in the Pacific region (Falcón et al., 2012, 2013), and are known to introduce and transfer pet-trade skin infections to native reptile species (Hellebuyck et al., 2017). Identification between both parential and hybrids is possible through either morphological characteristics and hybrids is possible through either morphological characteristics (Breuil, 2013), or molecular data (Malone et al., 2000, 2017; Stephen et al., 2013; Vuillaume et al., 2015; van den Burg et al., 2018c). Both I. iguana, and Iguana hybrids have caused severe genetic pollution of I. delicatissima populations in areas where they have managed to establish, as is the case on several islands in the Guadeloupe archipelago (Vuillaume et al., 2015), ultimately leading to the loss of genetically pure populations of I. delicatissima. This process, caused by hybridisation and introgression, is defined as genetic swamping (Rhymer and Simberloff, 1996; Todesco et al., 2016). To date, no I. iguana invasion has been mitigated and several island populations no longer have genetically pure I. delicatissima individuals (Knapp et al., 2014; van den Burg et al., 2018a). Most of these invasive iguana populations are already well established and widespread throughout I. delicatissima populations, which makes their removal difficult or even impossible, due to both financial and practical reasons, a common occurrence in invasion biology (Simberloff et al., 2013). Given its continued decline, major research is focused towards I. delicatissima conservation and research (e.g. natural history) of genetically pure populations (Knapp and Perez-Heydrich, 2012; Debrot et al., 2013; Knapp et al., 2016; Judson et al., 2018; van den Burg et al., 2018c), though we propose that understanding the natural history of both hybrid individuals and populations is also important for science and conservation. Firstly, such data will provide an understanding of, the thus far unstudied, establishment and invasion dynamics of I. iguana and their hybrids. Secondly, even though pure I. delicatissima individuals are no longer present on several islands, we lack an understanding of the ecological impacts of these substitute hybrids. So far, to our knowledge no study has addressed natural history characteristics of I. delicatissima x I. iguana hybrids, though Bochaton et al. (2016) made comments on osteological features. Here, we describe the first record on I. delicatissima x I. iguana hybrid fecundity based on a single individual caught on St. Eustatius, in the Dutch Caribbean.