Exploring the co-evolutionary host-parasite complex as a novel tool for monitoring iguanid invasions

Rapid identification of invasive non-native species aids conservation efforts, particularly in threatened and vulnerable species. However, this can be extremely challenging for morphologically similar non-native and native species, especially for those with cryptic coloration and small home ranges. This holds for non-native green iguanas (NNGI; Iguana iguana), which threaten insular Iguana populations through displacement across the eastern Caribbean. Rapid identification of NNGI is critical to strengthen conservation efforts in native insular Iguana spp. Here we assessed whether ectoparasitic Geckobiella stamii mites of Iguana spp. are host-specific and could aid such efforts through rapid identification and monitoring of NNGI presence. We generated an mtDNA mite-iguana dataset for multiple native populations of Iguana delicatissima and the Iguana iguana complex, including islands with NNGI presence. To assess host specificity between different hosts, we also generated data from other reptiles on St. Eustatius. Phylogenies of native G. stamii COX1 and Iguana ND4 genes showed identical topologies with similar divergence patterns, highlighting their co-evolutionary host-parasite relation. On St. Eustatius, we found high divergences (> 22%) between mites from three different reptile hosts, and low divergence (1.71–5.12%) between mites from non-native (St. Eustatius) and native (India) populations of Hemidatylucs frenatus; indicative of host specificity between species. Subsequently, for islands with NNGI, we found that haplotypes of non-native mites and iguanas originated from the same geographic origin, suggesting these were introduced together. Finally, we found non-native mites on native iguanas (spill-over), native mites on non-native iguanas (spill-back), native and non-native mites sympatrically occurring on one iguanid host, and that non-native mites remain present on native iguanas after removal of NNGI. Hence, ectoparasites provide a novel methodology to assess (previous) non-native iguana presence and their incursion pathways.