First Insights into the Conservation Genetics of the Endangered Obô Giant Snail Archachatina b icarinata , Endemic to the Islands of São Tomé and Prí

Large terrestrial snails are poor overseas dispersers. Yet the Obô giant land snail ( Archachatina bicarinata ) has been considered endemic to both oceanic islands of São Tomé and Príncipe (Central Africa), raising intriguing questions about its origin and inter-island dispersal. Once abundant, populations on both islands declined rapidly in recent decades. To inform conservation, we provide the first genetic assessment of this Endangered species, investigating its phylogenetic affinities within the Achatininae subfamily, and its genetic diversity and structure across both islands. We explored intra-specific diversity using mitochondrial (COI) and nuclear (ITS2) sequences from 65 A. bicarinata individuals sampled across both islands. To infer phylogenetic affinities, we analyzed 27 additional Achatininae species using newly sampled material and available reference sequences. A. bicarinata formed a distinct, well-supported lineage within the sampled dataset. Within the taxa included, it was recovered as the closest to Archachatina marginata . At the intraspecific level, COI revealed strong asymmetry in genetic diversity between islands: the smaller island, Príncipe, contained 91% (20/22) of the detected haplotypes, São Tomé showed a much lower diversity and shared two haplotypes with Príncipe. No variation was detected at ITS2 among the sampled individuals of A. bicarinata . This first genetic assessment of A. bicarinata identifies Príncipe as the likely origin of the species and the main reservoir of its genetic diversity. Our results suggest a more recent history on São Tomé, where the species may have been introduced. Although phylogenetic inferences are constrained by the dataset, the results offer a foundation for understanding the species’ history and guiding future research. In situ and ex situ conservation efforts are urgent on Príncipe Island, where most genetic diversity persists, but populations on São Tomé may serve as a safeguard, namely for having larger extents of available habitat.