Invasive South African populations of the freshwater snail Tarebia granifera belong to a single globally distributed lineage within a species complex

The Asian thiarid snail Tarebia granifera is a highly successful invasive species and has had substantial impacts in South African freshwater ecosystems, often out competing and replacing native snail populations. However, there is limited understanding of the molecular diversity of the snail beyond its native Southeast Asian range, with few attempts to identify origins or potential number of invasion events in to new freshwater environments. Similarly, identifying T. granifera via morphological methods is complex and a method by which several efforts to monitor the spread of the snail and the parasites they transmit have depended upon. By employing mitochondrial cytochrome c oxidase subunit I DNA barcoding, phylogenetic and species delimitation analyses it has been possible to identify the occurrence of three putative species within T. granifera. However, crucially, the phylogenetic and population genetic analyses revealed only a single lineage to contain all invasive haplotypes of T. granifera including those from South Africa. Also, the population genetic analyses revealed a single haplotype in the South African populations, suggesting a rapid expansion event into several aquatic ecosystems across the country. The current findings are consistent with a single invasion event; however, the current study highlights the inability of single marker techniques to reveal the fine-scale evolutionary history of invasion for T. granifera. Developing genomic tools is crucial to monitor the spread of snail species across southern Africa, to assess their ecological impact and for trematode disease surveillance.