Out of South America: multiple origins of non-native apple snails in Asia

Apple snails (Ampullariidae: Pomacea) native to the New World have become agricultural and environmental pests widely in southern and eastern Asia since their introduction in about 1980. Although their impacts have been extensively documented, considerable confusion persists regarding their identities and geographical origins. Efforts to resolve the confusion have suffered from inadequate taxonomic and geographical sampling from both native and introduced ranges. Using phylogenetic and genealogical methods, we analysed 610-655 bp of cytochrome c oxidase subunit I DNA sequences from 783 apple snails from 164 Asian locations and 57 native South American locations. In Asia, we found four species of Pomacea in two clades: (1) Pomacea canaliculata and P. insularum, and (2) P. scalaris and P. diffusa. Parsimony networks and mismatch distributions indicate that the non-native ranges of the two most widespread species, P. canaliculata and P. insularum, probably result from multiple introductions. Molecular analyses are consistent with early accounts; non-native P. canaliculata populations trace back to multiple locations in Argentina and have probably been introduced more than once. In contrast, P. insularum was probably introduced from Brazil and Argentina independently. Multiple introductions may, in part, explain the success and rapid spread of these two species. Unlike P. canaliculata and P. insularum, P. scalaris and P. diffusa were probably introduced through the aquarium trade, derived originally from Argentina and Brazil, respectively. Possible physiological, ecological, and native range differences among these four species highlight the importance of accurate identification in understanding invasion patterns and processes, which is vital in developing and implementing management strategies.