When conventional methods fall short: identification of invasive cryptic Golden Apple Snails (Pomacea canaliculata; P. maculata) using environmental DNA

Abstract

Cryptic invasions are difficult to distinguish and easily overlooked by conventional identification methods, creating false biodiversity information. Molecular markers represent the only reliable method to distinguish cryptic species to date but require individual tissue samples, which is time-inefficient and difficult during low abundance or early colonization. Newly developed Environmental DNA (eDNA) methods may provide a solution. We compared conventional methods (morphological, physicochemical) and molecular methods (DNA and eDNA) to distinguish two putative species of Pomacea, with the aim to develop an early taxon-specific detection method for effective invasive species management. Novel eDNA methods were assessed in semi-natural (mesocosm) and natural waterbodies across Taiwan for species identification. Morphological characters and physicochemical analysis of P. canaliculata and P. maculata shells demonstrated overlapping qualitative and quantitative measures, which were unable to differentiate species. However, DNA-based barcoding (COI gene) differentiated P. canaliculata, and P. maculata and revealed their distribution. Our eDNA analysis demonstrated overall detection rate of P. canaliculata was significantly higher than P. maculata. Importantly, we detected the active presence of P. maculata in Taiwan, although further studies investigation needed to differentiate pure and hybrids individuals. This pioneering eDNA study quickly and effectively detected P. canaliculata and P. maculata, which could revolutionize tracking two immensely invasive and economically destructive species.