Identifying Invaders: The Case ofCeratium furcoides(Gonyaulacales, Dinophyceae) in South America

Ceratium furcoidesis an invasive freshwater dinoflagellate that in the last three decades has expanded its geographic distribution in South America, being recently found in Parana River floodplain (Argentina). Despite growing concern about the presence and impacts of this invader, information regarding genetic diversity in the Southern Hemisphere is missing. This work constitutes the first phylogenetic characterization ofCeratiumpopulations of South America, particularly, from the Parana system. After taxonomic identification asC. furcoidesbased on morphological traits, two sequencing-based approaches were applied using the ribosomal 18S gene: Sanger sequencing to isolated individuals and high-throughput amplicon sequencing (HTS) to environmental DNA. The sequence ofC. furcoidesobtained shared 100% identity to Asian sequences, and formed a highly supported clade in the constructed reference phylogenetic tree. HTS helped to recover low-frequency genetic variants suggesting the presence of different population ofC. furcoides, and to alert potential invasion in its early stages.