Phylogenetic tree showing the relationships between the reverse transcriptase domains from the CAMERA database, retroviruses, and LTR retrotransposons. The tree was constructed with the NJ method using the SplitsTree4 software . The bootstrap values were calculated over 1,000 iterations and are indicated for two basal nodes. GOS sequences are labeled by a two- letter code indicating their geographic provenance: Caribbean Sea (CA), Eastern Tropical Pacific (ET), Galapagos Islands (GI), Indian Ocean (IO), North American East Coast (NA), Polynesia Archipelagos (PA), Sargasso Sea (SS); followed by a number indicating filter size: 0.1-0.8 (1), 0.22-0.8 (2), 0.8-3.0 (3), 3.0-20.0 (4). These labels appear with blue background. Species abbreviations: P. mt (Pseudonitzschia multistriata); P. m (Pseudonitzschia multiseries); F. c (Fragilariopsis cylindrus); C. r (Chlamydomonas Reinhardtii); O. t (Ostreococcus tauri); A.a (Aureococcus anophagefferens).