Questionable Species Names for Distinct Species Clusters: An Empirical Test of the BOLD Molecular Identification Engine.

DNA barcoding is an effective method for species identification, but its practical application, as implemented in the Barcode of Life Data System (BOLD), faces numerous challenges. In our work, we conducted an empirical test of this approach using butterflies of the Volga River region in eastern Europe as a model system. We demonstrate that DNA barcoding is a powerful tool for identifying species clusters of the local fauna studied. However, assigning the identified clusters to scientific species names using BOLD was problematic for more than half of the species analyzed. The reasons for these problems are numerous errors in (1) species and even (2) generic identifications of DNA barcodes in the BOLD database (30% and 26% of all problematic cases, respectively), (3) similarity of DNA barcodes in different species (22%), (4) unresolved taxonomic problems associated with the species names that BOLD suggests as identifications (18%), (5) anomalous barcodes (2%), and (6) incompleteness of the BOLD database (2%). Solving problems 1, 2 and 5 requires improving the DNA barcode curation system and minimization of the identification errors in the BOLD database. Problems 3 and 6 can be partly solved by accumulating DNA barcodes, especially barcodes of local faunas, since populations of different species with identical DNA barcodes often have non-overlapping areas. Problem 4 is the most difficult and requires further intensive taxonomic research to solve it.