Barcoding in the dark?: A critical view of the sufficiency of zoological DNA barcoding databases and a plea for broader integration of taxonomic knowledge

- COI-representation contrasted to the number of currently recognized species.
- 15.13% Total COI-coverage across the recognized biodiversity on Earth.
- On average, 20.76% of each phylum covered with DNA barcodes.
- Several phyla are severely neglected by barcoding campaigns.
- Taxonomic expertise sorely needed in DNA barcoding.

The functionality of standard zoological DNA barcoding practice (the identification of unknown specimens by comparison of COI sequences) is contingent on working barcode databases with sufficient taxonomic coverage. It has already been established that the main barcoding repositories, NCBI and BOLD, are devoid of data for many animal groups but the specific taxonomic coverage of the repositories across animal biodiversity remains unexplored. Here, I shed light on this mystery by contrasting the number of unique taxon labels in the two databases with the number of currently recognized species for each animal phylum. The numbers reveal an overall paucity of COI sequence data in the repositories (15.13% total coverage across the recognized biodiversity on Earth, and 20.76% average taxonomic coverage for each phylum) and, more importantly, bear witness to the idleness towards numerous phyla, rendering current barcoding efforts either ineffective or inaccurate. The importance of further integrating taxonomic expertise into barcoding practice is briefly discussed and some guidelines, previously mentioned in the barcoding literature, are suggested anew. Finally, the asserted values concerning the taxonomic coverage in barcoding databases for Animalia are contrasted with those of Plantae and Fungi.