Thu, 2019-09-26 20:12 -- Anonymous (not verified)
I do not Agree

Global biodiversity has been experiencing rapid past and ongoing declines (1). It spurs a more urgent need to discover Earth’s species in case of their extinction. Currently, scientists have adopted DNA barcoding as a fast and cost-effective approach for new species discovery (“DNA barcodes jump-start search for new species”, E. Pennisi, In Depth News, 7 June 2019, p. 920). Indeed, DNA barcoding can assist in categorizing collections into species-like units and unveiling species potentially new to science (2, 3). However, DNA barcoding’s performance in new species identification is, to a great extent, dependent on complete coverage of known species in the reference library.
At present, DNA barcode data are generally scarce in terms of species coverage in the reference library. It is a far cry from our expectation even for the most studied animal barcode—mitochondrial gene cytochrome c oxidase I (COI)—in the Barcode of Life Database (BOLD). There were 296,474 animal species based on COI sequences from BOLD by July 2019 (4)—i.e., approximately 19% of the total described living animal species on Earth (5, 6). Such low species coverage may become a major bottleneck to identification of new species using DNA barcodes as the starting point. If taxonomic studies are not properly conducted further, there is a great possibility that the new species discovered in this case shall turn out to be synonyms of known species. Ultimately, it may lead to synonymy load in taxonomy (7) but not fill gaps in the catalog of Earth’s species. Thus, it is critical to enhance the completeness of the reference library rather than hasten to identify new species through DNA barcodes.
Specimens from herbaria and museums contain enormous valuable information on Earth’s known species. Especially, many of herbarium specimens have been already identified and labelled authentic species names by taxonomists. If these resources can be adequately utilized, species coverage will dramatically increase for the reference library. Some evidences indicate that successful DNA amplification can be achieved in herbarium specimens, even from a more than 200-year-old specimen in the Linnaean era (8, 9). Moreover, well-covered reference library has been effectively constructed by combining DNA reconstruction and DNA-labelled next generation sequencing (10). Despite being faced with huge challenges, innovation endeavors should be further made to develop molecular technologies for herbarium specimens to obtain their DNA barcode sequences.
Taxonomic studies play an irreplaceable role in associating DNA barcode data with valid species identity, whether in construction of the reference library or ultimate determination of new species based on multiple evidences. Only by integration of taxonomic knowledge and modern DNA-barcode technology can we achieve quick and accurate new species identification. To respond to the ongoing global biodiversity crisis, we advocate that barcoding practitioners and taxonomists specialized on various biological taxa around the world must work together to advance a full-coverage plan of Earth’s existing known species for the reference library as soon as possible.

References and Notes:
1.IPBES, “Summary for policymakers of the global assessment report on biodiversity and ecosystem services of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services ”, M. Carneiro da Cunha, G. Mace, H. Mooney, Eds (Secretariat of IPBES, 2019).
2.D. E. Schindel & S. E. Miller, Nature, 435, 17 (2005).
3.R. A. Collins & R. H. Cruickshank, Mol Ecol Resour 13, 969 (2013).
4.S. Ratnasingham & P. D. N. Hebert, Mol Ecol Notes 7, 355 (2007);
5.Y. Roskov et al., “Catalogue of Life: 2019 Annual Checklist” (2019);
6.Z. Q. Zhang, Zootaxa 3703, 5 (2013).
7.A. Dubois, Biol J Linn Soc 93, 857 (2008).
8. L. Z. Drábková,  in Molecular Plant Taxonomy: Methods and Protocols. P. Besse, Ed. (Humana Press, 2014), ch. 4.
9. K. Andreasen et al., Taxon 58, 959 (2009).
10. C. Xu et al., Mol. Ecol. Resour. 15, 1366 (2015).

No competing Interests: 
The following competing Interests: 
Electronic Publication Date: 
Thursday, September 26, 2019 - 20:07
Workflow State: 
<contrib xmlns="" xmlns:atom="" xmlns:hwp="" xmlns:nlm=""><name><surname>Cao</surname><given-names>Yun</given-names></name><email></email><role>biodiversity researcher</role><aff>Nanjing Institute of Environmental Sciences, Ministry of Ecology and Environment of China</aff></contrib>
<contrib xmlns="" xmlns:atom="" xmlns:hwp="" xmlns:nlm=""><name><surname>Yu</surname><given-names>Dandan</given-names></name><email></email><role>biodiversity researcher</role><aff>Nanjing Institute of Environmental Sciences, Ministry of Ecology and Environment of China</aff></contrib>
Full Title: 

RE: Reference library matters for DNA barcoding

Highwire Comment Response to: 
Check this box if you would like your letter to appear anonymously::