852 SYSTEMATIC BIOLOGY VOL.54 Sy!(. Bwl. 54(51:852-859,2005 Copyright © Society of Systomaiic Biiiiog ISSN; lI>M-5l57prinl / 107iWi36X<mline TXlIr 10.10Hl)/l()6.15150.'HK13.MB86 The Promise of DNA Barcoding for Taxonomy PAUL D. N. HEBERT AND T. RYAN GREGORY Department of Integrative Biology, Biodiversit]/ Institute of Ontario, Unwersiiy ofCuelph, GueJph. Ontario. NIG 21VI, Camda: E-mail: [email protected] (P.D.N.H.) DNA barcoding is a novel system (designed to provide directed to DNA barcoding has yielded a rich harvest rapid, accurate, and automatable species identifications of scientific insights. This fact has led new organizations by using short, standardized gene regions as internal to provide the support needed to explore the scalabil- species tags. As a consequence, it will make the Linnaean ity of these results across the animal kingdom. The early taxonomic system more accessible, with benefits to ecol- and positive results from this second wave of investi- ogists, conservationists, and the diversity of agencies gations have now motivated larger research groups to charged with the control of pests, invasive species, and coalesce. In fact, the first alliances with a global reach food safety. More broadly, DNA barcoding allows a day have been assembled to lead the development of bar- to be envisioned when every curious mind, from pro- code sequence libraries for all birds and fishes. Segments fessional biologists to schoolchildren, will have easy ac- of much more species-rich groups, such as plants and cess to the names and biological attributes of any species lepidopterans, are in the earlier stages of this process on the planet. In addition to assigning specimens to {www.barcoding.si.edu). These research groups may. in known species, DNA barcoding will accelerate the pace the longer term, form the nuclear units needed for the of species discovery by allowing taxonomists to rapidly barcode initiative to move into the "big science" do- sort specimens and by highlighting divergent taxa that main where success depends upon the coupling of a may represent new species. By augmenting their capa- clearly enunciated, socially significant research agenda bilities in these ways, DNA barcoding offers taxonomists with strong international research alliances. the opportunity to greatly expand, and eventually com- It is also important to note that the quest for large- plete, a global inventory of life's diversity. scale support for DNA barcoding is not being carried out Despite the potential benefits of DNA barcoding to at the expense of taxonomic funding. Indeed, it is clear both the practitioners and users of taxonomy, it has been that any successful campaign to generate this support controversial in some scientific circles (Wheeler, 2004; will result in a substantial infusion of funding for insti- Will and Rubinoff, 2004; Ebach and Holdredge, 2005; Will tutions and individuals engaged in taxonomic research. et al., 2005). A few have even characterized DNA barcod- Overall, the costs associated with DNA sequencing will ing as being "anti-taxonomy," arguing that its implemen- represent a small component of DNA barcoding efforts; tation will signal the death of a system 250 years in the the majority of funding will be employed for global col- making. We feel that this opposition stems from miscon- lection efforts, for the curation of resultant specimens, ceptions about the DNA barcoding effort. As such, we and for developing online databases containing detailed welcome this opportunity to clarify both the rationale information about them. Moreover, it bears pointing and potential impacts of DNA barcoding. In respond- out that the funding already acquired has come from ing to this set of questions, we emphasize the multiple large foundations and government agencies and pro- positive impacts of this approach for taxonomy and bio- grams with no tradition of supporting taxonomic re- diversity science. search, and that in some cases DNA barcoding proposals have competed directly with medical and comparative QUESTIONS genomics projects rather than any related to taxonomic I. Given two billion US dollars (the amount a research. Viewed from this perspective, any large-scale comprehensive program of DNA barcoding is estimated to DNA barcoding effort will represent a substantial boon, cost i\Nhitfield. 2003}), how ivould you spend this money to both financially and scientifically, to biodiversity and tax- benefit taxonomic and biodiversity research, and what wonki onomic research. It will certainly leave a lasting legacy in be the legacy of these data? the form of a comprehensive, widely accessible system for the identification of species. This question ignores an inescapable reality; there is no prospect of a single $2 billion infusion of support for any biodiversity research program. Such a level of in- 2. Globally, alpha taxonomic research (the discovery and vestment may ultimately be achieved—but, if so, it will description ofneiv species) is in crisis. Is DNA barcoding an reflect a staged and geograpWcally dispersed process of expedient solution to this problem or will it expedite positive funding decisions that will depend heavily on its decline? both scientific progress and societal demand for species- In our view the decline of alpha taxonomy is not a level identifications. The small amount of funding so far consequence of the growing use of molecular methods. 2005 POINTS OF VIEW 853 as has sometimes been suggested (Wheeler, 2004). In fact, resolution in 95% to 97% of cases (Hebert et al., 2004b; we expect DNA barcoding to aid the resurgence of tax- Janzen et al., 2005; Ward et al., 2005). When it fails, onomy. DNA barcoding programs will certainly direct it will narrow the options to a small number of con- new funding into the collection and cataloguing of spec- generic taxa (which, in many cases, could be resolved imens. They will, as well, aid taxonomic investigations fully with additional genetic or other data). This impres- by helping to reveal cryptic species (Hebert et al., 2004a, sive performance reflects two impoitant, and perhaps 2004b), by connecting sexes and life stages (Beskansky unexpected, observations: the rarity of mitochondrial se- et al., 2003), and by clarifying problems of synonymy that quence sharing among species and the dearth of deep now consume much taxonomic effort (Alroy, 2002). The barcode divergences within speciee. Constrained in- novelty and scientific promise of DNA barcoding will traspecific variation in diverse animal groups is a key additionally draw public interest to taxonomic and bio- early finding of the DNA barcode effort; one that merits diversity issues, encouraging young researchers to en- deeper scientific investigation. Certainly, coxl shows far ter the discipline and both academic departments and less variation within species than sonie early critics had biomanagement agencies to hire them. projected would be the case (e.g.. Mallet and WiUmott, We are confident that DNA barcoding will play an in- 2003), and this may reflect the impact of selective sweeps creasingly important role as a taxonomic screening tool related to the coevolution of nuclear and mitochondrial because of its ability to rapidly reveal the genetic dis- genomes. Importantly, for the use of barcodes as species- continuities that ordinarily separate distitict species (e.g., level identifiers, barcode differences appear to accumu- Jarizen et a!., 2005; Smith et al., 2005). Its application in late quickly, making it possible to distinguish all but the this fashion will allow an inversion of standard taxo- youngest of sister species. nomic approaches that operate in an a priori fashion—- seeking the morphological discontinuities that signal reproductive isolation an:iong unsorted assemblages of 4. Many taxonomists already practice DNA barcoding organisms. By contrast, DNA barcoding allows a more informalhf when delimiting and discovering species. Is this efficient a posteriori approach where predefined, genet- zurong, and what data are sufficient to demonstrate that a ically divergent groups are examined for trait variation. series of specimens represents a new species with traditional In this sense, DNA barcoding will dearly be a powerful or barcoding methodi? enabler of alpha taxonomy. We recognize both the general utility of genetic data in taxonomic studies and the strong concordance in taxonomic signals from different genes. However, we 3. Overlapping character variation betiveen and iL>ithi}i emphasize that there is no such thing as "informal species is well documented for many character systems. Why DNA barcoding." A DNA barcode is not just any DNA is this any more or less of a prohletnfor DNA harcoding? sequence—it is a rigorously standardized sequence of a Overlap in the variation of single characters is not minimum length and quality from an agreed-upon gene, problematic for any taxonomic system, be it morpho- deposited in a major sequence database, and attached to logical or molecular, so long as multiple characters are a voucher specimen whose origins ar d current status are employed for taxon diagnosis. One common misunder- recorded. In fact, it has already been established that only standing of DNA barcoding is that it is based on a single those coxl sequences that meet these strict criteria will be character, namely "one DNA sequence." In fact, the 648- designated as DNA barcodes by the Mational Center for bp cytochrome c oxidase subunit 1 {coxl or COI ) gene Biotechnology Information's GenBarik (NCBI, GenBank; region used as the DNA barcode standard for members www.ncbi.nlm.nih.gov/Genbank), the European Molec- of the animal kingdom represents a complex compos- ular Biology Laboratory (EMBL; www.embl.org), and the ite character involving hundreds of independently vary- DNA Data Bank of Japan (DDBJ; www.ddbj.nig.ac.jp). ing components. Some of these component characters There is an important distinction between "describ- are invariant and therefore not all 648 bp are informative ing" and "delimiting" species, but a conflation of the within a given taxonomic assemblage, but most are vari- two has created uneasiness about the use of DNA bar- able.