The Promise of DNA Barcoding for Taxonomy

Abstract

DNA barcoding is a novel system designed to provide rapid, accurate, and automatable species identifications by using short, standardized gene regions as internal species tags. As a consequence, it will make the Linnaean taxonomic system more accessible, with benefits to ecologists, conservationists, and the diversity of agencies charged with the control of pests, invasive species, and food safety. More broadly, DNA barcoding allows a day to be envisioned when every curious mind, from professional biologists to schoolchildren, will have easy access to the names and biological attributes of any species on the planet. In addition to assigning specimens to known species, DNA barcoding will accelerate the pace of species discovery by allowing taxonomists to rapidly sort specimens and by highlighting divergent taxa that may represent new species. By augmenting their capabilities in these ways, DNA barcoding offers taxonomists the opportunity to greatly expand, and eventually complete, a global inventory of life's diversity. Despite the potential benefits of DNA barcoding to both the practitioners and users of taxonomy, it has been controversial in some scientific circles (Wheeler, 2004; Will and Rubinoff, 2004; Ebach and Holdredge, 2005; Will et al., 2005). A few have even characterized DNA barcoding as being “anti-taxonomy,” arguing that its implementation will signal the death of a system 250 years in the making. We feel that this opposition stems from misconceptions about the DNA barcoding effort. As such, we welcome this opportunity to clarify both the rationale and potential impacts of DNA barcoding. In responding to this set of questions, we emphasize the multiple positive impacts of this approach for taxonomy and biodiversity science. 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 investment may ultimately be achieved—but, if so, it will reflect a staged and geographically dispersed process of positive funding decisions that will depend heavily on both scientific progress and societal demand for species-level identifications. The small amount of funding so far directed to DNA barcoding has yielded a rich harvest of scientific insights. This fact has led new organizations to provide the support needed to explore the scalability of these results across the animal kingdom. The early and positive results from this second wave of investigations have now motivated larger research groups to coalesce. In fact, the first alliances with a global reach have been assembled to lead the development of barcode sequence libraries for all birds and fishes. Segments of much more species-rich groups, such as plants and lepidopterans, are in the earlier stages of this process (www.barcoding.si.edu). These research groups may, in the longer term, form the nuclear units needed for the barcode initiative to move into the “big science” domain where success depends upon the coupling of a clearly enunciated, socially significant research agenda with strong international research alliances. It is also important to note that the quest for large-scale support for DNA barcoding is not being carried out at the expense of taxonomic funding. Indeed, it is clear that any successful campaign to generate this support will result in a substantial infusion of funding for institutions and individuals engaged in taxonomic research. Overall, the costs associated with DNA sequencing will represent a small component of DNA barcoding efforts; the majority of funding will be employed for global collection efforts, for the curation of resultant specimens, and for developing online databases containing detailed information about them. Moreover, it bears pointing out that the funding already acquired has come from large foundations and government agencies and programs with no tradition of supporting taxonomic research, and that in some cases DNA barcoding proposals have competed directly with medical and comparative genomics projects rather than any related to taxonomic research. Viewed from this perspective, any large-scale DNA barcoding effort will represent a substantial boon, both financially and scientifically, to biodiversity and taxonomic research. It will certainly leave a lasting legacy in the form of a comprehensive, widely accessible system for the identification of species. In our view the decline of alpha taxonomy is not a consequence of the growing use of molecular methods, as has sometimes been suggested (Wheeler, 2004). In fact, we expect DNA barcoding to aid the resurgence of taxonomy. DNA barcoding programs will certainly direct new funding into the collection and cataloguing of specimens. They will, as well, aid taxonomic investigations by helping to reveal cryptic species (Hebert et al., 2004a, 2004b), by connecting sexes and life stages (Beskansky et al., 2003), and by clarifying problems of synonymy that now consum