title: DNA barcode data accurately assign higher spider taxa.
abstract: The use of unique DNA sequences as a method for taxonomic identification is no longer fundamentally controversial, even though debate continues on the best markers, methods, and technology to use. Although both existing databanks such as GenBank and BOLD, as well as reference taxonomies, are imperfect, in best case scenarios "barcodes" (whether single or multiple, organelle or nuclear, loci) clearly are an increasingly fast and inexpensive method of identification, especially as compared to manual identification of unknowns by increasingly rare expert taxonomists. Because most species on Earth are undescribed, a complete reference database at the species level is impractical in the near term. The question therefore arises whether unidentified species can, using DNA barcodes, be accurately assigned to more inclusive groups such as genera and families-taxonomic ranks of putatively monophyletic groups for which the global inventory is more complete and stable. We used a carefully chosen test library of CO1 sequences from 49 families, 313 genera, and 816 species of spiders to assess the accuracy of genus and family-level assignment. We used BLAST queries of each sequence against the entire library and got the top ten hits. The percent sequence identity was reported from these hits (PIdent, range 75-100%). Accurate assignment of higher taxa (PIdent above which errors totaled less than 5%) occurred for genera at PIdent values >95 and families at PIdent values ≥ 91, suggesting these as heuristic thresholds for accurate generic and familial identifications in spiders. Accuracy of identification increases with numbers of species/genus and genera/family in the library; above five genera per family and fifteen species per genus all higher taxon assignments were correct. We propose that using percent sequence identity between conventional barcode sequences may be a feasible and reasonably accurate method to identify animals to family/genus. However, the quality of the underlying database impacts accuracy of results; many outliers in our dataset could be attributed to taxonomic and/or sequencing errors in BOLD and GenBank. It seems that an accurate and complete reference library of families and genera of life could provide accurate higher level taxonomic identifications cheaply and accessibly, within years rather than decades.
authors.affiliation: National Museum of Natural History, Smithsonian Institution , Washington , D.C. , United States.
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Coddington
authors.affiliation: National Museum of Natural History, Smithsonian Institution, Washington, D.C., United States; Department of Biology, University of Vermont, Burlington, Vermont, United States.
authors.forename: Ingi
authors.initials: I
authors.lastname: Agnarsson
authors.affiliation: EZ Lab, Institute of Biology, Research Centre of the Slovenian Academy of Sciences and Arts , Ljubljana , Slovenia.
authors.forename: Ren-Chung
authors.initials: RC
authors.lastname: Cheng
authors.affiliation: EZ Lab, Institute of Biology, Research Centre of the Slovenian Academy of Sciences and Arts , Ljubljana , Slovenia.
authors.forename: Klemen
authors.initials: K
authors.lastname: Čandek
authors.affiliation: National Museum of Natural History, Smithsonian Institution , Washington , D.C. , United States.
authors.forename: Amy
authors.initials: A
authors.lastname: Driskell
authors.affiliation: Department of Invertebrates, Natural History Museum Bern , Bern , Switzerland.
authors.forename: Holger
authors.initials: H
authors.lastname: Frick
authors.affiliation: EZ Lab, Institute of Biology, Research Centre of the Slovenian Academy of Sciences and Arts , Ljubljana , Slovenia.
authors.forename: Matjaž
authors.initials: M
authors.lastname: Gregorič
authors.affiliation: Department of Biology, Biotechnical Faculty, University of Ljubljana , Ljubljana , Slovenia.
authors.forename: Rok
authors.initials: R
authors.lastname: Kostanjšek
authors.affiliation: Department of Invertebrates, Natural History Museum Bern , Bern , Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Kropf
authors.affiliation: National Museum of Natural History, Smithsonian Institution , Washington , D.C. , United States.
authors.forename: Matthew
authors.initials: M
authors.lastname: Kweskin
authors.affiliation: EZ Lab, Institute of Biology, Research Centre of the Slovenian Academy of Sciences and Arts , Ljubljana , Slovenia.
authors.forename: Tjaša
authors.initials: T
authors.lastname: Lokovšek
authors.affiliation: EZ Lab, Institute of Biology, Research Centre of the Slovenian Academy of Sciences and Arts, Ljubljana, Slovenia; Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Miha
authors.initials: M
authors.lastname: Pipan
authors.affiliation: EZ Lab, Institute of Biology, Research Centre of the Slovenian Academy of Sciences and Arts , Ljubljana , Slovenia.
authors.forename: Nina
authors.initials: N
authors.lastname: Vidergar
authors.affiliation: National Museum of Natural History, Smithsonian Institution, Washington, D.C., United States; EZ Lab, Institute of Biology, Research Centre of the Slovenian Academy of Sciences and Arts, Ljubljana, Slovenia.
authors.forename: Matjaž
authors.initials: M
authors.lastname: Kuntner
keywords: DNA barcoding; Family; Genome; Genus; Global Genome Initiative; Taxonomic impediment