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      Identification of Birds through DNA Barcodes

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          Abstract

          Short DNA sequences from a standardized region of the genome provide a DNA barcode for identifying species. Compiling a public library of DNA barcodes linked to named specimens could provide a new master key for identifying species, one whose power will rise with increased taxon coverage and with faster, cheaper sequencing. Recent work suggests that sequence diversity in a 648-bp region of the mitochondrial gene, cytochrome c oxidase I (COI), might serve as a DNA barcode for the identification of animal species. This study tested the effectiveness of a COI barcode in discriminating bird species, one of the largest and best-studied vertebrate groups. We determined COI barcodes for 260 species of North American birds and found that distinguishing species was generally straightforward. All species had a different COI barcode(s), and the differences between closely related species were, on average, 18 times higher than the differences within species. Our results identified four probable new species of North American birds, suggesting that a global survey will lead to the recognition of many additional bird species. The finding of large COI sequence differences between, as compared to small differences within, species confirms the effectiveness of COI barcodes for the identification of bird species. This result plus those from other groups of animals imply that a standard screening threshold of sequence difference (10× average intraspecific difference) could speed the discovery of new animal species. The growing evidence for the effectiveness of DNA barcodes as a basis for species identification supports an international exercise that has recently begun to assemble a comprehensive library of COI sequences linked to named specimens.

          Abstract

          Can a single gene be used to identify all different animal species? An analysis of 255 North American birds shows that cytochrome c oxidase I might have this potential

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          Most cited references101

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          A simple method for estimating evolutionary rates of base substitutions through comparative studies of nucleotide sequences.

          Some simple formulae were obtained which enable us to estimate evolutionary distances in terms of the number of nucleotide substitutions (and, also, the evolutionary rates when the divergence times are known). In comparing a pair of nucleotide sequences, we distinguish two types of differences; if homologous sites are occupied by different nucleotide bases but both are purines or both pyrimidines, the difference is called type I (or "transition" type), while, if one of the two is a purine and the other is a pyrimidine, the difference is called type II (or "transversion" type). Letting P and Q be respectively the fractions of nucleotide sites showing type I and type II differences between two sequences compared, then the evolutionary distance per site is K = -(1/2) ln [(1-2P-Q) square root of 1-2Q]. The evolutionary rate per year is then given by k = K/(2T), where T is the time since the divergence of the two sequences. If only the third codon positions are compared, the synonymous component of the evolutionary base substitutions per site is estimated by K'S = -(1/2) ln (1-2P-Q). Also, formulae for standard errors were obtained. Some examples were worked out using reported globin sequences to show that synonymous substitutions occur at much higher rates than amino acid-altering substitutions in evolution.
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            Biological identifications through DNA barcodes.

            Although much biological research depends upon species diagnoses, taxonomic expertise is collapsing. We are convinced that the sole prospect for a sustainable identification capability lies in the construction of systems that employ DNA sequences as taxon 'barcodes'. We establish that the mitochondrial gene cytochrome c oxidase I (COI) can serve as the core of a global bioidentification system for animals. First, we demonstrate that COI profiles, derived from the low-density sampling of higher taxonomic categories, ordinarily assign newly analysed taxa to the appropriate phylum or order. Second, we demonstrate that species-level assignments can be obtained by creating comprehensive COI profiles. A model COI profile, based upon the analysis of a single individual from each of 200 closely allied species of lepidopterans, was 100% successful in correctly identifying subsequent specimens. When fully developed, a COI identification system will provide a reliable, cost-effective and accessible solution to the current problem of species identification. Its assembly will also generate important new insights into the diversification of life and the rules of molecular evolution.
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              Mitochondrial pseudogenes: evolution's misplaced witnesses.

              Nuclear copies of mitochondrial DNA (mtDNA) have contaminated PCR-based mitochondrial studies of over 64 different animal species. Since the last review of these nuclear mitochondrial pseudogenes (Numts) in animals, Numts have been found in 53 of the species studied. The recent evidence suggests that Numts are not equally abundant in all species, for example they are more common in plants than in animals, and also more numerous in humans than in Drosophila. Methods for avoiding Numts have now been tested, and several recent studies demonstrate the potential utility of Numt DNA sequences in evolutionary studies. As relics of ancient mtDNA, these pseudogenes can be used to infer ancestral states or root mitochondrial phylogenies. Where they are numerous and selectively unconstrained, Numts are ideal for the study of spontaneous mutation in nuclear genomes.
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                Author and article information

                Journal
                PLoS Biol
                pbio
                PLoS Biology
                Public Library of Science (San Francisco, USA )
                1544-9173
                1545-7885
                October 2004
                28 September 2004
                : 2
                : 10
                : e312
                Affiliations
                [1] 1Department of Zoology, University of Guelph Guelph, OntarioCanada
                [2] 2Program for the Human Environment, Rockefeller University New York, New YorkUnited States of America
                [3] 3National Wildlife Research Centre, Canadian Wildlife Service Ottawa, OntarioCanada
                Article
                10.1371/journal.pbio.0020312
                518999
                15455034
                b4e377fc-1789-4363-b3be-61b4f25a7e36
                Copyright: © 2004 Hebert et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited
                History
                : 13 February 2004
                : 20 July 2004
                Categories
                Research Article
                Ecology
                Evolution
                Genetics/Genomics/Gene Therapy
                Zoology
                Birds

                Life sciences
                Life sciences

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