ORIGINAL ARTICLE DNA barcoding of Scandinavian birds reveals divergent lineages in trans-Atlantic species

Abstract Birds are a taxonomically well-described group of animals, yet DNA barcoding, i.e., the molecular char-acterization of species using a standardized genetic marker, has revealed unexpected patterns of genetic divergences among North American birds. We performed a compre-hensive COI (cytochrome c oxidase subunit I) barcode survey of 296 species of Scandinavian birds, and compared genetic divergences among 78 trans-Atlantic species whose breeding ranges include both Scandinavia and North America. Ninety-four percent of the Scandinavian species showed unique barcode clusters; the remaining 6 % had overlapping barcodes with one or more congeneric species, which may reflect incomplete lineage sorting or a single gene pool. Four species showed large intra-specific diver-gences within Scandinavia, despite no apparent morpho-logical differentiation or indications of reproductive isolation. These cases may reflect admixture of previously isolated lineages, and may thus warrant more comprehen-sive phylogeographic analyses. Nineteen (24%) of 78 trans-Atlantic species exhibited divergent genetic clusters which correspond with regional subspecies. Three of these trans-Atlantic divergences were paraphyletic. Our study demonstrates the effectiveness of COI barcodes for iden-tifying Scandinavian birds and highlights taxa for taxo-nomic review. The standardized DNA barcoding approach amplified the power of our regional studies by enabling independently obtained datasets to be merged with the established avian barcode library