DNA barcoding and species classification of Japanese birds

Abstract

The Check-list of Japanese Birds, 6th ed (OSJ 2000) retained a conservative tendency toward lumping, with regards species classification, and it has become conspicuously inconsistent with the international tendency towards splitting. This inconsistency has increasingly generated difficulties with integration in international activities or databases. In considering revisions for the forthcoming 7th edition, I reviewed the significance of recent advances in DNA barcoding, especially those focused on the distinctive features of birds in Japan and East Asia, and examined the international trends in species concepts and species delimitations. Then, 1 emphasized the importance of further research on the classification of Japanese avian species. DNA barcoding is a project to identify species based on nucleotide sequences from a short target DNA region (mitochondria] COI region in animals). DNA sequence data, with species name, locality, date, data of voucher specimens, and so on, are registered in the Barcode of Life database. About 40% of bird species worldwide and about 96% of Japanese breeding species have already been registered. Barcoding research in the New World suggest that inter-taxon divergences of 2-2.5% should be recognized as a standard measure of species rank, though some recognizable, closely related species are genetically closer than that limit as a result of recent speciation and/or hybridization. The measure of 2-2.5% divergence has also proven to be applicable to birds on the Korean Peninsula and in Scandinavia. Research in Russia and Mongolia has found that 8.3% of bird species have large intraspecific divergences of over 2%. I analyzed the COI sequences of 230 breeding species in Japan combined with those in other Eastern Palearctic regions, and found that 32 species (14%) include clades with more than 2% divergence within them, while 33 species showed less than 2% divergence from closely related species. As an explanation for the many exceptions among Japanese birds and the extent of peripatric speciation on Japanese islands, it is speculated that Japan experienced few population extinctions during the last ice age as a result of glaciers in the archipelago being poorly developed and essentially only montane. Species classification cannot be based simply on DNA barcode sequences, but barcode surveys are a powerful tool for finding those species in need of further biological investigation. Current species concepts divide broadly into two categories, those founded on integrity (or irreversibility) and those based on diagnosability (or monophyly). The two categories have, until recently, been considered contradictory, but new ideas have been put proposed that attempt to reconcile their differences. The General Metapopulation Lineage Concept and Comprehensive Biological Species Concept have enhanced our essential recognition of species. Nevertheless, when compiling a checklist it is necessary to adopt uniform guidelines when assigning species rank. The British Ornithologists' Union, for example, has proposed realistic guidelines for bird species classification. I want to emphasize the need for comprehensive biological research, including: morphology, ecology, behavioral science and physiology as well as molecular biology and taxonomy, in order to make taxonomic decisions. The Ornithological Society of Japan, which is the responsible organization for Japanese bird classification, should pursue valuable research in this direction to confirm its worth.