– DNA barcodes for all species –    
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hyles_kromaFraction of Hyles chromatogram.







| DNA-barcodes |

    Hyles gallii barcode.

DNA barcodes

Only a small fraction of species found on Earth are described
Almost 10 million species are estimated to exist on Earth, although the real number may be many times greater. Despite a history of efforts to identify species that spans 250 years, the number of species described thus far is fewer than 2 million. In addition, species description has been undertaken in many cases only for the most accessible species. For instance, new species of birds, mammals, trees or butterflies are discovered only rarely today, while taxonomic work on many more challenging groups of species is far from finished. In practice, traditional taxonomic research conducted by specialists and based on morphological features is in crisis, and in many cases, morphology-based species identification is difficult or even impossible. For example, the morphological identification of numerous, ecologically highly important small animals and fungi living in soil is extremely demanding.

DNA-based species identification dates from the 2000s
The idea of species identification based on DNA characteristics was introduced in 2003 (Hebert et al. 2003), taking advantage of the fact that DNA determines the hereditary characteristics of individuals and gives each species a unique DNA composition. Automatic and objective identification can be achieved if a genomic region with a suitable speed of evolution can be found, i.e., with only low sequence variation within a species, but great variation among species. The idea is comparable to the barcodes used in industry, where different items such as grocery products can be identified automatically and unambiguously with a scanner at a store’s checkout counter. Researchers tested the suitability of the cytochrome c oxidase (COI or cox1) region in mitochondrial DNA for this purpose and discovered that it effectively discriminates species from each other. The cytochrome oxidase gene is found in all eukaryotic species because it codes for a protein essential in cell respiration. The suitability of COI for species discrimination has been bolstered by numerous studies later conducted in diverse groups of animals. It is now known that animal species can generally be identified very effectively based on COI (but some closely related species may have identical DNA barcodes), although the same gene segment is not applicable to the identification of fungi and plants. In fungi, the chosen DNA barcode is the nuclear ITS region, and in plants, at least for now, a combination of two chloroplast gene regions (matK and rbcL) is used for DNA barcoding.

It has quickly become apparent that DNA barcodes could be effective also in the discovery and discrimination of so-called cryptic species, those which closely resemble each other but are biologically distinct species. Research has proven that even well-studied groups or geographical regions, e.g., the butterflies of Finland, may include such species. Using DNA barcodes, it has been possible to demonstrate that, for instance, some groups of parasitic wasp species include perhaps dozens of species specialized to different host species and which cannot be distinguished morphologically. The great number of cryptic species has surprised researchers and highlights the view that DNA-based species identification is often the only way to truly distinguish species from each other.

DNA barcoding revolutionizes taxonomical research and species identification
Because a vast amount of taxonomical research and species identification is conducted worldwide, there has been much discussion on the question of DNA barcode-based species discrimination. Some researchers strongly oppose the idea, while others see that the effectiveness of DNA barcodes in distinguishing species as enabling much faster and more reliable identification and discovery of new species than ever before. Despite theoretical disagreements, the fact is that DNA barcodes crucially accelerate taxonomical research. Species descriptions that include DNA barcodes in a pivotal role are being published at an increasing rate. For some species groups, DNA barcodes are the only useful source of information for discriminating species. Thus, DNA barcodes are revolutionizing the entire field of traditional taxonomy.

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