DNA-kierre

DNA barcoding helps identify living species

The development of gene technology also makes taxonomy – the scientific classification of species – easier. Species can be identified with the help of a short segment of DNA, just like a barcode is used to identify a product in a store. The method improves our perception of species, the number of species, and biodiversity. 

There are an estimated 10 million different species of living organisms, of which we know about two million. Biologists therefore have their hands full in describing and identifying species, even though taxonomy originated already 260 years ago. DNA sequencing is joining identification guides, species collections, loupes, and microscopes as tools used in species identification. A DNA barcode can be found in the genotype or genome of every species.

Species identification through DNA identifiers has been under development for nearly twenty years. Now there is an effective method for animals, plants, and fungi. A DNA barcode library is being created in the international IBOL (International Barcode of Life) project, which aims at ultimately including all living species in the world. 

Finland's contribution to the project, FinBOL (Finnish Barcode of Life), has produced DNA barcodes for about 20,000 species so far.

“The University of Oulu is coordinating DNA barcoding for Finland”, says Senior Curator Marko Mutanen of the Ecology and Genetics Research Unit at the University of Oulu. Mutanen is the coordinator of the FinBOL project which is a part of the national FinBIF research infrastructure project.

“In addition to Oulu, the universities of Helsinki and Turku, and many devotees are also involved.”

Faster, more reliable, and more inclusive

The idea of DNA barcoding was first put forward in 2003. It was noted at the time that the cytochrome c oxidase gene (COI or cox1) of mitochondrial DNA can be used for differentiating animal species from each other. 

Since then, barcode areas have also been sought for fungi and plants. With fungi the ITS region of the nuclear genome is used as the DNA barcode area, and with plants a combination of two genes in the chloroplast is used.

“The sequencing techniques have developed at a dizzying pace in the past decades”, Marko Mutanen says. “Not even the price is a significant impediment anymore.”

What is the use of DNA barcoding in biological research?

“There are many groups of species in which it is nearly impossible distinguish one species from another based on external identifiers alone. In these species a DNA barcode is the only reliable, or at least the most practical, way to identify species. A DNA barcode also works in imperfect, broken samples, and in all phases of the development of the individual organism”, Mutanen explains. 

“The method is fast and objective. It saves the time of experts in the busy identification phase.”

The catch from a single insect trap can be thousands of individuals. Identifying the species of each individual requires massive amounts of human labour – now all the genetic material can be isolated from the catch to determine the species of the individuals with the help of DNA barcodes.

Species follow-ups can be made with new volume and precision. This is of great benefit when we follow the changes by species or in overall biodiversity.”

Snout moth cardinalis 

Uncovering cryptic species 

So-called cryptic species are particularly interesting for researchers. 

“A cryptic species is a species that has previously been mistaken for another species because of similar appearance. A species of moth that we have thought to be a single species of snout moths called Pyralis regalis turned out to be a species pair, which are very difficult to distinguish from each other based on appearance,” Mutanen says. 

Finding cryptic species changes our perception of overall diversity. Naming ecologically important key species also improves our understanding of ecosystems.

“Roundworms are ecologically very important decomposers. They are impossible to distinguish based on appearance to their species, but thanks to the DNA barcode, it works.”

“Cecidomyiidae are another interesting group. We do not know if there are 500 or perhaps 5,000 species of them in Finland”, Mutanen says. “This is being currently studied for an upcoming master's thesis.” 

Vitally important sawflies 

In recent years Marko Mutanen has focused on using DNA barcoding in his studies on sawflies. 

“There are many species of sawflies. They are common and they are especially numerous at northerly latitudes. We have about 800 sawfly species, but in many cases the boundaries between species are unclear and it is difficult to distinguish separate species using traditional methods”, Mutanen explains.

Sawflies are an important source of food for many birds. For instance, they are the main source of nutrition in the first summer in the life of a young black grouse.

“Without sawflies there would be no black grouse”, Mutanen says.

The endangered white-backed woodpecker is also dependent on sawflies, as it survives the winter by eating their larvae. A single tree that a white-backed woodpecker uses in winter has tens of thousands of larvae of Xiphydriid, which are classified as sawflies. White-backed woodpeckers survive the winter with the help of a few winter trees - decaying leafy trees.

Neodiprion sertifer, which is an infamous destroyer of forests, is another type of sawfly. Better knowledge of this ecologically important group of species is possible through DNA barcoding.

“I collected sawflies as museum specimens for several years. I added an extra phase to the process: I removed a leg from each individual sawfly and sequenced the DNA barcode. More than 7,000 tissue samples have now been analysed. Specifying species will become easier when the DNA barcodes allow the establishment of a comprehensive reference library.”

Sawflies Dolerus germanicus



Text: Satu Räsänen
 

Last updated: 1.10.2020