Taxonomy in barcodes

Over the 250 years of taxonomic science, researchers have discovered some 1.7 million species of living beings. But according to Professor Cláudio Oliveira of the Universidade Estadual Paulista (Unesp) in Botucatu’s Institute of Biosciences, it is estimated that around 87% of all existing species are still completely unknown.

By Fábio de Castro

Agência FAPESP – Over the 250 years of taxonomic science, researchers have discovered some 1.7 million species of living beings. But according to Professor Cláudio Oliveira of the Universidade Estadual Paulista (Unesp) in Botucatu’s Institute of Biosciences, it is estimated that around 87% of all existing species are still completely unknown.  According to Oliveira, Brazil is helping diminish this enormous knowledge gap through DNA barcoding, which has been establishing itself as a global standard for the identification of biological species.

During the 7th Symposium of the BIOTA-FAPESP Program held in July in São Carlos (SP), Oliveira affirmed that using DNA barcoding, the Research Network for the Molecular Identification of Brazilian Biodiversity, also known as BR-BoL, is expected to catalog 120,000 specimens of 24,000 species over four years.

The network, which is coordinated by Oliveira, is funded by the National Council for Scientific and Technological Development (CNPq) and is part of the international Barcode of Life project, started in 2004. Data collected is inserted in the Barcode of Life Data Systems database, or BOLD.

“The goal is to catalog 120,000 specimens in the BOLD database over four years. Our estimate is that this corresponds to some 10% of Brazil’s biodiversity,” said Oliveira.

According to him, some 50,000 species of vertebrates, 800,000 species of insects and 200,000 species of flowering plants are known today. But the number of unknown species is far more impressive. 

“It is estimated that the number of ignored species is ten times greater than those already identified taxonomically. The vertebrates are actually well-known: it is calculated that the rate of unfamiliarity is a mere 7%. But this rate is, for example, 15% for plants, 65% for mollusks, 80% for protozoa, 90% for insects and 99% for bacteria. This is why a simple and effective means of identification like DNA barcoding is fundamental,” he affirmed.

The BOLD database today has over 106,000 species described in over 1.2 million registered barcodes. The process has been fast, as it began only five years ago. But what stands out is reliability: the technique allows scientists to identify species with over 90% accuracy. 

“The BOLD database is so valuable because of the quality of its data. There are two pages of information for each individual, which is not statistical information. If we identify a sequence identical to one already in the database but find that it is a different organism, we can repair the data. That way, growth of the database progressively improves its quality,” said Oliveira.

Historical error corrected

During the event, which was held together with the 7th BIOTA-FAPESP Program Evaluation Meeting and the BIOprospecTA Evaluation Meeting, Oliveira presented a conference on the application of DNA Barcoding in the comparative study of fauna.

He described a study done by his group that, thanks to DNA Barcoding, identified and corrected a historical taxonomic error. In an article published in Zootaxa magazine, the scientists revealed that there were two names for a single species of mullet.

The project “Phylogeography of the mullet species Mugil liza and M. platanus” is funded by FAPESP as Regular Research Awards. 

 “The Mugil liza species was identified in 1836 in Maracaibo, Venezuela. In 1880, the supposed Mugil platanus species was identified in Buenos Aires, Argentina. But with DNA barcoding, the different mullet species showed a genetic distance of nearly 20%. Between liza and platanus there was only 0.2%,” explained the researcher.

Before the study, the mullet found between Venezuela and Cabo Frio (RJ) were considered to be Mugil liza and, from there until Argentina, the Mugil platanus.  Both presented, in fact, some morphological variation. 

“The genetic analysis showed that the differences were a polymorphism brought about by the variation in water temperature. This difference holds no taxonomic validity. It is a single species distributed in the Atlantic Ocean and all of South America. In 2010, we described the species with its true name: Mugil liza,” said Oliveira.

The scientist also coordinates the Thematic Project “Biodiversity and phylogenetic relationships of the genera Astyanax, Hemigrammus, Hyphessobrycon and Moenkhausia”, with FAPESP funding.