Marseilles (AFP)

The water samples came from deep in the Peruvian Amazon, taken by scientists tracking the presence of pink dolphins.

Two weeks later, the environmental DNA, or eDNA, delivered its verdict: the traces of the dolphins were there.

Like those of more than 650 other species, including dozens of mammals: jaguars, fallow deer, anteaters, monkeys, and 25 different species of bats.

"It's quite breathtaking," enthuses Kat Bruce, an ecologist specializing in tropical studies and founder of the start-up NatureMetrics, which had carried out the sequencing of the samples on behalf of the WWF.

This new application of DNA research could, according to its promoters, revolutionize the study of biodiversity.

The International Union for the Conservation of Nature (IUCN), which holds its world congress until Saturday in Marseille, has also launched a project of 15 million dollars (12.6 million euros) for the analysis of 30,000 samples that will be taken from some of the largest river basins in the world, Amazon, Ganges, Mekong or Niger deltas ...

- "Lots of poop" -

While all specialists are sounding the alarm on the ongoing collapse of biodiversity, the promoters of this "eBioAtlas" believe that it will in particular make it possible to shed light on which programs should be given priority in an area with still too limited funding.

+ The IUCN therefore plans to use this data in particular for its emblematic "Red List" of threatened animals.

“We hope that the eBioAtlas will evolvely plug the knowledge holes in this mass extinction,” said Mike Morris, who is leading the project for NatureMetrics.

Listing living things using eDNA John SAEKI AFP

"This technology makes it possible to tell where the different species are found in a simple and fairly precise way," summarizes Paola Geremicca of the IUCN.

Because living species constantly lose cells, leaving genetic traces in their wake.

Hair, skin, mucus, saliva, it all ends up in rivers.

But above all, "there's a lot of poop," says Dr. Bruce.

Droppings from fish or other animals, brought in by the rain, or left behind when bathing or drinking.

Their DNA is then detectable for several days.

- Discreet sharks -

This eDNA search started about ten years ago.

Kat Bruce dived into it during her doctorate, first of all by trying to identify the different species present in "soups" of mixed insects.

Then, over the course of the experiments, it appeared that the technique also worked to locate fingerprints in water analysis.

The Mekong river in Pak Chom, in October 2019 in Thailand Lillian SUWANRUMPHA AFP / Archives

Sequencing of one or two liter samples takes two days and typically yields around 30 million traces of DNA.

There are so many that it is the reference databases that are lacking to identify all the species.

In samples from the Peruvian Amazon, for example, only 20% of traces of fish could thus be formally identified down to the species level.

When the test results are passed on to local experts they are often "stunned" to discover the amount of unknown species, says Morris.

We must then turn to zoos or local institutions in search of a specimen that can make a reference.

Or seek to find one in nature, with simplified collection kits.

In a study published in 2018, researchers found in samples taken in the coastal waters of New Caledonia, French territory in the South Pacific, the DNA of a much larger number of shark species than those identified in 20 years of visual observations.

"Even if the inhabitants do not see sharks when they bathe, they are always there," notes David Mouillot of the University of Montpellier, co-author of this study.

This researcher is participating in another eDNA-based project, Vigilife, a public-private group which aims to develop an "observatory of living things".

One of the limits of the technique today is the plant world, plants being more difficult to identify precisely.

The eBioAtlas will also initially focus on vertebrates, with the ambition of creating an open-source database, free for researchers and NGOs and paid for for companies.

In any case, the technique seems to have a bright future.

Researchers in Britain and Denmark conducted experiments this year filtering air samples in zoo enclosures.

They found there e-DNA traces of resident animals ... but also other species of local fauna.

© 2021 AFP