• To inventory species, scientists usually roam the territories in order to observe and list them.

  • A team of researchers, including members of the Toulouse laboratory "Evolution and biological diversity", worked on the census of mammals in Guyana thanks to the presence of their DNA in water.

  • This study shows that it is possible to detect the presence of animals that usually pass under radars, but also to make a connection between their presence and human activities.

Usually, to know which animals live in a territory, scientists walk for hours through a radius of 100 km and scrupulously note the track of each mammal or insect crossed during their wanderings. In recent years, a new, more modern method has emerged. Thanks to the presence of their DNA in rivers, species that gravitate in certain areas of the world can also be identified. This has just been demonstrated by a consortium of researchers, including those from the Toulouse Evolution and Biological Diversity laboratory, by studying the waters of the Maroni and Oyapock, the two largest rivers in Guyana.

In a study published in the journal

Molecular ecology resources

, they were able to demonstrate the presence of Amazonian mammals without ever having observed them.

Their initial work focused on fish, whose DNA traces can logically be found in the water, thanks to samples taken at 96 sites in this French region of South America.

That they have spread to other animals, whose DNA is usually taken from the soil.

#Science 🔎 # Monkeys, #tapirs, # giant otters & #jaguars leave their #print in #amazonian # rivers

Works published in @molecology #Resources involving @ Opale82582873, S. Brosse & @JeromeMurienne

Brève @ CNRS➡️ https: // t.co/x6wXanrC13

📗https: //t.co/MrxPt5hnL4 pic.twitter.com/MbC7oHbOfi

- Evolution & Biological Diversity (@EDB_Lab) April 22, 2021

“The idea is to be able to compare classic wildlife detections with our methods and see if they are consistent with the known distribution of animals.

We limited ourselves to the emblematic Amazonian fauna, such as the jaguar, the tapir, the giant otter, the spider monkey or the great anteater, around thirty species in total ”, explains Opale Coutant, doctoral student in the EDB laboratory. .

Where there is man ...

If their method made it possible to confirm what we already knew, it also provided new information on a fauna that the classic inventories do not detect.

“They occur during the day, which means that we see very little nocturnal animals, and as they are done on dry land, we see very little water-dependent species such as the otter for example.

In our case, we noticed that we detected better aquatic, semi-aquatic and nocturnal species.

In particular small possums, nocturnal animals and always in the canopy, we detected them where we did not think they were, ”continues the scientist.

The manatee, very discreet, was spotted thanks to its DNA in the estuaries, and the kinkajou, a small arboreal and nocturnal carnivore, was detected in a much more important way than expected.

This study confirms that humans, and their activities, have a real impact on the presence of certain mammals.

Thus, the presence of the giant otter, the jaguar or even the spider monkey is less observed near the living areas of the Guyanese populations, in particular on the Maroni river, very affected by gold panning.

It is in isolated places that the fauna is richest.

"On the other hand, the capybara, one of the largest rodents in the world, can be found everywhere because it is not hunted by humans for its meat, it is a so-called rather anthropophilic species", notes Opale Coutant who hopes that this method will allow us to learn a little more about the presence of fauna in certain places, without disturbing it.


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