What is eDNA and what can it tell us?
Environmental DNA (eDNA) is a new tool that scientists use to survey biodiversity, or the variety of living things, in forests, rivers, and other ecosystems.
A simple diagram of DNA. Image: Forluvoft, Public domain, via Wikimedia Commons
All animals and other organisms leave trace amounts of their genetic material – DNA – wherever they go. There is DNA in poop, in shed skin and fur, and in saliva. These trace amounts of DNA are left all over the environment.
An eDNA analysis involves several steps: Scientists collect samples of soil, water, or air and extract DNA from them. They run the extracted DNA through a sequencer, a device that figures out the order of the chemical building blocks in the DNA. Then the scientists compare the DNA sequences against a reference database to figure out which species the DNA comes from.
What’s cool about eDNA is that scientists can detect and monitor animals without seeing or physically capturing them. It is also a useful tool to find species that are hard to spot in the environment.
Scientists use eDNA to study the biodiversity of the remote Corubal River
When scientist Manuel Lopes-Lima and his team decided to study the biodiversity of the Corubal River of West Africa, eDNA analysis seemed like the best way to do so. Manuel Lopes-Lima used to dive or go snorkeling to study aquatic species, but this is a problem in the Corubal River. “Especially working in tropical rivers in remote areas, it’s sometimes dangerous,” he said. “There’s a lot of parasites which might be vectors of diseases, and also dangerous animals like crocodiles and hippos.”
The Corubal River straddles the West African nations of Guinea and Guinea-Bissau before emptying out in to the Atlantic Ocean. This remote river serves as a source of freshwater for animals living in the Corubal river basin. Previous studies of the Corubal River showed that it is home to several species, including Senegal flapshell turtles, African manatees, Nile crocodiles, and hippos.
“Corubal is one of the last free rivers in Africa,” Maunel Lopes-Lima says. “There’s no major big city along the river and no dams, and that makes this river particularly interesting in terms of conservation needs.”
In a study published in the scientific journal Bioscience, Lopes-Lima and the research team described the methods that they used to filter DNA from water samples collected from the Corubal River in 2022. They sequenced the DNA samples found in the river to identify what species were present in the river and surrounding forest.
Using eDNA, they identified 125 species of aquatic and land vertebrates in the Corubal River. The species identified from the river and forest include critically endangered western chimpanzees and freshwater mussels. The eDNA analysis found 21 other species, mostly fish, that weren’t previously known to exist in Guinea-Bissau.
The scientists are also working to collect specimens and tissue samples from animals encountered along the river to build a DNA reference database for the future. For this purpose, they were accompanied by a team of scientists who collected specimens and tissues from animals, especially from insects, mollusks and smaller mammals. These species have not been well-represented in DNA reference databases.
David Brown adapted this story for Mongabay Kids. It is based on an article by Abishyant Kidangoor, published on Mongabay News:
