A team developed a drone especially to collect DNA samples from hard-to-reach places, such as the top of trees, according to a study published in Science Robotics.
Ecologists need genetic samples of material that organisms leave behind in the environment. This is called environmental DNA (eDNA) and is used to catalogue biodiversity. Researchers can use these DNA traces to identify what species live in a certain area.
Getting samples from water and soil is easy, but reaching the canopy of trees can be challenging. As a consequence, these areas remain poorly explored. To overcome this difficulty, a team from the ETH Zurich and Swiss Federal Institute for Forest, Snow, and Landscape Research WSL and the company SPYGEN have come together to create a drone that can collect samples from inaccessible areas such as tree branches.
The drone has adhesive strips that stick to the tree branches to collect DNA samples. After retrieving the drone, researchers can extract DNA in the lab, analyse it and compare it with various databases to identify organisms present.
However, not all branches are the same. They vary greatly in terms of elasticity and thickness. In addition, branches also tend to bend when the drone touches them. Programming the drone so that it could remain stable long enough to collect samples autonomously was a major challenge for the team.
“Landing on branches requires complex control,” explained Stefano Mintchev, Professor of Environmental Robotics at ETH Zurich and WSL. Before landing, the drone “doesn’t know” how flexible the branch is, so the researchers added a sensor, allowing the drone to measure this elasticity and readjust flight accordingly.
Once the drone was complete, the team tested it on seven different tree species. The results look promising, and the team detected DNA from 21 distinct groups of organisms, including birds, mammals, and insects. “This is encouraging because it shows that the collection technique works,” said Mintchev, who co-authored the study.
The team now wants to enter their drone in a competition to detect as many different species as possible across 100 hectares of forest in Singapore in 24 hours. To prepare the drone, Mintchev and colleagues are working with Zoo Zurich’s Masoala Rainforest. “Here we have the advantage of knowing which species are present, which will help us to better assess how thorough we are in capturing all eDNA traces with this technique or if we’re missing something,” Mintchev says.
For the competition, the drones need to be as effective as possible to collect the samples. In preliminary tests, the drone managed to collect samples from seven trees in three days, but in the competition, it will need to do ten times more trees every day.
This is not going to be easy. Rain washes eDNA off surfaces, and wind and clouds complicate drone operation. “We are therefore very curious to see whether our sampling method will also prove itself under extreme conditions in the tropics,” Mintchev says.
Aucone E, Kirchgeorg S, Valentini A et al (2023) Drone-assisted collection of environmental DNA from tree branches for biodiversity monitoring. SCIENCE ROBOTICS, 8 (74), https://doi.org/10.1126/scirobotics.add5762