This new drone can collect environmental DNA from tree branches

Landing on tree branches to collect DNA

The mechanism sounds simple, but the reality is far from it. The drone is equipped with adhesive strips - when it lands on a branch, material from the tree sticks to these strips. Researchers can then extract the eDNA in a lab and catalog it using database comparisons. 

"Landing on branches requires complex control," Stefano Mintchev, Professor of Environmental Robotics at ETH Zurich and WSL, said in a statement. Branches vary in terms of their thickness and elasticity and can bend and rebound when a drone lands on them.

Therefore, the aircraft is programmed to approach a branch by itself and remain stable on it to take samples. This was a significant challenge for the scientists. Also, since a drone cannot fathom the flexibility of a branch, the researchers fitted it with a force-sensing cage that enables the aircraft to measure this factor at the scene.

The aircraft has been tested on seven tree species. The samples revealed DNA from 21 distinct groups of organisms, or taxa, including birds, mammals, and insects. "This is encouraging because it shows that the collection technique works," said Mintchev.

Preparing for a flight in a rainforest

Mintchev and his team are currently prepping the drone for a competition in Singapore in which the aircraft has to detect as many different species as possible across 100 hectares of rainforest in 24 hours.

As a precursor, the team is working at 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 said.

Collecting samples in a natural rainforest comes with a host of problems. Incessant rain washes eDNA off surfaces, and wind and clouds could be an obstacle in drone operation. "We are therefore very curious to see whether our sampling method will also prove itself under extreme conditions in the tropics," added Mintchev. 

Study Abstract:

The protection and restoration of the biosphere are crucial for human resilience and well-being, but the scarcity of data on the status and distribution of biodiversity puts these efforts at risk. DNA released into the environment by organisms, i.e., environmental DNA (eDNA), can be used to monitor biodiversity in a scalable manner if equipped with the appropriate tool. However, the collection of eDNA in terrestrial environments remains a challenge because of the many potential surfaces and sources that need to be surveyed and their limited accessibility. Here, we propose to survey biodiversity by sampling eDNA on the outer branches of tree canopies with an aerial robot. The drone combines a force-sensing cage with a haptic-based control strategy to establish and maintain contact with the upper surface of the branches. Surface eDNA is then collected using an adhesive surface integrated with the cage of the drone. We show that the drone can autonomously land on a variety of branches with stiffnesses between 1 and 103 newton/meter without prior knowledge of their structural stiffness and with robustness to linear and angular misalignments. Validation in the natural environment demonstrates that our method is successful in detecting animal species, including arthropods and vertebrates. Combining robotics with eDNA sampling from a variety of unreachable aboveground substrates can offer a solution for the broad-scale monitoring of biodiversity.