A drone as a DNA collector

Flying helper: Scientists have constructed a drone that can land on tree branches and take samples of environmental DNA from there. This genetic material contained in feathers, fur, faeces or animal remains can then reveal which animal species live in the treetops. DNA collection is made possible by adhesive strips on the sides of the drones, to which material from the tree branches sticks.

When it comes to finding new species or uncovering the diversity of past habitats, biologists are increasingly turning to environmental DNA – the remnants of genetic material that find their way into the environment through skin, faeces or carcasses. Even the breath can leave traces of DNA in the air , for example. Environmental DNA can even survive for millions of years in the soil or in the seabed , only recently it provided insight into a unique “ lost world ” in the Arctic.

The problem, however, is that while DNA samples are usually easy to obtain from soil and water, it is difficult to obtain traces of genetic material from a dizzy height, for example from treetop branches. Until now, scientists had to undertake daring tree climbs.

Drone flies independently through the branches

Now there is a remedy – with a flying helper. A research team led by Stefano Mintchev from ETH Zurich and the Swiss Federal Research Institute WSL has developed a drone that can land on tree branches and take samples from there. The quadrocopter navigates independently in dense branches and can even land on springing, flexible branches – a real challenge. “Landing on branches requires complex controls,” explains Mintchev.

This is made possible by a special protective ring that protects the drone’s rotors from collisions with branches – while at the same time providing it with information about its surroundings. The horizontal ring with a diameter of 44 centimeters is combined with four arches running perpendicular to the plane of the ring, which are made of a flexible material and are equipped with sensors. The pressure of the branches on these sensor arcs tells the drone how dense and flexible the branches are.

Adhesive tape as DNA traps

In order to be able to take DNA samples from the surface of the branches and leaves, the drone has several collection surfaces that are adhesive on both sides on its underside. Adhesive strips attached to the outside are also so loose and flexible that they partially enclose the landeast and thus increase the collection area. Biologists can then extract DNA from the adhering material in the laboratory, analyze it and assign it to different organisms using database comparisons.

In a first practical test, Mintchev and his team had the drone collect samples from the crowns of seven tree species – with success: they were able to detect the DNA of 21 different groups of organisms in the adhering material, including birds, mammals and insects. “This is encouraging as it shows that the collection technique works,” says Mintchev.

competition in the rainforest

In the next step, the researchers want to make their DNA drone even faster and more efficient. Her goal is to enter an international robotic species mapping competition in Singapore. The drones and their teams have to capture as many different species as possible in a 100-hectare rainforest area within 24 hours. Not an easy task, because the frequent rain in the tropical forest makes the flight and also the DNA extraction more difficult.

“We are therefore very curious to see whether our collection method will also prove itself under extreme conditions in the tropics,” says Mintchev. In preparation, the researchers are already training in a mini rainforest in the tropical house at Zurich Zoo. “This has the advantage that we know which species occur. This allows us to better assess how fully we are collecting environmental DNA traces with this technique, or if we are missing something,” explains Mintchev. (Science Robotics, 2023; doi:10.1126/scirobotics.add5762 )

Source: ETH Zurich