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Special drone collects eDNA from tree branches

Researchers from ETH Zurich and the Swiss Federal Research Institute WSL and SPYGEN have jointly developed a flying device that can land on tree branches to take DNA samples. The development opens up new opportunities for biodiversity researchers.

Ecologists are increasingly using traces of genetic material left by living organisms in the environment, called ecological DNA (eDNA), to catalog and monitor biodiversity. Based on these footprints, researchers can determine which species live in a particular area.

It is easy to obtain samples from water or soil, but other habitats, such as the forest canopy, are difficult for researchers to access. As a result, many species are not tracked in understudied areas.

The developed drone is equipped with adhesive strips. When it lands on a branch, the material from the branch sticks to those strips. Researchers can then extract the DNA in the lab, analyze it, and assign it to the genetic matches of different organisms using database benchmarking.

But not all branches are the same, they vary in thickness and elasticity. The aircraft's software works so that it can autonomously approach a branch and remain stable on it long enough to take samples.

“Landing on branches requires complex control,” explains Stefano Minchev, professor at ETH Zurich and WSL. “Initially, the drone does not know how flexible the branch is, so the researchers equipped it with a force sensor. This allows the drone to measure this factor on the spot and turn it on your flight maneuver.

The researchers tested their new device on seven types of trees. In the samples, they found DNA from 21 separate groups of organisms, including birds, mammals and insects. "This is reassuring as it shows that the collection method is working," says Minchev.

The researchers now want to improve their drone to prepare it for a competition that aims to spot as many different species as possible across 100 hectares of rainforest in Singapore in 24 hours.

To test the drone's performance in conditions similar to those it will operate in the competition, Minchev and his team are currently working at the Zurich Zoo in the Masoala rainforest. "Here we have an advantage - we know what species are present, which will help us better assess how carefully we collect all traces of eDNA with this technique or miss something," says Minchev.

However, for this event, the collection device must become more efficient and faster. In a test in Switzerland, the drone collected material from seven trees in three days, but in Singapore it will need to be able to sample many more trees in one day.

Collecting samples in a natural rainforest, however, poses an even greater challenge for researchers, as frequent rains wash eDNA off surfaces. "Therefore, we are very interested to see if our sampling method can prove itself in the extreme conditions of the tropics," says Minchev.

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