Thanks to the new method, scientists may even be able to detect rare animals that don’t show up very often.

The air in the zoo is full of scents. Think of fish that is used as feed to manure from grazing herbivores. But thanks to a new study, we now know that zoo air contains something else as well; and that is the DNA of the animals that live there. Even by sampling air, researchers can now collect enough DNA to identify the animals in the vicinity. And that could well revolutionize the way we map biodiversity.

Monitor animals

Monitoring biodiversity is not that easy. You can set up camera traps and hope the animal you’re looking for walks by. You can also study footprints or feces. But both require intensive fieldwork. “Most of the existing methods rely on the physical presence of the animal,” researcher Elizabeth Clare told Scientias.nl. “It should run into the camera trap, or make noise near a microphone.” And that while some species do not easily betray their presence. Monitoring animals using existing methods can therefore be a particularly difficult task; certainly when it comes to elusive species, or to animals that live in densely wooded or inaccessible areas.

DNA in the air

However, two independent research groups have now shown that there is yet another method for detecting the presence of animals. Because living organisms appear to leave traces, namely DNA, in the air. By sampling the air and analyzing the DNA found in it, it can then be determined which animal species can be found in the vicinity. So it means that researchers have found an effective way to detect animals that don’t show up so quickly. “In this case, the animal may have already left the area, but still left a trail,” Clare explains. “It no longer needs to be present to be detected.”

eDNA
The new method uses eDNA. In addition to the DNA that is in our cells, there is also something called environmental DNA (or eDNA for short). This is DNA that has escaped an organism and is roaming freely in the living environment of that organism. eDNA can be released in many different ways, for example through old, dead cells that release their contents, although any biological material would actually be a source of eDNA. In recent years, eDNA has already been found in water, snow and soil. In water, in particular, this eDNA is already used to determine which species occur where and the state of certain fish populations. Compared to what is found in rivers and lakes, however, monitoring air is much more difficult. This is because the DNA is diluted in the air. Nevertheless, the newly developed method appears to lead to surprisingly good results.

As mentioned, the findings were made by two independent groups of researchers; one based in Denmark and the other in the UK and Canada. Both research groups wanted to test whether eDNA (see box) can be used in the air to detect land animals. To do this, the researchers collected air samples from two local European zoos: Hamerton Zoo Park in the United Kingdom and København Zoo located in the Danish capital. Each team used a different method to filter eDNA from the air, but both managed to detect the presence of numerous animal species within and outside the boundaries of the two zoos.

Analysis

The results of both studies exceeded expectations. “When we analyzed the collected samples, we found DNA from 25 different animal species, including tigers, lemurs and dingoes,” Clare said. “17 were known zoo species. We were even able to collect eDNA from animals hundreds of meters away from the test site. We also found the DNA of walled animals. The animals were inside, but their DNA escaped.”

Researcher Elizabeth Clare uses sensitive filters attached to vacuum pumps to collect more than 70 air samples. Image: York University

The other research group was also stunned by the results. For example, they found 49 species in just 40 samples, including mammals, birds, amphibians, reptiles and fish. Not only did they find the DNA of okapis and armadillos in the air, they even discovered the DNA of a guppy in the pond of the tropical house. Although that may sound strange, Clare says it’s easy to explain. “DNA can be thrown into the air by the movement of water,” she explains. “There is a lot of exchange between terrestrial and aquatic systems. For example, we already know that we can find DNA from terrestrial animals in local water systems through runoff and material movement.”

Outside the zoo

Many of the detected species were kept in the zoos. But surprisingly, both teams also discovered species from the zoo’s surroundings. Examples include the hedgehog – which is endangered in the UK – and the vole and squirrel found around the København Zoo. “Finding these local animals in both studies is the most exciting,” Clare says. “This is also what we ultimately want to do with the technology; use the method to track species in their native environment. It is therefore very exciting that this has been achieved.”

It works!

According to the researcher, the fact that two research teams can independently demonstrate that airborne eDNA can be used to reveal a range of animal species is a huge plus. It not only increases the power of the work, but also clearly shows the potential of the technique. “The two studies confirm the same thing,” Clare says. “We went out with the same goal, used the same kind of environment in a zoo, but we collected material in a different way. Both approaches were successful. This suggests it may be easier to pluck DNA from thin air than we initially thought.”

Follow-up research

The researchers are continuing their study. “We’ll have to keep working on it,” Clare says. “There are still hundreds of questions about how best to collect and analyze DNA from the air.” In addition, air is a challenging substrate to work with, as air surrounds everything. This means that the risk of contamination is high. “In addition, we don’t yet know exactly how environmental conditions will affect the techniques,” Clare continues. “There are still many questions that we need to work on to make sure this method is useful.”

It means more studies are needed to unlock its full potential. But both research teams believe that filtering DNA from the air is a new and promising way for scientists to study biodiversity, which is currently declining rapidly.