The DNA left by the animal in the air, so that we can find it faster.

Biologists and naturalists around the world launched an ambitious project 20 years ago to promote the establishment of a global inventory of biological species.

As they say, if people don't know that these creatures exist on earth, they can't want to save them.

Even the most optimistic estimates suggest that the scientific community currently knows only 1/4 of all biological species in the world.

With the acceleration of species extinction, this has raised concerns about the protection of the global ecosystem.

In fact, these projects are very slow, mainly because it is extremely difficult to identify and describe species, and in many cases, collecting biological samples for DNA sequencing is not an easy task.

The good news is that there is a new way to catalogue global species: extracting DNA from thin air.

This technology is derived from the environmental DNA (eDNA) technology previously proposed by scientists.

EDNA technology refers to the collection and analysis of DNA in water, soil and other environmental samples, in which these DNA fragments come from the DNA released by organisms in the surrounding environment.

Therefore, environmental DNA extracted from the air of a site can provide genetic information about a large number of species living in the area.

It is notoriously difficult to identify insect species, because traditional DNA sequencing methods often lead to insect death, but eDNA technology may be a good way to obtain DNA information of insect species.

In addition, compared with collecting and sequencing the DNA of a single organism, the analysis of environmental DNA is faster, cheaper and can obtain data of multiple species in the environment at once.

Two studies to test eDNA technology were published in the journal Current Biology.

The two studies chose two excellent research sites-Copenhagen Zoo in Denmark and Hammerton Zoo in the UK.

The researchers are well aware of the species and number of species living in the two zoos, thus helping to assess the accuracy of the eDNA method.

The two research teams use different methods to extract air filters from DNA-- vacuum pumps or blowers.

After extracting enough DNA, both teams identified many species in the zoo by sequencing DNA in the air, even those living indoors or hundreds of meters away from the sampling site.

The researchers also gathered genetic information about species outside the zoo: the British team detected the western European hedgehog (Eurasian hedgehog), which is endangered in the UK, while the Danish team found the DNA of squirrels and cats.

The researchers believe that eDNA technology has revolutionized the way biodiversity is monitored-unlike other technologies, animals do not need to be at sampling sites when scientists collect biological DNA.

Elizabeth Clare (Elizabeth Clare, a molecular ecologist at the University of York in the UK, co-author of the UK study) said: "if you are using a camera trap, then the animal must appear in front of the camera because you cannot capture the animal behind the camera.

If a recording or visual survey is to be used, the animals must also be present at the research site.

But eDNA is more like a footprint, a completely different data type.

At this time, animals do not have to be at the sampling site, and you are more likely to capture some unexpected information. "

At the 2021 annual meeting of the British Ecological Society, scientists from Lund University in Sweden presented their project to extract DNA from the air, which is still in the proof-of-concept stage.

Ecologist Fabian Roger (now at the Federal Institute of Technology in Zurich, Switzerland) and colleagues collected and sequenced DNA in the air at three field sites in southern Sweden and identified 85 insect species (including butterflies, beetles, ants, flies) and 9 non-insect species (such as frogs and birds).

Compared with the results obtained by traditional research methods, some species were omitted, but species that were not detected by other methods were also found.

Rogge said that when he was working on monitoring aquatic ecosystems at Lund University in Sweden, he hoped to find new species, but it was difficult to obtain data on biodiversity.

It is estimated that of the 5.5 million species of insects in the world, scientists have described only 1 million species.

Rogge also expressed concern: "recent research shows that the biomass of insects has decreased by 70%, but we are extremely short of relevant data."

It also prompted him to turn to a new method of extracting environmental DNA from the air.

Previously, scientists mainly studied the DNA of soil and water samples, and scientists found pollination species that once fell on flowers by analyzing the DNA on flower samples.

Kristine Bohmann, an ecologist at the University of Copenhagen in Denmark and a co-author of the study in Denmark, said she had also analyzed DNA obtained from fecal samples.

But compared with previous eDNA technology, the method of monitoring biodiversity by simply testing the air is an exciting development.

Borman also said: "it's time to start extracting DNA from the air."

It is also possible to speed up the progress of environmental protection.

However, there are still several problems with eDNA in the air.

First, we don't know how long genetic material can stay in the air.

Whether the researchers detected the DNA recently or a few months ago? some studies have found complete DNA sequences of organisms that have rotted as far back as 10, 000 years ago in permafrost.

But in other environments, for example, if exposed to solar ultraviolet radiation, DNA may decompose quickly.

Another question has to do with species abundance (the number of species in the community): does a species have a larger DNA signal, which means greater species abundance, or does it just indicate that the species happens to be closer to the sampling site? Clare says this is one of the hottest topics in the field of eDNA research: "to put it simply, unless you can strictly control the experimental conditions, it is impossible to detect DNA in the air."