If you sneeze from allergies, you know: animal dander is in the air.
Two research groups have now been able to detect DNA from many kinds of animal are found in the atmosphere. It’s a discovery that could lead to easier and cheaper ways to survey what kind of animals are in an ecosystem.
The ability to detect so many species in air samples using DNA is a significant leap because it means that not only are spores from animals floating around, there’s other DNA material.
For more than a decade, researchers have analyzed those disparate sources of DNA in water to identify elusive organisms.
Researchers’ sampling of environmental DNA (eDNA) in lakes, streams, and coastal waters has let them identify invasive species like lionfish as well as rare organisms such as the great crested newt.
More recently, some scientists have tracked insects by eDNA on leaves, and also found soil eDNA apparently left by mammals loping along a trail.
Far fewer studies have been done on animal eDNA in air. It’s not obvious how much tissue wafts off animals or how long the genetic contents of those cells persist in air.
Earlier this year, Elizabeth Clare, a molecular ecologist now at York University in Toronto reported that eDNA from naked mole rats could be detected in air samples taken in the laboratory.
To find out whether animal eDNA could be detected outdoors, she and colleagues from Queen Mary University of London went to a zoo: There, the species are known and absent from the surrounding landscape, so the team could determine the source of airborne eDNA they found.
In December 2020, Clare set up vacuum pumps with filters in 20 locations in Hamerton Zoo Park and let each run for 30 minutes.
Clare collected 72 air samples from both outside and inside zoo buildings. She used polymerase chain reaction to amplify the scant genetic fragments left on the filters into enough DNA for sequencing.
“We had to take a leap of faith that it was there because it wasn’t something you can measure,” she says in Science Magazine.
After sequencing the eDNA, she matched the snippets to known sequences in a database. The team identified 17 species kept at the zoo and others living near and around it, such as hedgehogs and deer. Some zoo animal DNA was found nearly 300 meters from the animals’ enclosures. She also detected airborne DNA likely from the meat of chicken, pig, cow, and horse fed to captive predators indoors.
All told, the team detected 25 species of mammals and birds.
Meanwhile, researchers in Denmark had pursued the same idea. Kristine Bohmann, a molecular ecologist at the University of Copenhagen, recalls inspiration struck while brainstorming proposals for a high-risk grant program.
“I remember saying, it has to be crazier—like vacuuming DNA from air, that would be insane,” she said in Science Magazine.
They won the grant and sucked up air from three locations in the Copenhagen Zoo with vacuums and fans in three types of samplers. They consistently detected animals—a total of 49 species of vertebrate.
Experts caution that many questions remain about the approach, including the key issue of how far eDNA travels on air, which will influence how well the method can pinpoint the recent location of animals.
That distance will depend on many factors, including the environment; eDNA will probably waft farther in a grassland than in a forest. Another question is how exactly animals shed the DNA. It could be when cells are freed as they scratch or rub their skin, sneeze, or do any vigorous activity like fighting or subduing prey.