Traditionally, the work of the naturalist has been one of hard work and extreme patience, entailing going out into the field, observing or capturing animals and counting them. Techniques have evolved with the use of camera traps and thermal imaging, but, by and large, ecologists have to either be present with the animals, or the animal has to walk in front of a camera. Now, two teams of scientists have developed a ground-breaking method to monitor which terrestrial species are where by plucking their DNA from thin air.
Just as DNA found from a loose hair or an errant cigarette butt may place a criminal at the scene of a crime, animals leave behind strands of DNA as they go about their business. Dubbed ‘environmental DNA’ or ‘eDNA’, these traces had, until very recently, only been analysed from samples of soil and water. Now, a new airborne-eDNA sampling technique has been devised by the two teams, which published their results simultaneously in Current Biology.
Both teams built devices capable of collecting, analysing and identifying the bits of animal DNA in the air around Snatched from the air us. Kristine Bohmann, a professor at the University of Copenhagen, explains the logistical challenges that ecologists face without this kind of forensic tool. ‘Earlier in my career, I went to Madagascar hoping to see lots of lemurs. I rarely saw them. Instead, I mostly just heard them jumping away through the canopy,’ she says. ‘For many species, it can be a lot of work to detect them by direct observation, especially if they are elusive and live in closed or inaccessible habitats.’
Bohmann’s research team tested its new method at the Copenhagen Zoo. Air was first sucked into a fan-like device that draws in genetic material from sources including animal breath, saliva, fur, or faeces. After air filtration, the team extracted the DNA from the filter and sequenced it. ‘We processed the millions of sequences and compared them to a DNA reference database to identify the animal species,’ says Christina Lynggard, a researcher on the team. They managed to identify 49 separate vertebrate species.
Meanwhile, a second team led by Elizabeth Clare from Queen Mary University of London was conducting a similar experiment at Hamerton Zoo Park in Cambridgeshire. Her team detected DNA from 25 species of mammal and bird. Seventeen were from nearby zoo animals, but eight samples were from non-resident species. There was even DNA belonging to the European hedgehog – endangered in the UK, and precisely the sort of animal that conservationists are interested in monitoring.
‘Collecting and sequencing airborne eDNA has the potential to transform the way natural ecosystems are studied and surveyed,’ says Clare. The non-invasive nature of the technique makes it highly attractive for observing vulnerable or endangered species. In the future, it could be used to monitor how species are changing their distributions in response to climate change, or detect the presence of pests and invasive species in sensitive environments.
Work remains to scale-up the technique, improve battery life and make the devices more portable, but the scientists behind the technique have already made history. ‘It’s a perfect replication of a crazy idea,’ says Clare. ‘We basically said, “We think we can pluck DNA from the sky.” Now, it gives the scientific community confidence that what either team has found has been confirmed by a second group. That’s how science is supposed to work.’