Rare bird\u2019s detection highlights promise of \u2018environmental DNA\u2019<\/p>\n
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Scientists have long pulled DNA from water and soil<\/a>, but they have only just started to see the air as a source of genetic information. Over the past decade or so, researchers have been learning how to measure airborne DNA, study its abundance and use it to put together a picture of an ecosystem\u2019s inhabitants and health<\/a>. Airborne DNA is being used to monitor individual species<\/a>, and being trialled as a way to detect invasive species or attacks with biological weapons. It is also being tested as a way to judge the success of conservation efforts.<\/p>\n The technique promises to link \u201cthe whole [of] biodiversity, the whole world together with a single assay that\u2019s really rapid and that can even be done in the field and analysed in the cloud\u201d, says David Duffy, a researcher who specializes in wildlife disease genomics at the University of Florida in St Augustine.<\/p>\n But there is still a lot to pin down, such as how fast DNA decays in the air and how far it travels. Some genetic material pulled from the air comes from humans, and several scientists are concerned that when using the technique for conservation research, it could inadvertently reveal people\u2019s ethnicity or whether a person has a genetic disorder \u2014 and even be used to identify individuals.<\/p>\n Scratch your head and you\u2019ll release DNA-rich cellular material into the air. There, it will mingle with DNA from myriad other sources: your own and others\u2019 exhalations and exfoliations, fragments of hair, feathers, excrement, pollen and spores, and microorganisms such as viruses and microalgae. This DNA, which can include segments that are tens of thousands of base pairs long, will then wander the air for perhaps a few days, often clinging to dust particles. It can travel distances that range from a few metres to several thousand.<\/p>\n Although eDNA is already collected routinely from water<\/a>, snow and soil, to gather information about biodiversity or to track contaminants or viruses, scientists have not typically monitored sources of DNA in air other than pollen and spores \u2014 robust packages designed to travel on the breeze.<\/p>\n But, in the early 2010s, various ecologists began to wonder whether air might contain useful DNA traces beyond those wrapped in such windborne bundles. In 2013, biologists Matt Clark at the Natural History Museum in London and Richard Leggett at the Earlham Institute in Norwich, UK, took air samples in a greenhouse and outside it.<\/p>\n \u201cWe were just wondering whether we would get anything,\u201d says Clark. \u201cActually, we got dozens \u2014 hundreds \u2014 of things turning up.\u201d<\/p>\n Meanwhile, at Texas Tech University in Lubbock, ecologist Matthew Barnes analysed air samples using techniques developed for collecting waterborne eDNA, and discovered they were teeming with DNA from leaves and flowers, as well as types of pollen not designed to be windborne. He realized then the potential for understanding whole plant communities using air1<\/a><\/sup>.<\/p>\n But it was the discovery of tiger DNA near Cambridge, UK, that alerted the wider community to airborne DNA\u2019s potential. Elizabeth Clare at York University in Toronto, Canada, and Joanne Littlefair at University College London wanted to know whether they could find animal DNA in the air. They collected samples at a small zoo in Cambridgeshire, UK, reasoning that they would know the origin of any DNA they found, because the exotic animals were confined to the park.<\/p>\n In the laboratory, the researchers extracted the DNA from the samples, and amplified and sequenced it. They found that they could sniff out tigers 200 metres away from their enclosure, as well as many of the zoo\u2019s other animals, their food \u2014 including chicken, horse and pig \u2014 and wildlife such as hedgehogs, bats and squirrels. In total, the samples contained DNA from 25 species of mammal and bird, including 17 kept at the zoo2<\/a><\/sup>. Another study near Copenhagen Zoo, published at the same time, had similar findings3<\/a><\/sup>.<\/p>\n \u201cAirborne animal DNA has always been there, it\u2019s just that we\u2019ve never looked for it,\u201d says Simon Creer, who studies molecular ecology at Bangor University, UK.<\/p>\n Technicians collect fungal spores from the air in central Finland.<\/span>Credit:Tommi Sassi, University of Jyv\u00e4skyl\u00e4<\/span><\/p>\n<\/figcaption><\/picture><\/figure>\n But it was a physicist who found a way to scale the method up. James Allerton, at the National Physical Laboratory in London, suggested that Clare examine samples taken by the UK Heavy Metals monitoring network, which has 25 air pumps, located in cities, in the countryside and at industrial sites.<\/p>\n The researchers studied samples from 15 of the network\u2019s sites and, last year, published4<\/a><\/sup> what they say is the world\u2019s first national survey of terrestrial biodiversity using airborne eDNA. They found common UK animals, as well as exotic pets such as parrots and an invasive fish species, the silver carp (Hypophthalmichthys molitrix<\/i>), that had not previously been reported in the region. From vertebrates to single-celled protists, they picked up 1,100 taxa.<\/p>\n To check the reliability of their method, the researchers compared their results with data from massive databases such as iNaturalist, in which citizen scientists record what they see. iNaturalist had failed to pick up half of what the team found. In turn, eDNA did not reflect 43% of the iNaturalist observations. Citizen science tended to find more birds and other charismatic, visible species near human habitation. Airborne DNA picked up more of the small, the invisible and the nocturnal, including fungi, lichens, invertebrates and plants other than trees, says Littlefair. \u201cThese are really the powerhouses of ecosystem function.\u201d<\/p>\n The method, says the team, is \u201ca realistic solution to monitoring the dynamics of life on land\u201d. Now, the researchers are helping countries with similar monitoring networks to do the same.<\/p>\n But what if you could harness a network that pumps huge amounts of air through its filters, and that has records stretching back decades? In 2015, molecular biologist Per Stenberg at Ume\u00e5 University in Sweden heard about just such a possibility \u2014 a 70-year history of biodiversity, told in wisps of DNA caught on tens of thousands of filters and stored at the Swedish Defence Research Agency in Stockholm.<\/p>\n He was at a seminar about Sweden\u2019s radionuclide-detection network, built in the late 1950s to detect nuclear-weapons tests. The 25 stations suck in hundreds of cubic metres of air per hour and the contents are then stored on glass-fibre filters.<\/p>\n Stenberg set about analysing the filters from a station north of the Arctic Circle. Whereas Littlefair\u2019s team searched for short marker regions of DNA that identify individual species \u2014 known as DNA metabarcoding \u2014 Stenberg used shotgun sequencing, in which DNA is broken down into tiny pieces, sequenced and matched to known reference genomes using a computer. The shotgun approach consumes more time and energy and requires more-complex statistical techniques than does the metabarcoding technique. But the results are more detailed.<\/p>\n It was four years before he and his collaborator Mats Forsman, the agency\u2019s research director, got results5<\/a><\/sup>.<\/p>\n \u201cViruses, bacteria, fungi, plants, animals, birds, fish \u2026 the intestinal parasites of moose,\u201d recounts Stenberg. \u201cI mean, whatever was out there and had a reference to match it, we could see \u2014 every single organism that is not extremely rare in the ecosystem.\u201d<\/p>\n The results indicated that the technique could be trusted, he says. \u201cSo then it was like: wow. This is something we need to explore.\u201d<\/p>\nClouds of DNA<\/h2>\n
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Archives of air<\/h2>\n
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<\/p>\n![\"Air](\"https:\/\/media.nature.com\/lw767\/magazine-assets\/d41586-026-01099-2\/d41586-026-01099-2_52266080.jpg?as=webp)