UPSC Prelims 2023 Q69: Aerial Metagenomics and eDNA — Explained
'Aerial metagenomics' best refers to which one of the following situations?
- Collecting DNA samples from air in a habitat at one go
- Understanding the genetic makeup of avian species of a habitat
- Using air-borne devices to collect blood samples from moving animals
- Sending drones to inaccessible areas to collect plant and animal samples from land surfaces and water bodies
Answer: (a) Collecting DNA samples from air in a habitat at one go
Statement-wise explanation
- a: correct — Metagenomics means sequencing the genetic material taken directly from an environmental sample, such as water, soil or air, without first isolating or culturing any one organism. 'Aerial' means the sample is air. Air carries environmental DNA (eDNA) shed by organisms as skin cells, hair, feathers, pollen, spores and microbes. One filtered air sample can therefore show many species of a habitat at the same time. In two studies published in Current Biology on 6 January 2022, air filtered with fans picked up DNA of 49 vertebrate species at Copenhagen Zoo and 25 mammal and bird species at Hamerton Zoo Park in the UK.
- b: incorrect — This statement reads 'aerial' as if it meant 'avian'. Aerial refers to the medium sampled, which is air. It does not refer to birds. Studying the genetic makeup of the bird species in a habitat would be avian genomics or population genetics. Air sampling picks up mammals, birds, reptiles, amphibians, insects, plants and microbes alike, so it is not limited to birds.
- c: incorrect — Taking blood from individual animals is direct, invasive sampling of one organism at a time. Metagenomics is the opposite approach: it is non-invasive and analyses a mixed environmental sample. The animal never has to be found, caught or touched. Using an airborne device to collect samples does not make the method 'aerial metagenomics'. What makes it so is that the air itself is the sample.
- d: incorrect — Drones that collect plant or animal material from land surfaces and water bodies are a remote way of collecting physical samples. The samples here come from land and water, not from air. Drones can carry eDNA samplers, but the defining feature of aerial metagenomics is DNA taken from air. Using a flying platform to collect samples elsewhere does not meet that definition.
How to eliminate
Split the term into its two parts. 'Metagenomics' means the genomics of a whole community recovered from one environmental sample. The prefix 'meta-' signals a collective view across many organisms rather than one organism. 'Aerial' names the medium, which is air. Only one statement combines both ideas: DNA taken from air, covering a whole habitat in a single sample. The phrase 'at one go' matches the community-wide nature of metagenomics. The other three are traps built on wordplay. One swaps 'aerial' for 'avian' (birds). Two swap 'aerial' for 'airborne devices', meaning drones or flying samplers, and they also describe sampling individual organisms (blood, plant or animal tissue) or land and water surfaces, which is not metagenomics of air. If you know only that eDNA is DNA shed into the environment, you can still choose correctly. Fact to remember: aerial metagenomics, or airborne eDNA, means filtering air to detect the species present in a habitat. Studies at Copenhagen Zoo and Hamerton Zoo Park, published in Current Biology in January 2022, proved the method works.
Know more
Environmental DNA (eDNA) is genetic material that organisms shed into their surroundings through skin cells, mucus, faeces, urine, hair, feathers, pollen and spores. Scientists collect a sample of water, soil or air, extract all the DNA in it, sequence it and match the sequences against reference databases. This lets them list the species present without seeing or catching any of them.
Metagenomics sequences all the genetic material in an environmental sample. It began with microbes, most of which cannot be grown in a lab. Metabarcoding is a related, cheaper method. It uses PCR to copy one short 'barcode' gene (for example, COI or 12S) and identifies species from that gene. The 2022 zoo air studies used this PCR-and-sequence route. UPSC's term 'aerial metagenomics' covers the broad idea of reading biodiversity from air.
| Medium | What it captures | Typical use |
|---|---|---|
| Water eDNA | Fish, amphibians, aquatic mammals, invasive species | River and wetland surveys, detecting rare or invasive fish |
| Soil/sediment eDNA | Microbes, invertebrates, plant roots, ancient DNA | Soil health, past ecosystems |
| Air eDNA | Mammals, birds, insects, plants, fungi, microbes | Terrestrial biodiversity monitoring, pollen and pathogen tracking |
Why it matters
- Non-invasive: no trapping, handling or blood sampling.
- One sample covers many taxa at once, including elusive, nocturnal or rare species.
- Can be repeated and scaled: existing air-quality monitoring stations already filter air and could double as biodiversity samplers.
Limits
- It shows presence, not reliable abundance or age structure.
- It depends on complete reference DNA libraries. Gaps produce unidentified sequences.
- DNA can travel or persist, so a detection may not mean the animal is there now.
- Contamination control is critical.
India's DNA reference work, such as the Zoological Survey of India's barcode submissions and the Wildlife Institute of India's sequencing facility, feeds the reference libraries that eDNA methods depend on.
In the news
In January 2022, two independent teams published in Current Biology that air filtered at Copenhagen Zoo (Denmark) and Hamerton Zoo Park (UK) contained enough DNA to identify dozens of animal species. The finding was widely reported as a new non-invasive way to monitor biodiversity. UPSC asked about the term the next year.