WHAT IS eDNA?
As organisms move through their environment, they leave parts of themselves behind. These microscopic cells of skin, hair, leaves, feces, mucous, and more each contain DNA. DNA, or deoxyribonucleic acid, is a molecular building block, with a shared structure but a unique arrangement for every plant and animal alive today.
eDNA, or environmental DNA, describes all the DNA left behind by organisms in their environments. This DNA is often more degraded than DNA sampled directly from organisms. However, advances in DNA collection and sequencing methods over the last ten years have made it even easier to use this fragmented organismal DNA to identify the biodiversity that’s interacted with the environment. By targeting specific repeated molecular sequences within DNA, eDNA analyses can identify organisms down to species, and in some cases even track specific populations and individuals.
With careful sampling, eDNA can be collected from a variety of different places. eDNA is most commonly used to monitor marine environments, because the movements of water mean eDNA is dispersed widely over marine environments and so water samples can help us track a lot of the resident marine organisms. However, eDNA samples have also been collected from soil, snow, and air. Each different kind of sample requires slightly different extraction procedures, but the fundamental principles remain the same. eDNA is an active area of research across the world, but many results indicate that eDNA lasts in environments for up to two weeks, meaning samples can create near real-time pictures of a place’s biodiversity.
When identifying organisms from eDNA data, people often have two different focuses. The first, called eDNA metabarcoding, focuses on using the eDNA to build a picture of all the organisms in an ecosystem. These kinds of analyses can help people create a “fingerprint” of ecosystem health, understand how different habitats support different kinds of animals, and illuminate how organisms interact. The second, single species identification, looks for a particular species of interest or concern in the eDNA. This approach can be a powerful and rapid solution for people monitoring the arrival of invasive species in fragile ecosystems or for groups searching for rare and endangered species.
eDNA means people don’t need to see—or even track—where animals live to figure out if they’re living in a given area. Instead, a full picture of an ecosystem’s biodiversity can be built up—theoretically—with a single, easily collected sample of an area. Across the world, more and more people are leveraging eDNA monitoring techniques to generate the critical information needed to confront the enormous environmental problems threatening global biodiversity today.