Collecting DNA instead of counting species
A new method simplifies the determination of species diversity: instead of collecting and characterizing species individually, the DNA of organisms is determined from environmental samples. Researchers at UZH and Eawag have now demonstrated for the first time that the method works in rivers.
Most natural ecosystems are strongly affected by changes in human habitat, climate change or invasive species. For ecology and nature conservation, it is of central importance to assess the state of and changes in biodiversity. To protect ecosystems, one must know the organisms living in them. However, classical methods are often only suitable for identifying a subset of organisms. Moreover, they are expensive, and the organisms themselves must be collected for this purpose.
Recently, the idea has been to collect the DNA of organisms from environmental samples such as soil or water instead, and thus detect the different species. All organisms constantly release DNA into the environment, for example through feces or skin particles. This environmental DNA is sequenced using the latest technology and then matched with databases to determine species. "This novel approach has the potential to revolutionize the study of biodiversity," says Florian Altermatt, Professor at the Institute of Evolutionary Biology and Environmental Sciences at the University of Zurich and the Eawag Water Research Institute.
DNA from mayflies and from beavers
He and his team at Eawag in Dübendorf recently provided practical proof of this idea. They collected water from the Glatt, a river in Canton Zurich, at various locations and then extracted all the DNA. "We scooped up a liter of water and were then able to extract DNA from an astonishing number of species, from aquatic insects like mayflies to beavers that live further upstream," study coordinator Altermatt explains. DNA from thousands of organisms was compared to traditional estimates of biodiversity. This clarified whether the organisms detected actually live in this environment.
In earlier work, the authors had already shown that rivers transport DNA several kilometers. "This opens up new approaches to obtaining information about the diversity of organisms in river systems," Altermatt says. "We may now soon be able to determine biodiversity in much the same way that water chemistry is measured." The individual water samples contain information not only about aquatic organisms, but about terrestrial organisms that occur along the river. This gave scientists a fingerprint of organisms living throughout the watershed. And they are proving the potential of environmental DNA to determine the biodiversity of everything from aquatic insects to mammals.
Routinely determine biodiversity
The study by UZH researchers shows that rivers, with their unique network structure, collect and transport environmental DNA that contains information about organisms in the water and on the land. Because the process can be automated, biodiversity data could be collected in the future with unprecedented spatial and temporal resolution. "I could imagine that water samples that are now taken daily or even hourly by cantonal or national authorities for screening chemicals could also be used to record biodiversity," Altermatt speculates.
