THE Mekong river teems with life as it flows to the South China Sea. But the unique species found here are under threat from plans to build hydropower dams along the river. A new environmental monitoring technique may help limit the damage, by quickly counting all the species upstream using only DNA pulled out of the river. That information could be used to influence dam locations at the planning stage.
Traditional surveying methods would take years to identify ecological hotspots that dams should avoid 鈥� time developers don鈥檛 want to waste. 鈥淭here鈥檚 no way you鈥檙e going to sample that [large an area] with the traditional methods,鈥� says at the Kunming Institute of Zoology in China.
Yu hopes to speed up surveying by gathering the fragments of DNA littered throughout the environment and identifying the species they belong to with DNA sequencing. He wants to work with Chinese ecologists to carry out 鈥渆DNA surveys鈥� in the Mekong, building up a picture of where rare and vulnerable species live.
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The idea is based on recent research that suggests every river acts as a conveyor belt for genetic material released from cells shed from the species living there 鈥� what鈥檚 called environmental DNA (eDNA). Identifying species like this 鈥� in much the same way that microbiologists use DNA sequencing to identify bacteria in a sample 鈥� could revolutionise wildlife surveys. This would allow biologists to quickly detect many of the species in an ecosystem.
The technique works well for identifying aquatic species. Last year, a team of European ecologists water from streams and ponds in France and the Netherlands for DNA, then cross-referenced their results with extensive traditional surveys. They looked for fish by eye and caught frogs and salamanders in nets. When they compared the results, they found that eDNA showed as many or more fish species at 89 per cent of the sites they visited.
鈥淲ith the techniques we are using, we obtain all the fish species, including the very rare ones,鈥� says at the Joseph Fourier University in Grenoble, France, who carried out the test.
鈥淭he world is permeated with DNA. Collect it and sequence it and you get a much better view of life鈥�
The eDNA survey worked well for amphibians, too: at every survey site, the team found as many or more amphibian species through eDNA as they did through the traditional survey. That鈥檚 because many well-hidden species are hard to find by eye.
It鈥檚 not just useful for water dwellers: eDNA found in rivers could also give a picture of land-dwelling creatures. A group led by at Cornell University in Ithaca, New York, sequenced the eDNA found in samples from eight sites in the Glatt river system in Switzerland. 鈥� everything from aquatic worms and shellfish to plants and fungi that lived on the land around the Glatt.
Taberlet isn鈥檛 sure that river eDNA sampling is good enough to survey all the land in a river鈥檚 watershed. 鈥淵ou鈥檙e at risk of missing a lot of species,鈥� he says. In addition, Deiner鈥檚 team only identified organisms to the family level, not to species. 鈥淲hat can you do with identification at just the family level for biodiversity research? I think there is some improvement to do,鈥� he says.
The sheer scale of rivers gives them potential as environmental monitoring systems, says at Bangor University in the UK. 鈥淵ou could almost use the rivers as an ecological pulse to try to find out how what we鈥檙e doing on the land is reflected in the biodiversity of the river,鈥� he says.
He also points out that eDNA surveys overcome the problem in using taxonomists to identify all of an ecosystem鈥檚 species: no one鈥檚 knowledge is complete. 鈥淓ven a team of taxonomists can only look at the diversity of a community within the limit of what they鈥檙e able to do,鈥� he says.
Yu says eDNA surveys could make wildlife monitoring cheaper, faster and more available to those with fewer resources. 鈥淭he world is just permeated with DNA,鈥� he says. 鈥淵ou just have to collect it and sequence it in the right way, and then you get a much better view of life.鈥�
This article appeared in print under the headline 鈥淩ivers of DNA鈥�
