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These Scientists Survey Rainforest Diversity Using Leeches and the Blood They Suck

DNA from their host animals can persist in adult leeches for at least four months

A leech found in Vietnam (Paul Bertner/Visuals Unlimited/Corbis)
smithsonian.com

For most people, spotting a leech stuck on some body part is not a welcome discovery. But for Thomas Gilbert, a researcher with the Natural History Museum of Denmark, finding a blood-sucking invertebrate attached to an ankle is exactly what he wants. Gilbert and his colleague Mads Bertelsen of the Copenhagen Zoo survey remote jungles for rare creatures by sequencing the DNA found in leech bodies, reports Ed Yong for The Atlantic.

When species around the world are declining rapidly thanks to myriad factors including climate change, scientists have an interest in finding exactly who lives where so they can help understand and maybe conserve the world’s biodiversity. Yet in some regions — remote forests, the chilly arctic — it’s hard to get accurate counts. 

Bertelsen, Gilbert, and their team realized that DNA from goats could survive in leech bodies for at least four months after the vampiric meal. And in many cases, collecting leeches from remote areas is a far easier task than finding elusive animals. All the researchers have to do is offer themselves as bait. Using this unorthodox method, the team has surveyed the Central Annamite region of Vietnam. Yong writes:

From just 25 leeches, the team found DNA from six mammals, including pigs, cows, the small-toothed ferret-badger, and the threatened goat-like serow. They also found DNA from the Annamite striped rabbit, which was discovered in 1999 and had (at the time) never been seen in over 2,000 hours of camera-trap recordings. And they even detected DNA from the Truong Son muntjac, a small deer that was discovered in 1997 and has never been seen in the flesh. “That suggests that these animals aren’t as rare as we think or that the leeches are very good at finding them,” says Gilbert.

Because the researchers need to compare the DNA in leeches to known DNA samples, the analysis is still vulnerable to gaps in genomic databases. See Yong’s story to learn why they may have gotten results for a bearded seal in the Vietnam jungle.

Now the team is working with officials in Vietnam’s Yunnan Province in the hopes that they can find the rare, endangered saola antelope. The work will not only contribute to a better knowledge of the state of the world’s animals, but also elevates leeches from gross parasites to side-kicks in the realm of sciences. Unfortunately, the leeches are sacrificed — in a blender — to contribute. 

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