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Leeches’ Blood Meals Can Be Used to Track Regional Biodiversity

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A smaller-than-thumbnail-sized leech on a leaf.
Researchers have identified DNA in Haemadipsa leeches from a variety of animals, such as muntjacs, macaque monkeys, and rodents, among others. 
© AMNH/M. Siddall

When it comes to tracking animals in a particular area, including for conservation work, it turns out that humans have a tiny, blood-sipping spy on their side. New research led by Museum scientists confirms that examining DNA found in leeches’ blood meals can be used as a powerful tool to provide information about a forest’s inhabitants.

The study, which was published this month in the journal Systematics and Biodiversity, analyzed close to 750 terrestrial leeches in the genus Haemadipsa collected from forests in Bangladesh, China, and Cambodia. (Watch Museum researchers collect leeches on the 2015 Constantine S. Niarchos expedition to Cambodia, which contributed data to this study, in the video below.)


Tell-Tale Leech Meals

Tell-Tale Leech Meals

In their samples, researchers identified DNA from a wide variety of mammals, including muntjacs, macaque monkeys, wildcats, porcupines, rats, and gaur, or Indian bison. They also found DNA from three types of ground-dwelling birds and one species of bat, marking the first time this method has been used to successfully identify these species.

“Our recent work has demonstrated that we can determine what mammals are in a protected area without hunting, without trapping, without the use of scat or hair samples, and especially without camera traps—all of which are problematic methods for one reason or another,” said Mark Siddall, a curator in the Museum’s Division of Invertebrate Zoology and an author on the study. “Instead, by sequencing the host DNA that remains inside of terrestrial jungle leeches for months after feeding, we can out-perform all other methods of biodiversity monitoring in terms of accuracy, completeness, speed, and cost. We even get the small mammals that most other methods miss.”


A tiny leech clings to the fingertip of a human hand.
Host DNA can be used by researchers to identify what animals leeches are feeding on, even months after a meal.
© AMNH/L. Berniker

Siddall and lead author Michael Tessler, a postdoctoral fellow in the Museum’s Sackler Institute for Comparative Genomics, compared sampling invertebrate-parasite-derived DNA, or iDNA, with camera trapping in another recently published study. They found that pairing camera trapping, with the iDNA method allowed for quicker and more complete survey results. 

“This work is turning out to be an extremely useful tool for conservation purposes, and it’s quick and easy to survey a park in this way as you don’t really need to search for the leeches—they come to you looking for a meal,” said Dr. Tessler. “A snapshot of the vertebrates in an area can be taken with just one day’s worth of sampling; the current standard for surveys, camera traps, takes months or longer.”

In their work, Siddall, Tessler, and colleagues also explored genetic diversity among Haemadipsa leeches, and suspect there are likely many new species to be described.