Analyzing Leech Meals to Track Cambodian Mammals

by AMNH on

From the Field posts

During a recent expedition, a team of Museum researchers experimented with a new method of tracking endangered animals. But first, they had to bare their arms and legs and attract bloodsucking leeches.

Last fall, a trio of scientists led by leech expert Mark Siddall, curator in the Museum’s Division of Invertebrate Zoology trekked through the forests of Cambodia in search of Haemadipsida—a family of jawed, terrestrial jungle leeches that feed on the blood of mammals.

Mark Siddall wades in water to collect leeches.
Scientists like Curator Mark Siddall also serve as bait on leech collecting expeditions. 

While the main purpose of the trip, a 2015 Constantine Niarchos Expedition, was to document leech biodiversity in Southeast Asia, the expedition was designed to sample “bycatch” as well—namely, DNA from the blood of these leeches' mammalian meals, which can be preserved in a leeches’ gut for months. 

Back at the Museum, that DNA was sequenced and fed into a database that identifies biological sequences. Matching these strings of sequenced DNA to existing samples let researchers identify which animals the leeches were feeding on—other than humans, whose status as a leech meal the whole team could attest to. These “IDNA” tests provide conservation biologists with a valuable snapshot of species living in a specific area. 

Two mouse deer among leaves in Cambodian forest.
Cambodian mammals like these mouse deer can be hard to track in the wild. 

Tracking elusive, endangered mammals in their native habitats can be difficult and time-consuming work involving the use of sophisticated technology like radio tagging and camera traps. However in recent years, the IDNA method of sequencing the contents of leeches’ stomachs has provided a faster, less expensive alternative to other methods of mammal-spotting.

“What we're able to do is go in, go to a forest just for a day, collect leeches off the ground, collect them off of ourselves, sequence the DNA from their gut contents, and use that DNA to figure out what mammals are in an area, very efficiently,” said expedition member Michael Tessler, a Ph.D.-degree student at the Museum’s Richard Gilder Graduate School. Data from Tessler’s labwork on the DNA gathered from leech guts will form the basis of his dissertation. 

Two researchers crouch on the ground while collecting leeches in Cambodian forest.
Scientific assistant Lily Berniker and Ph.D.-degree student Michael Tessler collect leeches in Cambodia.

The results of the Niarchos expedition to Cambodia could also help conservation biologists refine the leech-gut IDNA method by setting benchmarks for the number of leech species and number of individual leeches to collect when using the method in a given area.

This 2015 Constantine S. Niarchos Expedition was generously supported by the Stavros Niarchos Foundation.