Wednesday, April 11, 2018

Leeches: Unexpected Helper to Studying Biodiversity

Leeches. The gross, worm-like vampires of the natural world that can swell to 10x their body size have recently been found to be of some great value. Dr. Michael Tessler, currently conducting post-doctoral research at the American Museum of Natural History’s Sackler Institute of Comparative Genomics, has been collecting leeches in China, Bangladesh, and Cambodia to analyze the blood DNA in their digestive system. The interest in analyzing DNA from the digestive system of leeches stems from a criminal case from 2009
Leeches in the lab. Photo Credit: University of Copenhagen

In 2001 in Tasmania, Australia, Peter Alec Cannon and an accomplice broke into a home, tied up and assaulted a 71 year-old woman, and robbed her. There was little evidence at the scene, except for a large, recently fed leech on the floor of the home. Officers an the victim all lacked evidence of leech bites, so the officers collected the leech as evidence to connect to the assailant. DNA was extracted from the leech and entered into a database, where it sat unidentified until Cannon was arrested for a drug charge in 2008. Following the drug charge, Cannon's DNA was cross checked in the database, and finally connected to the DNA from the belly of a leech from 2001. This case was the first in both Australia and world-wide to identify a criminal suspect using DNA collected from a leech. Following this breakthrough case, the first field study to analyze mammal biodiversity using leeches was conducted in 2012. But there was one flaw with this study: only 25 leeches were caught and analyzed in Vietnam. In comes Dr. Tessler.

The ultimate goal is to see if the leech blood analysis is a viable option for large scale biodiversity observations. Current standards for biodiversity analysis are camera traps, fecal and hair collection, and live capture. Live capture ultimately puts stress on the animals, while fecal and hair collection can often be a difficult task. Camera traps are the present gold standard, but are extremely expensive(about $25,000 as reported in the New York Times article) and require long periods of time for collection. If leeches result in a viable method for analyzing biodiversity on a large scale, the cost would be dropped dramatically (costing about $4,000) and bring this method up to the same gold standard as camera trapping by using the DNA to identify individual species. Only time will truly be able to tell is the collected data from leeches in these broad scale forests, compared with camera trap data, lead to further advancements in the study of biodiversity. 

As a future ecologist, any new techniques in observing biodiversity is extremely interesting to me. And the use of organisms such as leeches to identify species in a large area using the blood ingested by the leech is extremely fascinating. However, this does beg the questions of how how the DNA in blood may degrade the longer it is in the leech after ingestion, and further how reliable this method of collection could be in the longterm? I definitely look forward to the results from Dr. Tessler's research and the future of this method.

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