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 “You can't conserve a species or population without knowing
where they are. Once we have that foundational information, we
can do the nitty gritty of conservation biology: trying to boost
populations through habitat restoration, reintroductions, or any
number of established conservation tools,” says Ethan Kessler,
doctoral student in the Department of Natural Resources and
Environmental Sciences (NRES) and the Illinois Natural History
Survey at the University of Illinois. Kessler is the lead author
on the study.
Kessler and his collaborators tested how well an emerging
environmental sampling technique known as environmental DNA, or
eDNA, could detect alligator snapping turtles in a southern
Illinois river system. The idea is that all organisms shed DNA
in the environment as they go about their daily business.
Therefore, a simple scoop of soil or water should theoretically
contain trace amounts of DNA from all the organisms recently
inhabiting or passing through a given area.
“We’re finding that eDNA is really sensitive to the presence of
a variety of organisms in both aquatic and terrestrial habitats,
and that expands our ability to find hard-to-detect creatures in
hard-to-sample environments,” says Eric Larson, assistant
professor in NRES and co-author on the study.
The research team knew alligator snapping turtles were in Clear
Creek, a southern Illinois stream feeding into the Mississippi
River, because they put them there. A reintroduction program has
put 400 to 500 young turtles into the system since 2014 and work
is ongoing to determine the introduced population’s viability.
Each turtle is outfitted with a tracking device. To find them,
researchers have to walk or kayak around the site with a
less-than-waterproof radio receiver, set up and check traps, and
interact with potentially dangerous snapping turtles.
“It’s time consuming and a lot of effort. And we're limited by
the number of traps that we can check in a day,” Kessler says.
“With eDNA, we can just show up at a location and pull a quick
water sample. You can cover a wide geographic area relatively
rapidly. That saves money, too, considering the cost of
traveling to these remote locations.”
To prove eDNA is capable of detecting alligator snapping
turtles, the research team first identified genetic markers that
matched all of the subpopulations across the species’ range, but
differed from any other turtle species. After radio-tracking
each turtle, they took water samples near the turtles as well as
in dozens of random sites to determine how eDNA travels in a
riverine setting.
The eDNA method was able to detect alligator
snapping turtles up to a kilometer, or two-thirds of a mile,
downstream. Remarkable, considering less than a gallon of water
was taken from each sampling location.
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“This was a great place to test the performance of
eDNA, because there are only so many alligator snapping turtles in
Clear Creek, and we know where many of them are. That gave us
something like the control of a laboratory experiment, but under
very natural conditions in a real ecosystem,” Larson says.
The study also identified shortcomings of the method. For example,
the researchers found that stretches of the river that were exposed
to more sunlight represented gauntlets of DNA degradation.
“We know ultraviolet light destroys DNA, but we didn’t know how much
the sun would affect our ability to detect alligator snapping
turtles,” Kessler says. “We ended up finding that UV exposure does
have a slight effect on our ability to detect. It’s reducing the
copy number, or the amount of DNA, in our samples.”
Even with reduced copy number in some samples, the researchers were
able to detect the elusive species with fairly high fidelity. The
results suggest eDNA detection could be used as a first step to find
turtles in locations where their status is unknown.
“We developed a tool to rapidly go out and look for this species.
This could be used in regions that historically have records for the
species, but they either haven't been found in many years or have
really low population levels,” Kessler says. “But I think just in
general, as long as you have a species-specific primer, this is a
good tool to use for any rare species. And it's a way to maximize
our time and effort. A lot of animals need help, and conservation
biologists have limited resources and time to try to get the most
good out of the work that we do.”
The article, “Radiotelemetry reveals effects of upstream biomass and
UV exposure on environmental DNA occupancy and detection for a large
freshwater turtle,” is published in Environmental DNA [DOI:
10.1002/edn3.42]. Authors include Ethan J. Kessler, Kurt T. Ash,
Samantha N. Barratt, Eric R. Larson, and Mark A. Davis. The research
was supported by the Nature Conservancy and USDA NIFA. The
Department of Natural Resources and Environmental Sciences is in the
College of Agricultural, Consumer and Environmental Sciences at the
University of Illinois.
[Sources: Ethan Kessler/Eric Larson
News writer: Lauren Quinn] |
