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Most of us aren’t super
thrilled to bump into a leech,
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given that they are blood-sucking parasites who
are not picky about who they snack on.
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Interestingly, though, that lack
of pickiness means any given leech
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may contain blood from a wide variety of species.
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And that makes leeches an
unexpected ally for scientists
00:00:16
trying to track endangered wildlife.
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And the best part is, you don’t have
to look very hard to find leeches.
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If you’ve got blood in your
body, they will happily find you!
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So let’s get into exactly what makes these
bitey little blood-libraries just so helpful.
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[♪ INTRO]
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A key part of protecting endangered
animals is understanding which species
00:00:37
live where and how their home
ranges might be changing.
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To track wildlife distribution,
scientists can set up traps,
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put out cameras, and collect hair and poop.
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But these methods can be
difficult and time-consuming,
00:00:49
especially for the rarest species in
hard-to-reach places like dense jungles.
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One handy alternative is the use
of environmental DNA or eDNA,
00:00:59
genetic material left behind by
animals in their environment.
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This DNA can be sampled from soil or water and
identified using a technique called barcoding,
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which means looking for short snippets of
DNA that are unique to certain species.
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And soil and water aren’t the only
sources of those genetic leftovers.
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We can also collect DNA
from the bellies of leeches!
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Lots of leeches get their nutrition
by sucking blood from other animals.
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The digestion is pretty slow, so that
blood can linger in their tummies for months,
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and a DNA test can identify what
species they recently fed upon.
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This technique was pioneered in
a 2012 study, which sampled DNA
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from 25 terrestrial leeches collected
from tropical forests in Vietnam.
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The researchers found DNA from
six different mammal species,
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some of which hadn’t been
recorded from that area before.
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This included Annamite striped rabbits,
which hadn’t been observed in the region
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even after more than 2000
nights of camera footage!
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That study showed that leeches can be a
great source of DNA for hard-to-find animals.
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This technique has come to be called
invertebrate-derived DNA, or iDNA.
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On top of all that, leeches
are really easy to collect.
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Researchers simply wander through
the forest and before long,
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their clothes are covered in
leeches looking for a meal.
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It’s as convenient as it is creepy!
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And we do mean on the clothes, by the way.
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Leeches found on the
scientists are generally excluded
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due to the contamination from Homo sapiens.
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Since that 2012 study, more research
has expanded this technique,
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with even more promising results.
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A 2018 study collected over 700 leeches
across southeast Asia and identified the DNA
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of dozens of species of birds and
mammals of various sizes and habits.
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That study found that the leeches
are an especially good source of DNA
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for small mammals like rodents and shrews,
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which can be extra hard to find
using other survey methods.
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One leech in that study even had bat
DNA in its stomach, which was news
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to the researchers, who didn’t know that
these particular leeches ever fed on bats.
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How exactly it got hold of a bat… we do not know.
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All of this is great news for scientists
hoping to help endangered species.
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This leech-derived DNA can
help researchers identify
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which animals live where, including rare species!
00:03:15
And that data then helps
us understand which regions
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are most important in order to
focus our conservation efforts.
00:03:22
This SciShow video is supported by
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00:03:26
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00:03:30
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00:03:32
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00:03:35
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00:03:37
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00:03:42
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00:03:45
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00:03:48
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00:03:55
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00:04:04
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And, you’ll get your first 30 days free!
00:04:11
Already, scientists are putting
this novel technique into action.
00:04:14
A 2022 study gathered DNA from over 30,000
leeches in a nature reserve in China.
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They had more than 150 park rangers help them out
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by collecting leeches during
their regular patrols of the park.
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And once again, all they had to do was pick the
leeches off of the ground or off of their clothes!
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From those samples, not only did
researchers identify DNA from threatened
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and endangered species, but
they were also able to track
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the spatial distribution of
the species across the park.
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They found that native species were
most common in the interior of the park,
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and less common around the edges in areas with
high human activity and lots of livestock.
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Another study in Borneo found a similar
pattern, where leech-derived DNA
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revealed lower wildlife
diversity in parts of the forest
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that had been disturbed by
logging or other human activities.
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Which means these leeches are
actually helping scientists
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to track how our activities
are affecting wildlife.
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And there is even more potential to be tapped.
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For example, not all leeches
are terrestrial blood-suckers.
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One study in 2022 sampled a variety
of parasitic and predatory leeches
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and found gut DNA from fish, insects,
worms, and even other leeches!
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Some researchers have also
pointed out that leeches
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might even contain DNA from
diseases in the blood of their prey.
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This could help us track the spread of diseases
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which can threaten endangered species,
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or ones that could potentially
spread from wildlife to us humans.
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Now, with all that said, leech-derived
DNA is not a perfect tool.
00:05:45
For one thing, even the least picky
leeches don’t feed on literally everything.
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There might be animals that
the leeches don’t like to eat
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or don’t regularly encounter – like the
bat I mentioned, cause you know, like...the wings.
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Those animals are likely to end up
mostly missing from these leech surveys.
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Also we don’t have a perfect understanding
of how far a leech might travel
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after eating, which can make it tricky to
track wildlife distribution with precision.
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Also, some leeches are
protected species themselves!
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Certain types of medicinal leeches
are classified as species of concern,
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so it’s best to avoid bothering
them for these studies.
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That means not all leeches can be
used for this kind of research.
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So, leech-DNA is not a perfect fix to
all of our wildlife-sampling woes.
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But it is absolutely something we
can use side-by-side with methods
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like cameras and other
sources of environmental DNA.
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And leeches aren’t the only source
of invertebrate-derived DNA.
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Other studies have had similar luck
sampling DNA from other bugs that eat blood,
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dung, or carrion, including flies,
beetles, ticks, and mosquitoes.
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The world just full of little critters happily
collecting genetic samples from their neighbors!
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Protecting wildlife is hard work,
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and we need as much information
as we can get to do it right.
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But it turns out there are loads of animals
out there with tummies full of data.
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In the future, we might owe
our conservation successes
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to the parasitic blood-suckers of our world.
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[♪ OUTRO]
