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All
three species of vampire bat live in Central to South
America,
the common vampire bat (Desmodus rotundus),
the
hairy-legged vampire bat (Diphylla
ecaudata), and
the
white-winged vampire bat (Diaemus youngi).
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It’s the nose of the common vampire bat (Desmodus rotundus). These bats belong to
the family Phyllostomidae, one of
three families of leaf-nosed bats (Rhinolophidae and Megadermatidae being the other two families). One of the
exceptional skills mediated by this nose makes use of the same receptor that makes our
mouths burn when we eat chili peppers. Vampire bats can detect the hot blood in
your veins from far away!
It’s the noseleaves of the vampire bat that are so amazing, but maybe we should include the rest of the bat head as well. The ears, teeth,
mouth, and eyes all work with the nose to give this bat some jet fighter
skills.
Leaf nosed bats come in some very odd varieties. The picture
on the below and right will give you some idea of the shapes and sizes possible. The
question is – what’s the reason for these bizarre growths and why isn’t one odd
shape enough? The answer will best be found if we know what their function is,
because in biology – form follows function (except for proteins, see this post).
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Here
are some different leaf nosed bats. Top middle is the Ridley’s leaf
nose
bat; bottom left is the Honduran white bat. Top right is the
Commerson’s
leaf nose bat and the middle bottom is the greater
spear-nosed
bat. The bottom right image is of the cleaf nosed bat of
Vietnam,
a more newly discovered variety. It was first described in
2008,
but it took 4 years to determine if it was a new species or just
a
variant of another species.
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Two basic needs of the bat are to find food and find its
way. Whether it's a fruit bat, an insectivorous bat, or a vampire bat, a bat must be able to negotiate obstacles within its environment and find a
source of nutrition.
To accomplish these tasks, especially given that most bats
are nocturnal, they use
echolocation. They send out a high-pitched sound, and it bounces off objects
and returns to their ears. This is very much like the radar used in airplanes.
But this isn’t all they use. Bats can see just about as well as humans; the phrase
“blind as a bat” might as well be “blind as a Bob.”
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We
said most bats are nocturnal. This is
Livingstone’s fruit bat
or Comoro
flying fox. It is a fruit eating bat of the Comoros
Islands
in the western Indian Ocean (just northwest of Madagascar)
and
is at least partially diurnal. Other bats may be seen during
the
day, but it almost always because they have been disturbed
in
their hiding place or they were disturbed in their
feeding
the night before.
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Different shapes help to increase the difference in the
reflectivity of objects in the area of focus as opposed to those in the
periphery. This allows the various species to hone in what they need to discern
and dismiss those things that are uninteresting. Different backgrounds and
different needs require different nose leaf shapes.
This answers the question about the wild shapes of noses,
but it brings up another question. If vampire bats find their food by
echolocation, sight, and smell, then why do they have heat sensors?
To answer this new question, consider the sizes of the
vampire bat and its intended prey. The bat weighs about 2.5 oz (71 g), but it
needs blood for food (mammalian blood for common vampire bats, bird blood for
hairy legged and white-winged species). In fact, vampire bats are the only mammals that
completely depend on hematophagy (blood
meals). Because of this, they often feed on animals that are over 1000x their
size.
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Pigs
are a favorite source of blood for vampire bats. Here, a
sleeping
pig has been bitten on the snout. Why the snout – read
on.
Notice the bat can hold its weight with its wings, and that
there
seems to be more blood than you would expect from
such
a small bite. Again, read on to know why.
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The bats need to locate a place on the sleeping animals
where blood vessels are near the surface. This is where the heat sensing comes
into play. Vessels close to the surface will give off the most heat to the
environment, and vampire bats can “see” these vessels from up to 20 cm away!
The vessels in question need to be covered with less hair,
so the bat almost always goes for the lower leg or snout. They will land on the
ground, and walk or run up to the prey from behind the animal to make the bite.
Vampire bats wings are much stronger than most other bats, so they have an
easier time moving along the ground, supporting some of their weight on their
wings.
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On
the left you can see the incisors of the vampire bat. The cheek
teeth
and canines are used to shave off any hair from the site, but
the
incisors do the cutting. The lack enamel, so they are always
razor
sharp. On the right, the tongue is being used to take in the
blood.
The tongue is deeply grooved, so the anticoagulant saliva
runs
down into the wound and more blood can easily be lapped up.
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Instinct tells the vampire that a good feeding once will probably mean a good feeding again – if they can find the same animal. So how do they find the same animal several night is a row? They hear them.
A 2006 study showed that vampire bats do tend to feed on the
same individual (be it human or cow) for several nights in a row. They can distinguish
their previous victim by the sounds of their breathing! Every animal has a
unique breathing pattern and sound profile, and the vampire bat can distinguish
between individuals to find the one that matched a previous good meal. Imagine
if we could find our favorite meal again by listening for the clinking of the
right pans!
Returning to a good feeding spot each night, the vampire bat
searches for a surface vessel to drink about 1-2 teaspoons of blood (4-5 ml).
This isn’t enough to harm the animals, and is what allows them to go back
several nights in a row.
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Rabies
can be spread by bats, and they don’t have to bite you.
When
a bat bites an infected animal, it takes in the virus. The
virus
grows in the animal and gets distributed to the saliva as
well.
Startled bats sometimes spit, and if this gets into your
eyes,
mouth, nose, or an open wound, you could contract the
infection.
It’s rare overall, but rabies kills about 60,000
people
a year.
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How do vampire bats locate that ankle vessel they need to
feed on? Back we go to that amazing nose. The heat sensors of bats are called pit organs, just like in the pit vipers we talked about last week. There are three to four of these organs in the noseleaves
of the bat, and a couple across the upper lip as well.
As opposed to the pit vipers, vampire bats have adapted a
heat sensor, not a cold sensor to use as their infrared detector for blood
vessels. TRPV1, the same receptor that is used for the capsaicin burn and heat regulation in mammals, is present in very high numbers in the neurons of the
pit organs.
But this is no ordinary TRPV1. Mammals can’t detect heat
from 20 cm away with a regular TRPV1 – this is a modified TRPV1. A 2011 study found that this version of
the protein is missing the last three amino acids on the carboxy terminus (the
end produced last). This small change increases the sensitivity of the receptor
from 43˚C all the way down to 30˚C, so that small differences in heat can be
noted from almost a foot away.
One more amazing fact - the bats have regular TRPV1 too. The
two version of the protein come from the same gene and the normal one is used
throughout the bat’s body for all the things we use TRPV1 for: heat regulation,
reproduction, cancer inhibition, etc. Only in the neurons of the pit organs is
the mRNA altered after it is transcribed from the gene (alternately spliced) to make the slightly shorter, more sensitive
protein.
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Here
is a cartoon of how blood clots. On the bottom flow chart,
the
first anti-co line is where desmolaris and draculin work.
The
third line is where desmoteplase acts.
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Their mouths have specialized salivary glands that make anticoagulants so no clot is formed. There
is one anticoagulant that someone with a sense of humor named draculin. It acts to prevent blood clot
formation. We have mentioned a second anticoagulant before, called desmoteplase. One of our Halloween posts talked about how it may be good for people that have had strokes. It
dissolves any clots that may form.
A 2014 clinical trial is showing that desmoteplase is better than the tissue plasminogen activator clot busters now being used
(rtPA), since they have a half-life of four hours (as opposed to 5 minutes for
rtPA) and it’s breakdown products aren’t as toxic to nerves and the blood brain
barrier as compared to rtPA.
A newer anticoagulant is called desmolaris. A 2013 study showed that it works on yet another part
of the clotting system to prevent clot formation. And this isn’t all of them. A
2014 protein survey suggests that there may be dozens more anticoagulant
proteins in vampire bat saliva.
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| Which flying machine is more complex and cool? |
Lets add up the vampire bat’s technologies and compare them
to an F16. The bat can fly and turn better. The bat has radar and infrared heat detection. It has high
powered listening devices that can discriminate between two individuals.
Finally, it has biological weapons that allow it to do its work without
alarming the target.
All that in a “machine” that can fit into the palm of your
hand. Defense aeronautical engineers must feel so embarrassed.
Next week, let’s take it just a bit further. Female
mosquitoes aren’t just looking for you, they’re tasting and feeling for you.
They use CO2 gradients as well as my prodigious heat to find me on a warm
picnicking evening.
For
more information or classroom activities, see:
Leaf-nosed
bats –
Echolocation
–
Alternate
splicing –
Anticoagulants
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