belut listrik membuat
melompat untuk serangan
Penelitian menegaskan
cerita 200 tahun lalu oleh Alexander von Humboldt
Date:
June 6, 2016
Source:
Vanderbilt University
Summary:
Seorang ahli biologi menemukan bahwa belut listrik dapat membuat melompat serangan yang secara dramatis meningkatkan kekuatan kejutan listrik mereka, dengan demikian, telah mengkonfirmasi pengamatan berusia 200 tahun lalu oleh penjelajah abad ke-19 yang terkenal dan naturalis Alexander von Humboldt.
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legendaris abad explorer 19 terkenal dan naturalis Alexander von Humboldt menceritakan pertempuran dramatis antara kuda dan belut listrik yang ia saksikan di lapangan perjalanan ke Amazon. Dalam 200 tahun berikutnya, namun, tidak ada laporan ilmiah tentang perilaku serupa pada bagian dari belut, menunjukkan bahwa mungkin cerita von Humboldt dibesar-besarkan.
Tahun lalu, Vanderbilt University biologi Kenneth Catania menemukan bahwa, dalam kondisi tertentu, belut listrik akan bereaksi bahkan lebih dramatis daripada von Humboldt jelaskan: Ketika terpojok oleh benda mengancam yang sebagian terendam, mereka akan sering menyerang dengan keluar dari air, menekan dagu mereka melawan sisi objek dan mengelola serangkaian kejutan listrik yang kuat.
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Electric eels make leaping attacks
Research confirms 200-year-old story by Alexander von Humboldt
Date:
June 6, 2016
Source:
Vanderbilt University
Summary:
A biologist has
accidentally discovered that electric eels can make leaping attacks that
dramatically increase the strength of the electric shocks they deliver and, in
so doing, has confirmed a 200-year-old observation by famous 19th century
explorer and naturalist Alexander von Humboldt.
............................
n a legendary account the famous 19th century explorer and naturalist
Alexander von Humboldt recounted a dramatic battle between horses and electric
eels that he witnessed on a field trip to the Amazon. In the following 200
years, however, there have been no scientific reports of similar behavior on
the part of the eels, suggesting that perhaps von Humboldt exaggerated.
Last year, Vanderbilt
University biologist Kenneth Catania accidentally discovered that, under
certain conditions, the electric eels that he has been studying will react even
more dramatically than von Humboldt described: When cornered by a threatening
object that is partially submerged, they will often attack by raising up out of
the water, pressing their chin against the object's side and administering a
series of powerful electrical shocks.
Catania, who is the
Stevenson Professor of Biological Sciences, has included a description of this
behavior, an assessment of its effectiveness and an explanation of the
evolutionary advantages it provides the eels in the paper "Leaping eels
electrify threats supporting von Humboldt's account of a battle with
horses," published online this week in the Proceedings of the
National Academy of Sciences early edition.
"The first time I
read von Humboldt's tale, I thought it was completely bizarre," said
Catania. "Why would the eels attack the horses instead of swimming
away?"
The biologist keeps
the eels he studies in large tanks. Initially, he used a net with metal rim and
handle to transfer the eels from one place to another. "In hindsight, it
probably wasn't the best design to use with electric eels," he
acknowledged. However, it was a serendipitous choice. As he scooped up the
larger eels he found that every so often, an eel would stop trying to evade the
net and attack it by leaping out of the water while pressing its chin to the
handle, all the while generating a series of high-voltage pulses. (He was
wearing rubber gloves so he didn't get shocked.)
In a previous study,
Catania found that eels interpret small conductors as prey. In the case of the
metal-rimmed net, the eels seem to interpret the large conductor emerging from
the water as a potential predator. Catania described the eel's defensive behavior
as "both literally and figuratively shocking."
Catania's previous
research has also shown that that when eels attack a free-swimming fish, they
hit it with a high-frequency volley of millisecond pulses that don't fry the
fish, but instead stimulate the nerves that control its muscles and cause them
to contract -- freezing up the prey with the same mechanism of a TASER. Of
course, like a TASER, the eel's pulses inevitably activate sensory nerves that
cause pain. Causing pain is not so useful for catching prey, but like an
electric fence, it is just the ticket for deterring a predator.
Catania designed a
series of experiments specifically to determine what is happening with this
newly described "shocking leap" behavior.
First, he determined
that the eels ignore most things that do not conduct electricity, which makes
sense because living things typically conduct electricity.
By hooking a voltmeter
and then an ammeter to an aluminum plate, Catania was able to measure the
nature and strength of the electric impulses the eels were producing as they
leap up the conductor. He found that both the voltage and the amperage produced
by the eels increased dramatically as the eel leaped higher on the target.
When the eel is fully
submerged, the power of its electrical pulses is distributed throughout the
water. When the eel's body extends out of the water, however, the path that the
electrical current travels goes from its chin directly into the target. Then
the electric current travels through the target until it can exit back into the
water where it travels back to the eel's tail, completing the circuit.
"This allow the
eels to deliver shocks with a maximum amount of power to partially submerged
land animals that invade their territory," Catania said. "It also allows
them to electrify a much larger portion of the invader's body."
To visually illustrate
this effect, the researcher painstakingly covered a plastic arm and a plastic
alligator head with a conductive metal strip and a network of LEDs. When an eel
attacks these targets, the electrical pulses it generates cause the LEDs to
light up brightly.
"When you see the
LEDs light up, think of them as the endings of pain nerves being stimulated.
That will give you an idea of how effective these attacks can be," Catania
said.
(In the von Humboldt
story, two horses were stunned and drowned in the first five minutes of the
skirmish with the eels.)
Catania found that his
eels most often attacked when the water in the aquarium was lowered, probably
because they felt cornered. Much of the Amazon basin, where the electric eels
live, is under water during the rainy season but, during the dry season, the
water recedes leaving many ponds and oxbows which could restrict the eels'
freedom of movement and make them vulnerable to attacks by land predators.
Despite their power,
the pulses that the eels produce while fully submerged might not be sufficient
to discourage a hungry terrestrial predator if the predator can keep most of
its body out of the water. "If you put your fingers in the water when the
eel generates a pulse, you can barely feel it. If you put your whole hand in
the water, you feel it a bit more strongly," Catania said.
In addition, in some
locales electric eels are known to breed during the dry season and might benefit
from having an effective way to protect their young.
The eels' leaping
behavior likely evolved in steps, Catania suggested. Simply getting close to
the target would increase the effectiveness of its electroshocks. Making direct
contact with the intruder would further increase the power of the impulses, as
would making contact above the water. Once its head is above the water, then
the further up the eel goes, the more power is directed to the threat.
"Each stage
provides a successive advantage, suggesting how it may have evolved," he
has concluded.
As far as von Humboldt
goes, "it seems reasonable to suggest that [he] observed a similar eel
behavior on March 19th of 1800," Catania said.
Story Source:
The above post is
reprinted from materials provided byVanderbilt University. The original item was written by David
Salisbury. Note: Materials may be edited for content and length.
Journal Reference:
1.
Kenneth C. Catania. Leaping eels electrify threats, supporting
Humboldt’s account of a battle with horses. PNAS, June 6, 2016
DOI:10.1073/pnas.1604009113