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Spitting  kobra melacak pertama , memprediksi kemudian

Spitting  kobra semprotkan  racun di mata korban mereka dengan akurasi yang luar biasa , tapi bagaimana mereka mencapai akurasi ini ketika mereka tidak bisa mengarahkan  racun nya  ? Para peneliti telah menemukan bahwa kobra awalnya melacak gerakan mangsa mereka , tetapi pada saat ketika mereka meludah , mereka memprediksi di mana mata korban dalam 200 milidetik ...read more

Spitting cobras track first, predict
later

Date:

May 15, 2010

Source:

Journal of Experimental Biology

Summary:

Spitting cobras spray venom in the eyes of their victims with remarkable
accuracy, but how do they achieve this accuracy when they cannot steer the jet
of venom? Researchers have found that cobras initially track their prey's
movements, but at the moment when they spit, they predict where the victim's
eyes will be 200 milliseconds in the future and aim there.

...................................

Most venomous snakes are legendary for their lethal bites, but not all.
Some spit defensively. Bruce Young, from the University of Massachusetts
Lowell, explains that some cobras defend themselves by spraying debilitating
venom into the eyes of an aggressor.

Getting the chance to work with spitting cobras in South Africa, Young took
the opportunity to record the venom spray tracks aimed at his eyes. Protected
by a sheet of Perspex, Young caught the trails of venom and two things struck
him: how accurately the snakes aimed and that each track was unique. This
puzzled Young. For a start the cobra's fangs are fixed and they can't change
the size of the venom orifice, "so basic fluid dynamics would lead you to
think that the pattern of the fluid should be fixed," explains Young.

But Young had also noticed that the snakes 'wiggled' their heads just
before letting fly. "The question became how do we reconcile those two
things," says Young, who publishes his discovery that the snakes initially
track their victim's movement and then switch to predicting where the victim is
going to be 200 milliseconds in the future in the Journal of
Experimental Biology.

Young remembers that Guido Westhoff had also noticed the spitting cobra's
"head wiggle," so he and his research assistant, Melissa Boetig,
traveled to Horst Bleckmann's lab in the University of Bonn, Germany, to find
out how spitting cobras fine-tune their venom spray. The team had to find out
how a target provokes a cobra to spit, and Young was the man for that job, "I
just put on the goggles and the cobras start spitting all over," laughs
Young.

Wearing a visor fitted with accelerometers to track his own head movements
while Boetig and Westhoff filmed the cobra's movements at 500 frames/s, Young
stood in front of the animals and taunted them by weaving his head about. Over
a period of 6 weeks, the team filmed over 100 spits before trying to discover
why Young was so successful at provoking the snakes.

Analyzing Young's movements, only one thing stood out; 200 ms before the
snake spat, Young suddenly jerked his head. The team realized that Young's head
jerk was the spitting trigger. They reasoned that the snake must be tracking
Young's movements right up to the instant that he jerked his head and that it
took a further 200 ms for the snake to react and fire off the venom.

But Young was still moving after triggering the snake into spitting and the
snake can't steer the stream of venom, so how was the cobra able to
successfully hit Young's eyes if it was aiming at a point where the target had
been 200 ms previously? Realigning the data to the instant when Young jerked
his head, the team compared all of the snakes' head movements and noticed that
the cobras were all moving in a similar way. They accelerated their heads in the
same direction that Young's eyes were moving. "Not only does it speed up
but it predicts where I am going to be and then it patterns its venom in that
area," explains Young.

So spitting cobras defend themselves by initially tracking an aggressor's
movements. However, at the instant that an attacker triggers the cobra into
spitting, the reptile switches to predicting where the attacker's eyes will be
200 ms in the future and aims there to be sure that it hits its target.







Story Source:

The above story is based on materials provided
by Journal of Experimental Biology. The original article
was written by Kathryn Knight. Note: Materials may be edited for
content and length.







Journal Reference:

1.   
Westhoff, G., Boetig, M., Bleckmann, H. and Young, B.A.Target tracking
during venom 'spitting' by cobras.Journal of Experimental Biology,
2010; 213: 1797-1802 [link]

http://www.sciencedaily.com/releases/2010/05/100514074909.htm

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