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BBC: Bizarre newt uses ribs as weapons

Jennewt

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I've posted the text below, but the real treat is the photos. See:
http://news.bbc.co.uk/earth/hi/earth_news/newsid_8212000/8212623.stm

Matt Walker
One amphibian has evolved a bizarre and gruesome defence mechanism to protect itself against predators.
When attacked, the Spanish ribbed newt pushes out its ribs until they pierce through its body, exposing a row of bones that act like poisonous barbs.
The newt has to force its bones through its skin every time it is attacked, say scientists who have described the form and function of the barbs in detail.
Yet this bizarre behaviour appears not to cause the newt any ill effects.
The ability of the Spanish ribbed newt to expose its rib bones was first noticed by a natural historian in 1879.
But scientists have now used modern photographic and X-ray imaging techniques to reveal just how the animal does it.

And what they discovered is even more gruesome than they imagined.
When the newt becomes agitated or perceives a threat, it swings its ribs forward, increasing their angle to the spine by up to 50 degrees.
As it does this, the newt keeps the rest of its body still.
"The forward movement of the ribs increases the body size and stretches the skin to the point of piercing it," says zoologist Egon Heiss of the University of Vienna in Austria.
The tips of the newt's ribs then stick outside its body, like exposed spines.

But there is more to the newt's defence, Heiss and his Vienna-based colleagues report in the Journal of Zoology.
"When teased or attacked by a predator, [the newt] secretes a poisonous milky substance onto the body surface. The combination of the poisonous secretion and the ribs as 'stinging' tools is highly effective," says Heiss.
The impact on any predator can be striking, particularly if they try to bite the newt or pick it up using their mouth.
Then the poison in almost injected into the thin skin within the mouth, causing severe pain or possibly death to the attacker.

As well as elucidating the spear-like shape of the ribs, and exactly how the ribs swing forward and protrude, the scientists have demonstrated that the bones must break through the newt's body wall every time the amphibian evokes the defence response.
Initially, it was thought that the ribs may passively emerge through pores, rather than be actively driven through the body wall.
Surprisingly, the newt, which is related to other newts and salamanders, appears to suffer no major ill effects, despite repeatedly puncturing its own body and exposing its rib bones.
"Newts, and amphibians in general, are known to have an extraordinary ability to repair their skin," says Heiss.

"Anyway, if this newt can avoid being eaten in some cases, this surely has a positive influence."
It also seems that the newt is immune to its own poison, which is normally confined to glands in the newt's body.
When the newt wounds itself by exposing its ribs, the poison can seep into its body tissue, again apparently with no ill effects.
Heiss now hopes to investigate which compounds are in the poison.
 

John

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Actually Egon Heiss is a member of this forum. He joined in 2007 but hasn't logged in to his account since then - I am sure he has been back a few times though.
 

Jennewt

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I wrote to Egon, and he's been kind enough to allow me to use his photos on CC.:happy:
 

fishkeeper

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The ribs rotating forward explains a lot. When you pick them up midbody and press gently some instead of squirming tense up and you can feel the rib tips(this is not the case on an individual who merely wriggles and tries to escape). I've never actually seen one hold a position like that and wonder what kind of prodding must have provoked that response.

Two remaining questions(at least for me).

1. How potent is this newts toxin compared to other species?

2. How many predators can overcome the defenses of an adult newt? This seems like it could be particularly effective against snakes...but likely useless against an invertebrate predator such as a water scorpion(granted an adult of this sp. is probably safe from this just by sheer size). Does this defense make this newt better protected than other species?(for example, T. marmoratus and Salamandra that share its range). Why no aposematic coloration?
 

Azhael

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Two remaining questions(at least for me).

1. How potent is this newts toxin compared to other species?

2. How many predators can overcome the defenses of an adult newt? This seems like it could be particularly effective against snakes...but likely useless against an invertebrate predator such as a water scorpion(granted an adult of this sp. is probably safe from this just by sheer size). Does this defense make this newt better protected than other species?(for example, T. marmoratus and Salamandra that share its range). Why no aposematic coloration?

As far as i know the toxin is indeed very potent, but as with most of these animals, the quantities in which it´s produced are rarely problematic. If i remember properly, being stung by a P.waltl rib merely produces some inflamation, numbness and perhaps some pain, but is nothing to really worry about.

By large, the most common predators of P.waltl would be herons and such-like, and they don´t seem to have problems, i suposse, mainly, because the newt is dead before it´s swallowed. Natrix maura predates on them too, and seems to be resisitent to most if not all Salamandridae toxins. Water scorpions are no thread whatsoever for a metamorphosed P.waltl.
The reason for a lack of aposematic coloration(except for the orangy dorsal spots that mark the punctuation areas) is probably due to the habitat of this newts, which tend to inhabit rather cloudy and muddy waters where colour may be less important, and their conspicuous coloration is surely of great help.
 

fishkeeper

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Well, lets compare perhaps Pleurodeles to Taricha....the currently claimed most toxic caudate. Some Thamnophis can eat them with impunity. Do you suppose that they could also eat Pleurodeles?(this I assume would be determined by whether or not the skin toxins are biochemically similar enough). Likewise, would Natrix maura die eating a Taricha?

Herons generally swallow their prey whole...but a slightly prickly newt is nothing compared to some other meals they've been known to ingest...such as catfish.

You are probably right in that they simply prefer to remain inconspicuous. That can follow that either the ribs are really not that effective, or whatever is affected by them is not going to pay attention to warning colors anyway.


Oh yes, has anyone here who's played with Tylototriton on Echinotriton(close relatives of Pleurodeles and apparently with the same defence?) anything to add to this? Do they react to being picked up in a similar way?
 

Nathan050793

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Oh yes, has anyone here who's played with Tylototriton on Echinotriton(close relatives of Pleurodeles and apparently with the same defence?) anything to add to this? Do they react to being picked up in a similar way?

When I've picked my Tylotortion up by their midsection I've never had much of a reaction. I think being CB and use to occasional handling plays a role. I'm sure WC Tylos would be a different story. I too am curious to see if anyone has encountered this defense.
 

michael

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I friend of mine got nailed once by a P. waltl. He said he squeezed to hard and got nailed. He said it hurt more than a hornet sting and burnt for about 1 week. He didn't get medical attention.

I've bare handed thousands of P. waltl and never been nailed. My guess is you have to get them real mad or squeeze fairly hard.
 

Otterwoman

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Wow, these newts are amazing. Rib-shooting, outer-space explorers..maybe that's why NASA sent them up, to protect us from aliens with their amazing poisonous ribs. They'll think all earth creatures are that dangerous and keep their distance.
 

sergé

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Not many people will ever see this behaviour in captivity. Then you really have to irritate the animal.

However, it does not save pleurodeles in the wild. Once I caught a Natrix maura in southern Spain who immedeatly vomitted his prey. It was a large Pleurodeles and it came out head first, which means the snake had eaten the newt starting with the tail; so with the ribs as a pretty difficult to take obstacle.
 

fishkeeper

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Just the same Taricha are eaten by Thamnophis despite a very effective chemical defense. Like Taricha, Pleurodeles defense doubtlessly works against other predators(shrews/other mammals?) otherwise it would soon cease to exist.

But still wondering what would happen if they encountered new predators...Taricha vs Natrix or Pleurodeles vs Thamnophis?
 
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