African rodent uses 'poison arrow' toxin to deter predators

Aug 03, 2011
The African crested rat is the only mammal known that acquires its poison from a plant. The rodent masticates the poisonous bark of the Acokanthera tree and applies the mixture to its flank hairs, which absorb the poison like candle wicks. Credit: Susan Rouse

Woe to the clueless predator trying to make a meal of the African crested rat, a rodent that applies poisonous plant toxin to sponge-like hairs on its flanks, a discovery recently made by Jonathan Kingdon and colleagues from the National Museums of Kenya, the Wildlife Conservation Society, and University of Oxford.

In the only known instance of a mammal acquiring a lethal toxin from a plant for defense, the researchers have discovered where the African crested rat (or maned rat) gets its poison: the Acokanthera tree, the same source used by East African hunters for poison arrows.

The study appears online in the . The authors include: Jonathan Kingdon, Chris Holland, Tom Gheysens, Maxime Boulet-Audet, and Fritz Vollrath of the University of Oxford; Bernard Agwanda of the National Museums of Kenya; and Margaret Kinnaird and Tim O'Brien of the Wildlife Conservation Society.

"The African crested rat is a fascinating example of how a species can evolve a unique set of defenses in response to pressure from predators," said Dr. Tim O'Brien, Senior Scientist of the Society and a co-author on the study. "The animal and its acquired toxicity is unique among placental mammals."

Scientists have long suspected that the African crested rat is poisonous, primarily due to the animal's specialized behavior, such as exposing a black-and-white coloration on its flanks when threatened by predators, and accounts of dogs becoming ill or dying after encounters with rats. The new discovery concerns the nature of the chemical defense. Instead of producing poison itself—as is the case with poisonous mammals such as the duck-billed platypus and solenodon—the African crested rat finds its toxin (called ouabain) in tree bark.

Researchers from the Wildlife Conservation Society, the University of Oxford, and the National Museums of Kenya have discovered where the African crested rat (or maned rat) gets its poison: the Acokanthera tree, the same source used by East African hunters for poison arrows. Credit: Susan Rouse

The researchers confirmed the hypothesis by presenting a wild-caught rat with branches and roots of the Acokanthera tree. The rodent proceeded to gnaw and masticate the bark (avoiding the leaves and fruit) and apply the "slaver" on its flanks. Further, the research team employed electron microscopes to examine the unique structure of the flank hairs. In doing so, they found that the perforated cylindrical structure of the hairs facilitates the rapid absorption of the poisonous saliva. Interestingly, ouabain has also been used by doctors for centuries as a clinical treatment against congestive heart failure.

Besides its warning coloration and poisonous hairs, the African crested rat possesses a thick reinforced skull, thick vertebrae, and unusually tough skin, all protection for the small rodent that rarely grows to more than 2 pounds in weight.

Several mysteries about the enigmatic rodent remain, including how the animal uses poison without succumbing to it.

Explore further: Female color perception affects evolution of male plumage in birds

Related Stories

Toxic toll of rat poison on birds revealed

May 04, 2011

Rats might not be everyone's cup of tea, but you might want to think twice about reaching for the rat poison next time you come across one. While rat poison is brilliant at killing rats, it also spells danger ...

Smelling a rat to catch a rat

Mar 24, 2008

A novel experiment using laboratory rats to attract wild rats could pave the way for “rat perfumed” bait capable of reducing the millions of rats threatening New Zealand’s native species, say Massey ...

Recommended for you

User comments : 8

Adjust slider to filter visible comments by rank

Display comments: newest first

gmurphy
not rated yet Aug 03, 2011
It begs the question, how on earth did this sort of behaviour start?
DontBeBlind
1 / 5 (4) Aug 03, 2011
Another "evolved" animal.. Every time i read or hear something like this it reminds me of how they use to think the earth was flat and you could fall off the edge of it.
Isaacsname
5 / 5 (1) Aug 03, 2011
" In the only known instance of a mammal acquiring a lethal toxin from a plant for defense "

....says who ?

http://jinrui.zoo...MPP.html

http://jinrui.zoo...ant.html

http://www.behav....tion.pdf
gmurphy
not rated yet Aug 03, 2011
@Isaacsname, very interesting links, but that sort of behaviour could reasonably be explained by cultural transmission. According to the original researchers, the behaviour of this rat is "hard-wired": http://www.livesc...lls.html
jselin
not rated yet Aug 03, 2011
I think this could/should be considered tool use
natetuvkok
not rated yet Aug 03, 2011
It's Teemo, lol
Isaacsname
not rated yet Aug 03, 2011
@Isaacsname, very interesting links, but that sort of behaviour could reasonably be explained by cultural transmission. According to the original researchers, the behaviour of this rat is "hard-wired": http://www.livesc...lls.html


Good point. I would be curious how it would play out were they hand-raised in a lab setting.
Ethelred
5 / 5 (1) Aug 05, 2011
the earth was flat and you could fall off the edge of it.
Are you reffering to the Biblical claim that the Earth is a disc?

Sorry but your the one that is blind. Evolution has megatons of evidence supporting it. Whereas nothing supports a young Earth or a Great Flood. And just when was that alleged Great Flood?

Ethelred

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.