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Thursday, August 4, 2011

The rat that wears a protective coat of deadly toxin made out of bark from a poisonous tree

-The Crested Rat from East Africa is the first mammal known to acquire lethal toxin from a plant

By Daily Mail Reporter

Avoid: The Crested Rat has deadly hairs filled with poison obtained from the bark of a toxic tree. It is the first mammal known to acquire lethal toxin from a plant

A species of rat coats itself in deadly toxin that it obtains by gnawing on a poisonous tree, scientists have discovered.

The Crested Rat - Lophiomys imhausi - from East Africa is the first mammal known to acquire lethal toxin from a plant.

To protect itself from predators, the creature chews the roots and bark of Acokanthera 'poison arrow trees' to extract the poison ouabain.

Bushmen in Kenya use the same poison to tip arrows which can fell an elephant.

In the case of the Crested Rat, the poison is absorbed into special lampwick-like hollow hairs on the animal's flanks.

When attacked, the rat puts on a dramatic fur-bristling display. Any predator that fails to get the message and takes a bite lives to regret it, or dies from heart failure.

Dogs have been known to collapse and die rapidly after biting a Crested Rat. Others that have survived an encounter shy away from the creature, according to local reports.

Researcher Dr Jonathan Kingdon, from Oxford University, said: 'At between 40cm and 50cm long, the Crested Rat looks quite innocuous as it clambers about in rocky, wooded valleys in Kenya and the Horn of Africa.

'But once disturbed or attacked the long fur on its flanks parts to expose a vivid black and white pattern around a leaf-shaped tract of peculiarly specialised hair, almost as if it is 'daring' a predator to take a bite of these poisoned hairs.'

Many species of tree frog use the same trick of employing plant toxins to make them poisonous to predators, but the trait has never before been documented in a mammal.

The scientists observed a wild-caught rat chewing Acokanthera bark and roots, mixing the ouabain poison with its saliva and selectively applying the spittle to the hollow hairs.

They were astonished by what they discovered when they examined the animal's poison hairs in the laboratory.

Professor Fritz Vollrath, another member of the Oxford University team, said: 'None of us had ever seen complex hair such as these with a latticework for the wall and a bundle of fine fibres for the core.

'It was surprising how effectively the hair was in "wicking-up" liquids, and then holding them fast. While the function of a reservoir for the poison was clear, we shied away from testing it by chewing a hair.'

The Crested Rat appears to be completely immune to ouabain, which is well known for its heart-arresting properties.

For centuries doctors have used tiny doses of the poison to stimulate weak hearts.

The scientists hope learning more about the chemistry and genetics of the Crested Rat's immunity could lead to new medicines for humans.

The research is published in the journal Proceedings of the Royal Society B.



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