Quirks & Quarks

This gorgeous African rat combs poison into its fur to deter predators

Researchers observed the rats chewing poison bark, and don't know how they are unaffected

Researchers observed the rats chewing poison bark, and don't know how they are unaffected

The African crested rat is the only mammal known to sequester lethal plant toxins (Stephanie Higgins)

Originally published on November 28, 2020.

A team of researchers has observed a unique behaviour in a mammal more typical of insects. Biologist Sara Weinstein and her colleagues saw African crested rats in Kenya chewing poisonous tree bark, and combing the toxin into specialized hairs on their coats.

Their study confirmed a older hypothesis that the rats are be sequestering toxins from the bark of a tree for defence against predators.

At first glance, the African crested rat looks like a cute, furry, grey rabbit with a little skunk mixed in. At about a kilo in mass, it's one of the larger and more attractive species of rat. 

Weinstein is a Smithsonian-Mpala postdoctoral fellow at the University of Utah in Salt Lake City. 

Sara Weinstein (left) and colleague Katrina Nyawira (right) in front of Acokanthera schimperi, the poison arrow tree (Submitted by Stephanie Higgins)

A mouthful of toxin

The rat harvests the toxin from a tree species called Acokanthera schimperi, known locally as the poison arrow tree, so named because its poison has long been used on the tips of hunting weapons.  The bark contains an extremely potent toxin known as a cardenolide, similar to compounds found in monarch butterflies and cane toads.

The toxin affects muscle and nerves, and can ultimately result in heart failure for most animals that come into contact with it. 

The crested rat chews on the leaves of the poison arrow tree. Sara Weinstein

Armed and dangerous

After the rat chews on the toxic bark, it spreads its now toxic saliva on specialized hollow and porous hairs that run in a band down the side of the animal. When the rat is threatened, these hairs stand up, revealing black and white stripes underneath. The researchers think these stripes serve to alert predators like leopards and hyenas that biting would be unwise.

The rat licks poison into specialized porous hairs, seen here alongside typical hairs (Sara Weinstein)

One outstanding mystery for the researchers is how the rat avoids poisoning itself as it extracts the toxin from the tree bark. 

The African crested rat is the only mammal known to sequester lethal plant toxins. During this study researchers were also surprised to discover the animals snuggling together, when they were previously believed to be solitary animals. (Stephanie Higgins)

 

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