The African crested rat, Lophiomys imhausi, has a seemingly unique defence mechanism.
Credit: Muséum d'histoire Naturelle
The African crested rat, Lophiomys imhausi paints its crest with poison that it uses to ward off predators.
Credit: Susan Rouse
BRISTOL: The African crested rat has been revealed as the first known mammal to use plant poison to defend itself, using the toxins as a weapon against would-be predators.
The peculiar East African rodent, Lophiomys imhausi, uses saliva to transport the toxin, Ouabain, from gnawed branches of the Poison-arrow trees onto its unique wick-like fur.
The unique ability of the rats to part their flank hair, exposing a striking black-and-white fur pattern, has long been known, this elaborate display alone could not explain the animal’s unpalatability to predators.
It turns out that it is the design of this specialised flank hair, and its ability to hold and dispense poison, that makes the difference, according to a group of East African and British scientists.
“Our Fourier transform infrared (FT-IR) pilot study of the compounds found inside the hairs strongly suggest the presence of ouabain,” writes lead author Jonathan Kingdon from Britain's University of Oxford, in the study to be published in Proceedings of the Royal Society B.
Hiding behind a toxic coat
Ouabain is a toxic compound found in the bark of Poison-arrow trees of the genus Acokanthera. The compound has long been used for poisoning arrow heads by East African hunters and as a clinical treatment against heart failure.
The multinational research team observed the behaviour of rats in the wild and captivity when exposed to Poison-arrow tree bark. They found the animals chewed the bark before applying the saliva to their parted flank hairs.
Interestingly, whilst many animals have evolved characteristics to perturb predator bites, the African crested rat appears to house a suite of protective counter measures in case of the inevitable.
Its armoured skull, dense thick skin and a fearless behaviour are characteristics that the research team suggest imply a reliance upon a form of deterrence that is fast-acting and more costly to the predator than the prey, the lethal toxin.
“Of special interest is the fact that the toxin is a functional component in normal animal - including human - physiology,” says Jonathan Kingdon.
“Both you and I regulate our body functions, notably heartbeats, involving minute quantities of ouabain-like chemistry.”
This suggests that further research into the rodent's resistance to ouabain could lead to human pharmacological applications, he added.
Deadly wick-like hair
The team examined the structure of the lateral line hairs found in the crest using both light electron microscopy and scanning electron microscopy.
They found that the central portion of the hairs main shaft showed a thin but strong perforated outer cylinder. Encased within the shaft where fibourous strands which act like a ‘wick’, drawing fluid up the structure.
“The hairs have evolved as they have by still incalculable increments to become possibly one of the most complex hair structures known among mammals,” Jonathan Kingdon told Cosmos Online.
