How this deadly, rabbit-sized rodent chooses its poison
Researchers uncover how this unique mammal defends itself from predators
As if the idea of a giant rat wasn’t weird enough, a group of scientists have discovered that the African crested rat, a rabbit-sized rodent whose fur carries a poison strong enough to fell an elephant, cultivates its toxic coat by chewing on the bark of the poison arrow tree (Acokanthera schimperi). While the toxins are still in its mouth, it licks its fur, making it the only mammal known to sequester plant toxins as a chemical defence from predators.
The scientists, which came from the University of Utah, National Museums of Kenya and the Smithsonian Institution, placed the rats in a specially built enclosure, to observe their behaviour. They watched as the critters gnawed on the plants to draw out the toxin, then licked and chewed the poison into specific regions of their fur.
When offered different plant branches, the rats tended to coat themselves with cardenolides (bitter toxins that cause cardiac arrest) found in the poison arrow tree. The animals didn’t always interact with the plants when offered, sometimes sniffing and nibbling here and there without coating their fur, perhaps judging how harmful the poison could be with their keen sense of smell. 9hen threatened or eZcited, the rats flare their fur, revealing the specialised hairs that contain the poison.
Describing this defence, Dr Sara Weinstein, lead author of the paper and disease ecologist at the University of Utah, said that any animal that attacks the rat will get “a mouthful of these really potent toxins”, which can lead to death or sickness. Predators that survive the experience will give the rodents a wide berth in the future.
This defensive behaviour had only been seen in one rat before, but now Weinstein and her colleagues have studied 25 of the rodents, and recorded chewing and/or anointing behaviour in 10 of them. “The patterns we were seeing in many individuals proved it wasn’t just a freak occurrence,” she said. “We know that this is behaviour that they seem to do consistently.”
The team also discovered that the animals were sociable, and would interact with each other when placed in the enclosure. This was a surprise, as the rats were previously thought to be solitary. Future work will investigate both biochemical and behavioural factors of these intriguing creatures. Using DNA sequencing, we could learn how African crested rats (and even their fleas) remain unaffected by this poison. Studying their social structures could reveal new information about the rats’ relationships.