Rats use poison to get the better of their predators

Aug 15, 2011, 9:17 GMT

London - African crested rats make use of phytotoxins to ward off predators, British biologists have discovered.

The rodents masticate plant bark and then spread the poison released on their coats using their saliva. The poison is released at the least contact, leading to potentially fatal consequences for the predator.

These small relatives of the mouse make their hair stand on end when danger looms, recalling the behaviour of a porcupine more than that of a rat.

The danger for the predator lies not in the long outer hair, but in the lower, hidden levels of the coat running down from behind the ears to the rump. When the hair is raised, these areas are exposed, making contact hazardous to the predator more likely.

The team led by Jonathan Kingdon and Fritz Vollrath of the University of Oxford was able to observe how the rats gnawed at the bark of the shrub Acokanthera schimperi, chewed it and subsequently distributed it over the sides of their coat with their tongues.

The zoologists analysed these parts of the coat more closely and published their findings in the Proceedings of the Royal Society B.

Using an electron microscope, the researchers found thin fibres in the inner hair capable of absorbing the toxic mixture in the saliva like the wick of a candle.

They were able to detect the presence of a phytotoxin, a so-called cardenolide. This group of poisons includes ouabain, long used by indigenous African peoples to tip their arrows with poison for hunting.

The poison has differing effects for example on dogs, according to reports collected by the team. These range from a loss of coordination in the would-be predator right up to immediate heart failure.

Why the poison does not affect the crested rats themselves remains a mystery.