Nature's warning signs

In the laboratory, all bottles containing toxic substances must carry a label with a warning sign of globally uniform appearance. In nature, different species that produce toxins to make themselves unpalatable to predators are often found to share unified warning signs, such as conspicuous, brightly coloured patterns. While the uniformity in the lab is due to legal regulations and serves the safety of the person who might ingest the poison, the natural phenomenon, known as M?llerian mimicry, arises from the evolutionary advantage it confers not to the predator warned, but to the prey spared. If several species share the cost of the errors that predators make while learning to read the warning signs, each suffers less significant losses. UK researchers have now found an additional benefit to the sharing species.

John Skelhorn and Candy Rowe at the University of Newcastle, UK, fed chickens with red breadcrumbs treated with either quinine, or bitrex (an anti-nail-biting agent), or a combination of both, along with green breadcrumbs sprayed only with water. Within six trials, the chicks that were fed only one of the two bitter chemicals had learned to avoid the red crumbs. Surprisingly, the chicks exposed to a mixture of bitrex- and quinine-flavoured crumbs learned their lesson in half as many rounds. Moreover, in a test taken four days after the training, those chicks that had been exposed to two different bitter substances, were much better at avoiding the red crumbs than both single-flavour groups.

These results suggest that, on top of the shared-cost benefit, the sharing of a warning sign between prey species with different toxins provides additional protection, as it makes the warning sign more memorable. Essential lab safety, as invented by Nature a long time before IUPAC.

Michael Gross

J Skelhorn and C Rowe, Proc. R. Soc. London, Ser. B, 2004 (DOI: 10.1098/rspb.2004.2953)