Locating a poison

Certain types of poisonous frogs and birds may owe their powerful defensive systems to a diet of toxin-laden beetles. As the frogs and birds do not make the toxins themselves, it was long suspected they were coming from the animals’ diets. The exact dietary source is unknown, but researchers from the US working with a colleague from a rural bush village now believe a type of beetle may be responsible.

The family of compounds to which the poison involved belongs, known as batrachotoxin (BTX) - meaning frog toxin - has a steroid-like structure. BTX has a dramatic effect on the nervous system via binding specifically to sodium channels in nerve cells. The effect can swiftly paralyse and often kill the victim. Some BTXs are particularly potent, being used to coat tips of blow-darts for hunting. The frogs that produce those toxins are known as poison-dart frogs.

Following several years of research, Avit Wako a member of the team and native New Guinean, tracked down what he believed was the source of the toxins - beetles from the Melyridae family. These beetles were analysed and found to contain high concentrations of BTX. The researchers also discovered fragments of these small beetles in the stomachs of Pitohui birds in the region. Pitohui birds are toxic and carry BTXs in their skin and feathers; the presence of Melyridae beetles in their diet strongly suggests that they may be the birds’ toxin source.

Team leader John Dumbacher, from the California Academy of Sciences in San Francisco, told Chemistry World that almost nothing is known about the beetles. Exactly how the frogs and birds can eat the beetles and accumulate the toxins while remaining insensitive to them is unclear. Dumbacher hopes to continue research in this area. ’Now that we have a potential source of the toxins, we can feed the beetles to the birds in some of these experiments,’ he said.

Vikki Allen