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S.F. researcher tracks poison over 9,500 miles

by louis bettencourt ( sfgate.com)
There stood Jack Dumbacher, innocently trying to trap a gorgeous bird of paradise in the mist net he'd set up for his research in a New Guinea forest, when the net entangled a flying stranger, all vivid orange and black.

The unwanted bird clawed Dumbacher's fingers, nipped them with its beak, and when the startled scientist put a bleeding finger to his mouth, he suddenly felt a burning, tingling sensation on his tongue and lips -- which soon became briefly numb.

The bird was a hooded pitohui (pronounced PIT-a-hooey), and the encounter in Papua New Guinea 15 years ago led the ornithologist to abandon his research into birds of paradise and to follow a mysterious, deadly poison that links the birds in the highland Papuan villages to frogs in the lowland South American jungles of Colombia -- and to beetles in both far-off habitats.

Link between birds, beetles

Dumbacher and his colleagues have now discovered that a family of beetles in New Guinea and their distant relatives more than 9,500 miles away, on the other side of the Pacific, are apparently responsible for the toxins in Dumbacher's pitohui birds -- the first poisonous birds discovered anywhere - - and Phyllobates terribilis, the poison-dart frogs of Colombia. The frogs got their name because the Choco Indians use the same poison to tip their arrows and blowpipe darts when they hunt for monkeys and other game animals.

Discovering the toxin in the pitohuis, and in a species of another genus of Papuan birds called Ifrita, marked the first example of chemical defenses that are known to have evolved in any of the world's birds, Dumbacher said.

Toxin's origin a mystery

"But we still don't know where that toxin really comes from," he said recently in his lab at the California Academy of Sciences in San Francisco. "All we know is that it's 250 times more poisonous than strychnine, more poisonous than curare, and 10 times more powerful than fugu, the puffer fish that gourmets in Japan risk their lives eating."

Dumbacher, the chairman of the academy's department of birds and mammals, is convinced that some species of birds use chemicals -- poisonous or foul- smelling -- to defend themselves against predators, just as many animals -- from skunks and coral snakes to monarch butterflies -- use specialized poisons or odors as defenses against prey. Still other animals mimic the coloration of the successful defenders and thus protect themselves by fooling their predators.

Two insightful colleagues

Dumbacher has reported his most recent beetle findings in the Proceedings of the National Academy of Sciences. Among his research colleagues are Avit Wako, an experienced and knowledgeable native naturalist in his own Papuan village of Herowana, who helped Dumbacher explore local lore and legend, and John W. Daly, a biochemist at the National Institutes of Health in Bethesda, Md., who is the world's leader in isolating novel chemicals -- both poisonous and benign -- from natural sources. Daly discovered the chemistry of the deadly pitohui toxin in the Phyllobates terribilis frog. The poison, a nerve-paralyzing neurotoxin, is called homobatrachotoxin.

As Dumbacher noted, "Carrying the toxin in its feathers and skin would certainly be a big boon for a bird that's only the size of a small jay -- giving it a major advantage in the struggle for survival where predators like snakes and hawks threaten it constantly."

It was Wako who told Dumbacher that the people of Herowana shun the pitohui as "rubbish birds" because of their stench and the fact that even touching them can cause disagreeable sensations. They are eaten only after extreme care is taken to remove feathers and skin, and even then, the meat must be carefully treated to have any use as food, Wako said.

Wako also told Dumbacher that his people have a word for the unpleasant numbing, tingling effects of contact with the pitohui birds. They call it nanisani, and they use the same word in talking about another poisonous bird of the region, the genus Ifrita.

For the birds, therefore, nanisani is a highly protective defense, as the people in the forests where the pitohui fly avoid hunting them -- leaving the birds largely unmolested, Dumbacher said.

"Wako is a most remarkable man," Dumbacher said, "for not only is he a highly knowledgeable naturalist, but he's also been alert to the progress other villages have made in gaining access to the outside world for trade and contact."

Improving access, comfort

As a result, Dumbacher said, Wako single-handedly dug out an entire airstrip along a flat stretch of land near his village, so that what had been a hard three-day trek through tough terrain is now only a few minutes from larger towns and trading centers. Wako also has built a small but comfortable -- and rainproof -- shelter as a kind of minihostel for ecotourists.

Daly, Dumbacher's biochemist colleague, had previously identified the toxin in the poison-dart frogs of Colombia. At first, the two scientists theorized that the birds and frogs -- two animals widely separated on the evolutionary tree -- had independently evolved the same nerve poison.

But recently Dumbacher found a species of Choresine beetle in the guts of the pitohui. The beetles carry high levels of the same toxin that fills the birds' feathers and skins -- strong evidence, Dumbacher said, that feeding on those beetles may endow the birds with their uniquely poisonous protection.

Whether the poisonous frogs of Colombia also feed on a distantly related Choresine beetle remains a mystery -- and political instability, paramilitary forces and drug warfare in that nation make it too dangerous for scientists to go beetle-hunting there, according to Dumbacher.

Even if the two species of beetles do turn out to be the source of the identical poison carried by frogs in Colombia and birds in New Guinea, another mystery is unresolved: What has made the beetles so toxic?

Independent evolution on two continents? A similar toxin-containing diet source -- plant or animal -- for the widely separated beetle species?

"There's plenty of mystery left," Dumbacher said.

E-mail David Perlman at dperlman [at] sfchronicle.com.

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