Little Froggy Jewels

Spent yesterday at the Madison Zoo, so here's a couple of neat shots:

Golfodulcean Poison Frogs (Phyllobates vittatus),
 Henry Vilas Zoo, Madison, Dane Co, WI 3/22/2014

These are Golfodulcean Poison Frogs (Phyllobates vittatus), endemic to Costa Rica and considered endangered.

Strawberry Poison Frog (Oophaga pumilio),Henry Vilas Zoo, Madison, Dane Co, WI 3/22/2014

This is a Strawberry Poison Frog (Oophaga pumilio), found commonly across the southern half of Central America.

They are both in the family Dendrobatidae, often called poison-dart frogs. The poison in question is a combination of batrachotoxins, which are extremely toxic organic alkaloids. This, of course, explains how such a small, otherwise defenseless little frog can survive being bright orange.

Their toxicity has been known to science for over 200 years, ever since Dendrobates tinctorius was described in 1799. What hasn't been known for very long is that certain birds, called Pitohuis, carry the same batrachotoxins as the frogs! (1) That was first reported in 1992, when a graduate student from the University of Chicago noticed that his hands turned numb after handling the birds. In 2000, a new species of toxic birds, Ifrita, was discovered, again in New Guinea, again with batrachotoxins. (2) And since then, at least one author has argued that the genus is polyphyletic, including species from several different genera in the Corvoidea. (3)

The initial discovery of the birds seemed to indicate an amazing example of convergent evolution, with two entirely unrelated groups producing the same complicated toxin. But these later two discoveries make that just a bit too difficult to resolve. Some species of insects are known to sequester plant toxins in their own tissues, making them distasteful -- Monarchs (Danaus plexippus) and Pipevine Swallowtails (Battus philenor)  are both well known for this. So the same biologist who published the first paper went searching, and found a group of beetles that produce this toxin, the Melyrid beetles. (4) They are widespread, not only in the tropics, but in North America and Europe as well. So it's now thought that the convergence entailed the ability to sequester these toxins rather than succumbing to them. Similar convergences have been noticed in insects, with members of at least 3 orders (Lepidoptera, Homoptera, and Coleoptera) all able to do the same with toxic chemicals in Milkweed sap.

That one discovery of toxic birds in a New Guinea jungle has initiated an entire forest of research, into everything from phylogeny and physiology to the possibility of Mullerian mimicry in birds. All because a single grad student paid attention to the world around him, and took the time to think about not only what was happening to him, but why it might be.

And that is science at its best.

(1) Dumbacher, J. P., Beehler, B. M., Spande, T. F., Garraffo, H. M., & Daly, J. W. (1992). Homobatrachotoxin in the genus Pitohui: chemical defense in birds?.SCIENCE-NEW YORK THEN WASHINGTON-, 799-799.

(2) Dumbacher, J. P., Spande, T. F., & Daly, J. W. (2000). Batrachotoxin alkaloids from passerine birds: a second toxic bird genus (Ifrita kowaldi) from New Guinea. Proceedings of the National Academy of Sciences, 97(24), 12970-12975.

(3) Jønsson, K. A., Bowie, R. C., Norman, J. A., Christidis, L., & Fjeldså, J. (2008). Polyphyletic origin of toxic Pitohui birds suggests widespread occurrence of toxicity in corvoid birds. Biology letters, 4(1), 71-74.

(4) Dumbacher, J. P., Wako, A., Derrickson, S. R., Samuelson, A., Spande, T. F., & Daly, J. W. (2004). Melyrid beetles (Choresine): A putative source for the batrachotoxin alkaloids found in poison-dart frogs and toxic passerine birds.Proceedings of the National Academy of Sciences of the United States of America, 101(45), 15857-15860.