The tiny poison frogs of Madagascar and the =
Americas get=20
their chemical weapons from toxic compounds known as=20
alkaloids. A new study shows that distantly related =
frogs in=20
the two regions obtain identical alkaloids from ants =
and other=20
arthropods, suggesting that similar chemical defenses =
can=20
evolve independently.
 |
Yellow means stop. The skin of South =
American=20
golden poison frog (Phyllobates =
terribilis)=20
contains enough toxin to kill 100 people. =
CREDIT: Valerie Clark=20
|
The four families of poison frogs--found in =
Australia,=20
Madagascar, and Central and South America--harbor some =
of the=20
world's deadliest animals. One thumb-sized species =
from=20
Colombia holds enough poison in its skin to kill 10 =
humans.=20
The frogs' toxic punch comes from alkaloids, a group =
of=20
bitter-tasting organic compounds that includes =
strychnine and=20
nicotine. Because most poison frogs can't manufacture =
their=20
own alkaloids, the source of their toxins was, until =
recently,=20
a mystery. Last year, researchers discovered that =
poison frogs=20
in Panama most likely get their alkaloids by consuming =
toxic=20
ants and a species of millipede.
Could similar =
arthropods=20
be the source of alkaloids for other poison frog =
species=20
elsewhere in the world? To find out, a team led by =
Valerie=20
Clark, a graduate student now at Cornell University in =
Ithaca,=20
New York, tested frogs and arthropods collected from=20
Madagascar. Of 81 alkaloids they detected in the =
frogs, seven=20
also showed up in the amphibians' arthropod prey, =
suggesting=20
that these frogs, like their Panamanian counterparts, =
get=20
their toxins from their diet. Although the Malagasy =
frogs and=20
their arthropod prey are not closely related to those =
in=20
Central and South America (with the exception of one =
millipede=20
and possibly one ant species), the frogs shared 75 =
percent of=20
their alkaloids. The fact that these shared alkaloids =
are not=20
found in other members of the Malagasy and American =
frog=20
families suggests that they did not evolve this method =
of=20
chemical defense from a common ancestor. Rather, it =
seems that=20
poison frogs in the two regions have independently =
evolved the=20
use of the same arthropod-derived alkaloids in =
chemical=20
defense, the team reports online this week in =
Proceedings=20
of the National Academy of Sciences.
"The fact that the chemicals are more-or-less the =
same is=20
striking," says Thomas Eisner, a chemical ecologist at =
Cornell=20
University. "It's a remarkable case of convergence" =
that shows=20
just how ingenious organisms are in the way they "play =
around=20
with chemicals."
--FIONA PROFFITT
Related sites
Clark's =
home=20
page
All=20
about poison frogs=20
