Magazine article Science News

Hormone Still Rules No-Tadpole Frogs

Magazine article Science News

Hormone Still Rules No-Tadpole Frogs

Article excerpt

Skipping most of the tadpole business, a coqui frog hops out of the egg as a miniature adult, smaller than a pea. Even so, it doesn't escape the king of tadpole chemistry, thyroid hormone, say Canadian researchers.

In most mainland U.S. frogs, a surge of thyroid hormone tells a tadpole to grow up into a frog shape. However, hundreds of other frog species, mostly in the tropics, have lost the tadpole stage.

"How do you get rid of a whole life stage?" wonders Richard P. Elinson of the University of Toronto.

One scenario would be to escape thyroid hormone control. Previous work had shown that coqui frogs still need the hormone to form proper rumps, but biologists had speculated that it had little other function.

Not so, report Elinson and Elizabeth M. Callery of the State University of New York at Stony Brook. While still in their eggs, coqui frogs undergo a metamorphosis ruled by thyroid hormone, the researchers argue in a paper scheduled for the March 14 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES. "We propose a new model for the evolution" of frogs that develop directly, they say.

The apricot-size coqui frogs set the Puerto Rican dusk vibrating with the "co-key, co-key" call of males. "It's very high-pitched, very loud, very bright--it's wonderful," Elinson recalls. Females that agree lay clear eggs on a dry spot and hop away, leaving the males to sit on the clutch until the eggs hatch in about 3 weeks. Eggs can dry out fast, so coqui males leave their clutch only to find a quick meal and to defend the eggs from foraging males. …

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