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You talkin' to me? A male dart-poison frog (right) takes on RoboRana.

Hopping Mad

It's not easy to piss off a dart-poison frog. But after 50 years of trying, scientists have finally managed to get them fighting--with a little help from a trash-talking mechanical dummy. Their findings shed light on the how's and why's of amphibian aggression and may help researchers probe the neural basis of such behavior.

In the wild, dart-poison frogs are very territorial: Frogs that have staked out a good piece of ground will attack any rival calling on their turf. Yet scientists have had a hard time provoking fights during experiments. Most studies have involved playing recorded calls through a speaker. Confronted with an antagonistic speaker, a male frog will generally approach it, and occasionally hop on top. But the animals never attack the speaker, says Peter Narins, a neuroethologist at the University of California, Los Angeles.

Narins and colleagues crafted an artificial log with a speaker and a lifelike rubber frog (aka RoboRana) with an inflatable pouch that mimicked the frogs' throat sac. They put the log inside the territories of calling males in French Guiana. As expected, when the team merely broadcast calls through the speakers, males would come closer, but not attack. They also ignored RoboRana when the throat sac remained inflated or deflated while a call was broadcast. But when the team paired calls with throat sac movements like those made by calling frogs, the frogs put their best wrestling moves on the mechanical frog (see movie here). Narins now plans to investigate the neural basis of the aggressive reaction by measuring neural activity when frogs are goaded by RoboRana.

It's interesting that it takes both sound and sight to trigger the frogs' aggression, says Kyle Summers, an evolutionary biologist at East Carolina University in Greenville, North Carolina. While some vertebrates are ticked off by a combination of signals, others seem to have a shorter fuse: certain birds, for example, can be provoked by a mere tuft of feathers attached to a perch. That raises the intriguing question of why these different sensitivities evolved, Summers says.

Related sites
Peter Narins's site
Kyle Summers's site
More information on Epipedobates femoralis
Photos of E. femoralis