Magazine article Science News

Death Risk Drives Shocking Love Songs

Magazine article Science News

Death Risk Drives Shocking Love Songs

Article excerpt

The risk of getting killed often has a dampening effect on the silly excesses of courtship, but the opposite may have been true in electric fish.

The need to evade predators could have driven the electric serenades of knife fish to evolve from a simple zap ... zap ... zap to a variety of zippity doo-dahs, according to an analysis by Philip K. Stoddard of Florida International University in Miami. In the July 15 NATURE, he reports that a predator can't detect the complex signals as easily as the simple ones.

"Predators really have been a creative force," he says.

Knife fish mostly cruise murky water at night and emit weak signals to communicate and scan for obstructions. More than 100 species, which include predatory electric eels, roam the fresh waters of Central and South America. Another group, in Africa, evolved electrical signals independently.

Stoddard argues that ancestors of New World knife fish made a one-phase signal. He draws it as a single peak. Many modern fish have gone multiphasic, adding foothills and sunken gorges before and after that main peak.

At first, Stoddard suspected that female fancy had inspired complex signals, just as it sent male peacocks to fashion excess in tail feathers. Males and females typically differ in such exaggerated traits, Stoddard says, yet he saw fewer sex differences in fish than expected.

Electric eels and catfish home in on electric signals when they hunt small knife fish. To assess a typical predator's capabilities, Stoddard trained an eel named Sparky to swim toward electric signals. Sparky responded to one-blip signals about twice as often as he did to multiphasic signals. …

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