Morse Toad: When amphibians tap their toes

Toe wiggling creates motions, vibrations that get potential prey moving

When some toad toes tap, maybe it’s the beat, not the motion, that matters.

WAGGLERS Fowler’s toads vibrate their hind toes when food shows up. Frogs and toads in at least seven families waggle their toes, though researchers are still figuring out what’s going on. J. Sloggett

PEDAL LURING | An adult cane toad waggles its hind toes when littler toads show up, an intriguing motion that draws bite-sized juveniles close enough to become a cannibal’s lunch. Video shown in real time, then slowed down. M. Hagman

TAP DANCE A Mozambique rain frog waggles its feet when offered a mealworm, and the sound recording (from both toes) indicates that the motion taps out strong vibrations, which could play a role in nabbing prey. Sloggett & Zeilstra. 2008 Animal Behaviour

The resulting vibrations could agitate insects and other little morsels, setting them wriggling and scuttling in a flurry of activity that triggers a toad’s known tendency to strike at moving prey, says entomologist John Sloggett of Groningen, the Netherlands.

Details of how a toad’s brain processes information about when and where to strike will require deep amphibian neuroscience. But Sloggett and Groningen ecologist Ilja Zeilstra propose that vibration deserves attention in the study of what’s up with all the toe wiggling among frogs and toads.

That study of toe motion surged in 2008, with two papers: a study in January’s Animal Behaviour on cane toads’ habit of “pedal luring,” and a paper by Sloggett and Zeilstra in the online version of the November Animal Behaviour.

Cane toads flutter their toes when small prey appear, and the intriguing pedal lure draws little cane toads closer to bigger cannibalistic ones, reported Mattias Hagman, now at Stockholm University in Sweden, and Rick Shine of the University of Sydney in Australia, in January.

Hagman and Shine studied a colony of captive cane toads for research on how to minimize damage to Australia’s native landscape as these big, poisonous toads invade. Hagman noticed that the arrival of crickets or a nearby aquarium full of bite-sized juveniles set the long middle toes of the adults’ hind feet waving.

To test the effects of toe waving, Hagman and Shine built a mechanical toe that could wiggle at various rates and affixed it to a taxidermy mount of a deceased toad. Waving the toe didn’t much interest the crickets. But the motion did entice clusters of the juvenile toads to move closer to the stuffed mount, Hagman and Shine reported.

Older cane toads near water could easily encounter youngsters clustering there during the dry season, Shine says. Dissecting more than two dozen adults from the wild, Hagman and Shine found that 64 percent of the adults’ meals had been even smaller toads of their own species.

“By understanding these interactions, we might be able to work out ways to turn cannibalism to our advantage,” Shine says.

Waving toes to create an alluring motion makes sense with visually responsive prey, says Sloggett. But for frogs and toads eating mainly invertebrates, which don’t respond much to gestures, maybe it’s the vibrations and subsequent frenzy of motion that matter, he and ecologist Zeilstra suggest in their new paper.

The two researchers keep frogs and toads as a matter of personal interest, and Sloggett even brought North American amphibians with him to Europe after he recently finished a project at the University of Kentucky in Lexington. Observation of some of those companions brings the total number documented to at least 13 species across seven frog and toad families, the team reports.

Getting information about an animal’s diet in the wild isn’t perfect, but several species are known to eat a lot of invertebrates. One such toe-wiggler, the Mozambique rain frog, Breviceps mossambicus, probably doesn’t prey on vertebrates because it has such a small mouth. This frog flexes its long middle toe when it catches sight of food, and by feeding a rain frog on a sheet of plastic, the researchers recorded strong vibrations from the toe tapping.

Toe flexing for useful vibrations “sounds plausible to me,” Shine says. “But the data are yet to be gathered.” And vibrations and motion can work together, Hagman says.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

More Stories from Science News on Life