Duelling with a Flick-Knife Frog

Flick knife (by yunalee)

A Japanese researcher (and presumptive anime fan) has revealed how a frog can flick out sharp spikes from a false thumb for both combat and mating.

Noriko Iwai from the University of Tokyo, studied the Otton frog (Babina subaspera), on the Amami islands in southern Japan.  Unlike most frogs, Otton has a fifth digit, a sort of pseudo-thumb, containing the switchblade spikes.  Science Daily reports that the thumb serves mainly to hang onto the female in the muddy throes of amphibian love-making:

“While the pseudo-thumb may have evolved for mating, it is clear that they’re now used for combat,” said Dr Iwai. “The males demonstrated a jabbing response with the thumb when they were picked up, and the many scars on the male spines provided evidence of fighting.”

The conditions on the Amami islands make combat, and the need for weaponry, a key factor for the frogs’ mating success. Individuals fight over places to build nests, while the chances of a male finding a mate each night are rare, thus the ability to fight off competitors may be crucial.

Sadly, the frogs don’t face off as in the rumble scene from “West Side Story”  (or, to stick with anime, like Spike versus Vicious).  Instead, they go in for the desperate clinch and then dirty-box:

Armed charmer

Perhaps unfortunately, the comic book hero image is slightly dented by the frogs’ fighting style. Rather than dueling with thumb spikes the males wrestle each other in an embrace, jabbing at each other with the spines. This fighting style helps confirm the theory that the spines were original used for embracing mates.

Also sorry to say, Dr. Iwai’s closeup of the weaponry suggests sharpening may be in order.

N. Iwai. Morphology, function and evolution of the pseudothumb in the Otton frog. Journal of Zoology, 2012; DOI: 10.1111/j.1469-7998.2012.00971.x