Japan's Otton Frogs Have Retractable Spines in False Thumbs
Posted on October 18, 2012
Dr. Noriko Iwai from the University of Tokyo has discovered that the Otton frog (Babina subaspera) has retractable knife thumbs. The Otton lives on the Amami islands of Southern Japan. The frogs don't fence with the knife thumbs. Instead dueling male Otton frogs wrestle with each other and try to viciously jab each other with their thumb spines.
Dr. Iwai said in the announcement, "Why these 'fifth fingers' exist in some species remains an evolutionary mystery, but the extra digit of the Otton is in fact a pseudo-thumb. The digit encases a sharp spine which can project out of the skin, which fieldwork demonstrates is used for combat and mating."
Dr. Iwai has been studying Otton frogs since 2004. She says males and females both have thumb spikes, but males have larger ones. She says males also used the spikes for anchoring to females during mating.
Dr. Iwai says, "While the pseudo-thumb may have evolved for mating, it is clear that they're now used for combat. 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."
A video of an Otton frog sitting in the darkness can be seen here and Otton frogs engaging in a brief fight can be seen here.
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