Frog Has Retractable Claws Like Wolverine

Photo: N. Iwai

This is one frog you don’t want to meddle with; Just check out the pinchers on this thing! The Japanese Otton frog, Babina subaspera, is one of the only species of frog in the world that possesses retractable claws like a cat.

Each of its spines is contained within a sheath and can be pushed out the front of the digit, but not without puncturing the skin. In other words, the frog has to inflict self-harm to use the spines. In this way, the frog might be more aptly compared to the comic book superhero Wolverine than to a cat.

So there’s a catch to having daggers for thumbs, and perhaps it’s for this reason that the frogs don’t often unsheath their spines for researchers to observe. In fact, the true purpose of the frog’s claws have largely remained a mystery to science. That is, until now.

Researcher Noriko Iwai of the University of Tokyo decided to get to the bottom of it, reports New Scientist. She set up hidden cameras to observe Otton frogs doing their thing in the wild, with some shocking results.

Although both sexes of Otton frogs possess claws, males’ spines tend to be longer, thicker and sharper than those of females. This provided some clues about what they were being used for, but Iwai had to see for herself.

It turns out that males use them to fight one another, in battles that understandably often turn bloody. The purpose? To win over the rights to breed with females in the territory, of course. But that’s only the half of it. Male Otton frogs also make for rather abusive lovers, using their spines to latch onto females while they mate. Females often carry the wounds to prove it.

It may not make for a very charming love story, but it does reveal some fascinating clues about how and why these claws evolved. Because both sexes possess claws, even though females don’t appear to use them, it’s possible that they originally evolved for a purpose that has since become obsolete. Iwai hypothesizes that at some point the use of the claws in male-to-male battles must have usurped their original purpose. This, in turn, caused the males to get much larger than the females; too large, in fact, which made mating difficult. It was then that the claws were also used to get a better grip on females during the mating process.

Interestingly, the Otton frog isn’t the only amphibian that can produce a weapon by self-harming. Some newts and salamanders can push their ribs out for use as swords, for instance. Perhaps the most brutal Wolverine-like amphibian, however, is the hairy frog of Cameroon, which actually breaks the bones in its hands to produce claws. Ouch!

By Bryan Nelson

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