Rare Japanese frog species armed with spikesPublished On: Sun, Oct 21st, 2012 | New Species | By BioNews
A rare frog species is armed with combat-ready spikes which shoot straight from the fingers, like that of a comic book hero, says a Japanese scientist.
The discovery by Noriko Iwai, from the University of Tokyo, reveals how the Otton frog uses spikes which protrude from a false thumb for both combat and mating.
The study focused on the Otton frog whose habitat is the Amami islands of Southern Japan. Unlike most other frogs, the Otton has an extra digit-like structure, a trait it shares with the five-fingered Hypsiboas rosenbergi frogs of Latin America, the Journal of Zoology reports.“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,” said Iwai. “The digit encases a sharp spine which can project out of the skin, which fieldwork demonstrates is used for combat and mating.”
Iwai has studied the rare frogs since 2004 in order to understand the species’ distribution, breeding habits and range — all factors which will contribute to any conservation strategy, according to a Tokyo statement.
Once she began exploring how the Ottons use their pseudo-thumbs, Iwai discovered that while both males and females had the spike, it was only used by males.
Males were found to have larger pseudo-thumbs than the females and Iwai believes that the spikes evolved for anchoring to the female, known as amplexus, the Latin for embrace, during mating.
“While the pseudo-thumb may have evolved for mating, it is clear that they’re now used for combat,” said 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.
N. Iwai, Morphology, function and evolution of the pseudothumb in the Otton frog Journal of Zoology, 18 OCT 2012 DOI: 10.1111/j.1469-7998.2012.00971.x