Tokyo: 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
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
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.