Even when predation does occur, pseudothumbs may not be effective

Even when predation does occur, pseudothumbs may not be effective against predators because they face inward and the projected spines can only attack something within their arms. Also, most of the Otton frogs did not aggressively attack humans with their pseudothumbs when captured; aggression occurred only when their chest was irritated, which can be considered a reflex related to male–male combat or amplexus. Thus, the possibility of pseudothumb use for obtaining food or protection is slight. The pseudothumbs of the male Otton frogs were sometimes wounded. This seemed to be because the spine pierced its sheath during use. Otton frogs jab their pseudothumbs into

their opponents so strongly that the spines emerge by cutting through the sheath. When the author pulled down SB203580 mw Selleck BI 2536 the sheath, the spine emerged and became visible in more than half of the male Otton frogs. Presumably, those with a visible spine might have used them recently in combat, whereas those that were not visible had not been used recently (at least for more than the period during which the wound healed). Piercing of the skin while using spines or claws has been observed in other frog species (Blackburn, Hanken & Jenkins, 2008) and in salamanders (Brodie,

Nussbaum & DiGiovanni, 1984). Blackburn et al. (2008) showed that the claws of Astylosternus and Trichobatrachus pierce their way to functionality, and Brodie et al. (1984) showed that Echinotriton andersoni has sharp ribs that protrude through the body wall against predators. Blackburn et al. (2008, p. 356) stated MCE公司 that the bony ribs of E. andersoni are the only comparative structures to the claws of Astylosternus and Trichobatrachus, and that the claws were not analogous to the prepollical spines of five-fingered frog species as ‘the spines … appear to grow through the skin rather than traumatically pierce it’. However, the spines of Otton frogs do not grow through the skin, but rather pierce the sheath traumatically. Thus, the claws of Astylosternus and Trichobatrachus, the ribs of E. andersoni and the prepollical spines of Otton frogs might have some common developmental features. Although amphibians are known

to have remarkable regenerative capacity (Brockes & Kumar, 2005), a structure that damages the animal itself in its use does not seem adaptive. This topic needs to be examined further and will be an interesting case study for the development of self-damaging structures. Although females do not appear to use their pseudothumbs and spines, they are still present, and a few individuals had spines that projected slightly from the sheath or showed a weak jabbing response. This could be because formation of the pseudothumb is linked developmentally with other important traits. The fact that the development of pseudothumbs in Otton frogs occurs at a fairly early stage, even in larvae (Tokita & Iwai, 2010), supports this idea. Corresponding formation of spines in females was also observed in some adult females of H.

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