Development of the pseudothumb in frogs
Development of the pseudothumb in frogs
复制标题
青蛙假拇指的发育
作者：
Masayoshi Tokita;N. Iwai
青蛙的手和脚的形态高度保守，有四个手指和五个脚趾。作为一个例外，两种日本蛙类，奥顿蛙Babina subaspera和匕首蛙Babina Holsti，在前肢上有一个独特的拇指状结构(假胸腔)，在手上总共有五个手指。为了深入了解产生这种新奇性格的发育机制，我们研究了奥顿蛙的手的形态发生。在幼体中已经建立了唯一的假胸的形态模式。令人惊讶的是，这种类似于诱导活动区域的芽状结构(例如鸟类的羽芽和海龟的甲壳脊)在幼虫体内未来前极的发育部位被检测到。相比之下，这种芽状结构在其他兰科物种的幼虫中没有发现。我们讨论了有利于青蛙这种非常不寻常的特征进化的可能情景。
Frogs have highly conserved hand and foot morphology, possessing four fingers and five toes. As an exception, two Japanese ranid frog species, the Otton frog Babina subaspera and the dagger frog Babina holsti, possess a unique thumb-like structure (the pseudothumb) in the forelimb, giving an appearance of a total of five fingers on the hand. To obtain insights into the developmental mechanisms that generate this novel character, we investigated the hand morphogenesis of the Otton frog. The unique morphological pattern of the pseudothumb was already established in juveniles. Surprisingly, the bud-like structure, which is similar to the area of inductive activity (e.g. feather buds in birds and the carapacial ridge in turtles), was detected over the site where the future prepollex develops in larvae. By contrast, this bud-like structure was not found in larvae of other ranid species. We discuss possible scenarios that would favour the evolution of this very unusual trait in frogs.