Evolutionary Developmental Biology Laboratory, Zoology, School of Natural Sciences, National University of Ireland, Galway, Ireland.
Evol Dev. 2013 Sep-Oct;15(5):365-72. doi: 10.1111/ede.12044.
The venom claws of centipedes, also known as forcipules, represent an evolutionary novelty that must have arisen in the centipede stem species, as they are not found in any other myriapods. The developmental-genetic changes that are involved in the origin of novelties are of considerable interest. It has previously been shown that centipede forcipules have a unique Hox code. However, this is a combinatorial code: no single Hox gene has a forcipule-specific expression. Here, we focus on Wnt genes. Two genes of this family show forcipule-specific expression in the "model centipede" Strigamia maritima: Wnt7 and Wnt11. For Wnt7, this forcipular expression zone seems to be a new one, which has arisen in evolution subsequently to other expression zones of the same gene. However, for Wnt11, the forcipule-specific expression probably arose by reduction of a more general pattern that originally included most or all of the limbs of an ancestral myriapod. Thus the developmental-genetic basis of the evolutionary change that turned the first pair of walking legs into venom claws is complex, involving different types of change in expression pattern. This sort of complexity is likely to be the case regarding evolutionary changes in morphology in general. Whether the origins of those features that can be considered as novelties are different in terms of their developmental-genetic basis from more routine evolutionary changes remains an open question.
蜈蚣的毒爪，也被称为螯肢，代表了一种进化上的新奇事物，这种新奇事物一定是在蜈蚣的原始物种中出现的，因为在其他节肢动物中都没有发现。参与新事物起源的发育遗传变化是非常有趣的。以前已经表明，蜈蚣的螯肢具有独特的 Hox 编码。然而，这是一种组合编码：没有单个 Hox 基因具有螯肢特异性表达。在这里，我们专注于 Wnt 基因。这个家族的两个基因在“模式蜈蚣”Strigamia maritima 中表现出螯肢特异性表达：Wnt7 和 Wnt11。对于 Wnt7，这个螯肢表达区似乎是一个新的区域，它是在同一基因的其他表达区之后在进化中出现的。然而，对于 Wnt11，螯肢特异性表达可能是通过减少更普遍的模式而产生的，这种模式最初包括祖节节肢动物的大部分或所有肢体。因此，将第一对步行足转化为毒爪的进化变化的发育遗传基础是复杂的，涉及表达模式的不同类型的变化。这种复杂性很可能是一般形态进化变化的情况。那些可以被认为是新奇事物的特征的起源在其发育遗传基础上是否与更常规的进化变化不同，仍然是一个悬而未决的问题。
