Shubin Neil, Wake David B, Crawford Andrew J
Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania, 19104.
Museum of Vertebrate Zoology, University of California, Berkeley, California, 94720.
Evolution. 1995 Oct;49(5):874-884. doi: 10.1111/j.1558-5646.1995.tb02323.x.
Variation in the limb skeleton was studied in a large sample (452 individuals) of adult newts (Taricha granulosa) from a single population in central California. A standard morphology is found in the hands and feet in more than 70% of individuals, but there is important variation in the remainder of the sample. Although twice as many individuals express variant tarsal (18.9%) than carpal (9.3%) patterns, the carpus reveals a greater diversity of variant conditions. Only a few of the many possible arrangements (including loss, addition, and amalgamation) of the seven carpal and nine tarsal elements are encountered. Most of the observed patterns are readily classified on the basis of phylogenetic relationship and models of development. Five patterns are bilaterally symmetrical. Two of these five arrangements are atavisms that represent plesiomorphic states. The other three symmetrical variants duplicate patterns found elsewhere among derived urodele taxa. These homoplastic patterns correspond to apomorphies of other genera within the same family or apomorphies of deeply nested and highly specialized members of other families (e.g., several plethodontid genera). This variation reveals the potential of the generative system and suggests the existence of limited domains of phenotypic expression. Both the origin of novelty and the restoration of ancestral states reflect the action of design constraints that not only place limits but also provide opportunities during the morphologic and phyletic diversification of urodeles.
对来自加利福尼亚中部单一群体的大量成年粗皮渍螈（Taricha granulosa）样本（452 个个体）的四肢骨骼变异进行了研究。超过 70%的个体的手和脚呈现出标准形态，但样本的其余部分存在重要变异。虽然表现出跗骨变异模式（18.9%）的个体数量是腕骨变异模式（9.3%）个体数量的两倍，但腕骨显示出更多样的变异情况。在七种腕骨和九种跗骨元素的众多可能排列方式（包括缺失、增加和融合）中，只出现了少数几种。大多数观察到的模式很容易根据系统发育关系和发育模型进行分类。有五种模式是双侧对称的。这五种排列方式中的两种是返祖现象，代表着近祖状态。其他三种对称变异重复了在其他有尾目衍生类群中发现的模式。这些同塑性模式对应于同一科内其他属的衍征，或其他科中深度嵌套且高度特化成员的衍征（例如，几个无肺螈科属）。这种变异揭示了生成系统的潜力，并表明存在有限的表型表达域。新奇特征的起源和祖先状态的恢复都反映了设计限制的作用，这些限制不仅施加了限制，而且在有尾目动物的形态和系统发育多样化过程中提供了机会。
