Jockusch Elizabeth L
Museum of Vertebrate Zoology and Department of Integrative Biology, University of California, Berkeley, California, 94720.
Evolution. 1997 Dec;51(6):1966-1982. doi: 10.1111/j.1558-5646.1997.tb05118.x.
To understand the evolutionary significance of geographic variation, one must identify the factors that generate phenotypic differences among populations. I examined the causes of geographic variation in and evolutionary history of number of trunk vertebrae in slender salamanders, Batrachoseps (Caudata: Plethodontidae). Number of trunk vertebrae varies at many taxonomic levels within Batrachoseps. Parallel clines in number occur along an environmental gradient in three lineages in the Coast Ranges of California. These parallel clines may signal either adaptation or a shared phenotypically plastic response to the environmental gradient. By raising eggs from 10 populations representing four species of Batrachoseps, I demonstrated that number of trunk vertebrae can be altered by the developmental temperature; however, the degree of plasticity is insufficient to account for geographic variation. Thus, the geographic variation results largely from genetic variation. Number of trunk vertebrae covaries with body size and shape in diverse vertebrate taxa, including Batrachoseps. I hypothesize that selection for different degrees of elongation, possibly related to fossoriality, has led to the extensive evolution of number of trunk vertebrae in Batrachoseps. Analysis of intrapopulational variation revealed sexual dimorphism in both body shape and number of trunk vertebrae, but no correlation between these variables in either sex. Females are more elongate than males, a pattern that has been attributed to fecundity selection in other taxa. Patterns of covariation among different classes of vertebrae suggest that some intrapopulational variation in number results from changes in vertebral identity rather than changes in segmentation.
为了理解地理变异的进化意义，必须确定导致种群间表型差异的因素。我研究了细螈（Batrachoseps，有尾目：无肺螈科）躯干椎骨数量的地理变异原因及其进化历史。细螈属内许多分类水平上躯干椎骨数量都存在差异。在加利福尼亚海岸山脉的三个谱系中，沿着环境梯度出现了数量上的平行渐变群。这些平行渐变群可能表明是适应性变化，或者是对环境梯度的一种共同的表型可塑性反应。通过孵化代表细螈属四个物种的10个种群的卵，我证明了躯干椎骨数量可因发育温度而改变；然而，可塑性程度不足以解释地理变异。因此，地理变异主要源于遗传变异。在包括细螈在内的多种脊椎动物类群中，躯干椎骨数量与体型和形状相关。我推测，对不同程度伸长的选择，可能与穴居性有关，导致了细螈属中躯干椎骨数量的广泛进化。对种群内变异的分析揭示了体型和躯干椎骨数量上的两性异形，但两性中这些变量之间均无相关性。雌性比雄性更细长，这种模式在其他类群中归因于繁殖力选择。不同类椎骨之间的协变模式表明，数量上的一些种群内变异是由椎骨特征的变化而非分节的变化引起的。
