Chiari Ylenia, Claude Julien
Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut 06520-8106, USA.
J Morphol. 2011 Mar;272(3):379-86. doi: 10.1002/jmor.10923. Epub 2011 Jan 18.
Galápagos tortoises possess two main shell forms, domed and saddleback, that correlate with the biogeographic history of this species group. However, the lack of description of morphological shell variation within and among populations has prevented the understanding of the contribution of evolutionary forces and the potential role of ontogeny in shaping morphological shell differences. Here, we analyze two lineages of Galápagos tortoises inhabiting Santa Cruz Island by applying geometric morphometrics in combination with a photogrammetry 3D reconstruction method on a set of tortoises of different ages (from juvenile to adult). The aim of this study is to describe morphological features on the carapace that could be used for taxonomic recognition by taking into account confounding factors, such as the morphological changes occurring during growth. Our results indicate that despite the shared similarities of growth patterns and of morphological changes observed during growth, the two lineages and the different sexes can be distinguished on the basis of distinct carapace features. Lineages differ by the shape of the vertebral (especially concerning their width) and pleural scutes, with one lineage having a more compressed carapace shape, whereas the other possesses a carapace that is more elongated and expanded toward the sides as well as an higher positioning of the first vertebral scute. Furthermore, females have a more elongated and wider carapace shape than males. Finally, carapace shape changes with growth, with vertebral scutes becoming narrower and pleural scutes becoming larger during late ontogeny.
加拉帕戈斯陆龟有两种主要的壳形，圆顶形和鞍背形，这与该物种群的生物地理历史相关。然而，由于缺乏对种群内部和种群之间壳形态变化的描述，阻碍了我们对进化力量的贡献以及个体发育在塑造壳形态差异方面潜在作用的理解。在这里，我们通过对一组不同年龄（从幼年到成年）的陆龟应用几何形态计量学并结合摄影测量三维重建方法，分析了栖息在圣克鲁斯岛的两个加拉帕戈斯陆龟谱系。本研究的目的是描述背甲上的形态特征，这些特征可用于分类识别，同时考虑到诸如生长过程中发生的形态变化等混杂因素。我们的结果表明，尽管在生长过程中观察到生长模式和形态变化有共同的相似之处，但两个谱系和不同性别可以根据背甲的不同特征区分开来。谱系在椎盾（特别是其宽度）和肋盾的形状上有所不同，一个谱系的背甲形状更扁平，而另一个谱系的背甲更细长，向两侧扩展，并且第一枚椎盾的位置更高。此外，雌性的背甲形状比雄性更细长、更宽。最后，背甲形状随生长而变化，在个体发育后期，椎盾变窄，肋盾变大。
