Foster D J, Podos J, Hendry A P
Redpath Museum and Department of Biology, McGill University, Montréal, QC, CanadaDepartment of Biology and Graduate Program in Organismic and Evolutionary Biology, University of Massachusetts, Amherst, MA, USA.
J Evol Biol. 2008 Jan;21(1):263-275. doi: 10.1111/j.1420-9101.2007.01449.x. Epub 2007 Nov 15.
Beak size and shape in Darwin's finches have traditionally been quantified using a few univariate measurements (length, depth, width). Here we show the improved inferential resolution of geometric morphometric methods, as applied to three hierarchical levels: (i) among seven species on Santa Cruz Island, (ii) among different sites on Santa Cruz for a single species (Geospiza fortis), and (iii) between large and small beak size morphs of G. fortis at one site (El Garrapatero). Our results support previous studies in finding an axis of shape variation (long/shallow/pointy vs. short/deep/blunt) that separates many of the species. We also detect additional differences among species in the relative sizes and positions of the upper and lower mandibles and in curvature of the mandibles. Small-scale, but potentially relevant, shape variation was also detected among G. fortis from different sites and between sympatric beak size morphs. These results suggest that adaptation to different resources might contribute to diversification on a single island.
传统上，达尔文雀的喙大小和形状是通过一些单变量测量（长度、深度、宽度）来量化的。在这里，我们展示了几何形态测量方法在三个层次水平上应用时提高的推断分辨率：（i）在圣克鲁斯岛上的七个物种之间；（ii）对于单个物种（勇地雀）在圣克鲁斯岛的不同地点之间；（iii）在一个地点（埃尔加拉帕泰罗）的勇地雀的大喙和小喙形态之间。我们的结果支持了之前的研究，即发现了一个形状变化轴（长/浅/尖与短/深/钝），该轴将许多物种区分开来。我们还检测到不同物种在上、下颌骨的相对大小和位置以及下颌骨曲率方面的其他差异。在来自不同地点的勇地雀之间以及同域分布的喙大小形态之间也检测到了小规模但可能相关的形状变化。这些结果表明，对不同资源的适应可能有助于在单个岛屿上实现多样化。
