Department of Geology, The Field Museum, 1400 South Lake Shore Drive, Chicago, Illinois 60605, USA.
Evolution. 2011 Feb;65(2):377-94. doi: 10.1111/j.1558-5646.2010.01118.x. Epub 2010 Oct 12.
Morphology reflects ecological pressures, phylogeny, and genetic and biophysical constraints. Disentangling their influence is fundamental to understanding selection and trait evolution. Here, we assess the contributions of function, phylogeny, and habitat to patterns of plastron (ventral shell) shape variation in emydine turtles. We quantify shape variation using geometric morphometrics, and determine the influence of several variables on shape using path analysis. Factors influencing plastron shape variation are similar between emydine turtles and the more inclusive Testudinoidea. We evaluate the fit of various evolutionary models to the shape data to investigate the selective landscape responsible for the observed morphological patterns. The presence of a hinge on the plastron accounts for most morphological variance, but phylogeny and habitat also correlate with shape. The distribution of shape variance across emydine phylogeny is most consistent with an evolutionary model containing two adaptive zones--one for turtles with kinetic plastra, and one for turtles with rigid plastra. Models with more complex adaptive landscapes often fit the data only as well as the null model (purely stochastic evolution). The adaptive landscape of plastron shape in Emydinae may be relatively simple because plastral kinesis imposes overriding mechanical constraints on the evolution of form.
形态反映了生态压力、系统发育和遗传及生物物理限制。解析它们的影响对于理解选择和性状进化至关重要。在这里，我们评估了功能、系统发育和生境对龟鳖目龟类腹甲（腹壳）形状变异模式的影响。我们使用几何形态测量法量化形状变化，并通过路径分析确定几个变量对形状的影响。影响腹甲形状变化的因素在龟鳖目龟类和更广泛的龟鳖目之间是相似的。我们评估了各种进化模型对形状数据的拟合程度，以研究负责观察到的形态模式的选择景观。腹甲上铰链的存在解释了大部分形态方差，但系统发育和生境也与形状相关。腹甲形状在龟鳖目系统发育中的分布与包含两个适应区的进化模型最一致，一个适应区是为具有动力学腹甲的龟类，另一个适应区是为具有刚性腹甲的龟类。具有更复杂适应景观的模型通常与数据的拟合程度与空模型（纯随机进化）一样好。龟鳖目龟类腹甲形状的适应景观可能相对简单，因为腹甲运动对形式进化施加了压倒性的机械限制。
