Department of Biological Sciences, University of Idaho, Moscow, Idaho 83844, USA.
Evolution. 2010 Aug;64(8):2385-96. doi: 10.1111/j.1558-5646.2010.01025.x. Epub 2010 Apr 29.
George Gaylord Simpson famously postulated that much of life's diversity originated as adaptive radiations-more or less simultaneous divergences of numerous lines from a single ancestral adaptive type. However, identifying adaptive radiations has proven difficult due to a lack of broad-scale comparative datasets. Here, we use phylogenetic comparative data on body size and shape in a diversity of animal clades to test a key model of adaptive radiation, in which initially rapid morphological evolution is followed by relative stasis. We compared the fit of this model to both single selective peak and random walk models. We found little support for the early-burst model of adaptive radiation, whereas both other models, particularly that of selective peaks, were commonly supported. In addition, we found that the net rate of morphological evolution varied inversely with clade age. The youngest clades appear to evolve most rapidly because long-term change typically does not attain the amount of divergence predicted from rates measured over short time scales. Across our entire analysis, the dominant pattern was one of constraints shaping evolution continually through time rather than rapid evolution followed by stasis. We suggest that the classical model of adaptive radiation, where morphological evolution is initially rapid and slows through time, may be rare in comparative data.
乔治·盖洛德·辛普森曾著名地假设，生命的多样性很大程度上源于适应性辐射——从单一祖先适应性类型或多或少同时发散出许多谱系。然而，由于缺乏广泛的比较数据集，识别适应性辐射一直很困难。在这里，我们使用关于各种动物类群的体型和形状的系统发育比较数据，来检验适应性辐射的一个关键模型，该模型认为最初的快速形态进化之后是相对稳定。我们将该模型与单一选择高峰和随机漫步模型进行了比较。我们几乎没有发现适应性辐射早期爆发模型的支持，而其他两个模型，特别是选择高峰模型，通常得到支持。此外，我们发现形态进化的净速率与进化枝年龄呈反比。最年轻的进化枝似乎进化得最快，因为长期变化通常不会达到从短期尺度上测量的速率所预测的分歧程度。在我们整个分析中，主要模式是随着时间的推移，约束不断塑造进化，而不是快速进化之后是稳定。我们认为，形态进化最初迅速、随着时间的推移而减缓的经典适应性辐射模型在比较数据中可能很少见。
