Department of Ecology and Evolutionary Biology, University of California at Los Angeles, Los Angeles, CA 90025, USA.
Proc Biol Sci. 2010 Oct 22;277(1697):3097-104. doi: 10.1098/rspb.2010.0408. Epub 2010 May 19.
Modern whales are frequently described as an adaptive radiation spurred by either the evolution of various key innovations (such as baleen or echolocation) or ecological opportunity following the demise of archaic whales. Recent analyses of diversification rate shifts on molecular phylogenies raise doubts about this interpretation since they find no evidence of increased speciation rates during the early evolution of modern taxa. However, one of the central predictions of ecological adaptive radiation is rapid phenotypic diversification, and the tempo of phenotypic evolution has yet to be quantified in cetaceans. Using a time-calibrated molecular phylogeny of extant cetaceans and a morphological dataset on size, we find evidence that cetacean lineages partitioned size niches early in the evolutionary history of neocetes and that changes in cetacean size are consistent with shifts in dietary strategy. We conclude that the signature of adaptive radiations may be retained within morphological traits even after equilibrium diversity has been reached and high extinction or fluctuations in net diversification have erased any signature of an early burst of diversification in the structure of the phylogeny.
现代鲸鱼通常被描述为一种适应性辐射，这是由各种关键创新（如须鲸的鲸须或回声定位）的进化或古鲸类灭绝后的生态机会所推动的。最近对分子系统发育上多样化率变化的分析对这种解释提出了质疑，因为它们没有发现现代分类群早期进化过程中物种形成率增加的证据。然而，生态适应性辐射的一个中心预测是快速表型多样化，而鲸目动物的表型进化速度尚未在鲸目中进行量化。利用现存鲸类的时间校准分子系统发育和大小的形态数据集，我们发现证据表明，在新须鲸的进化历史早期，鲸类谱系就已经分化出了大小生态位，而且鲸类大小的变化与饮食策略的变化一致。我们的结论是，即使在达到平衡多样性和高灭绝或净多样化波动之后，适应性辐射的特征也可能保留在形态特征中，因为在系统发育结构中，早期的多样化爆发已经消失。
