Evolution of Senecio and Lobelia in the East African Mountains

东非的山脉为研究进化事件的模式和速度提供了一个独特的机会。这些山脉数量众多、高大而又孤立，考虑到植被的高度分带，它们形成了一个分层的生境-岛屿系统，可以进行数学分析，并提出关于植物适应性辐射的可检验的预测。巨大的塞内西奥（塞内西奥）。杉木和巨型半边莲（半边莲科，Rhynchopetalum）经历了足够的地理和海拔辐射（导致许多地方性和趋同进化），可以评估和比较它们对山地系统物理特征的进化反应。这些植物还显示出与巨型莲座生命形式相关的几个不寻常的形态学特征，即：(1)每天开放和关闭巨大的顶叶莲座，(2)保留老的、死的叶子的绝缘外壳，(3)极大地扩大了髓体积，提供了一个内部储水器，(4)多糖的分泌影响半边莲莲座叶和空心花序冻结水分的特性。帕尔默博士和诺克斯先生的研究目的是重建这两个群体的进化史。基于叶绿体和核糖体DNA限制位点变异的系统发育假说将用于测试从山地系统的数学分析中得出的预测，并解释适应形态的模式。这项研究将深入了解地理辐射与海拔辐射的频率，迁徙与远距离分散的相对重要性，进化趋同的程度，进化分化的速度，以及几个特别感兴趣的分类学问题。如果Senecio或Lobelia的地理辐射模式与火山形成的顺序相对应，那么既定的地质年代学可能为评估分子钟的运作提供独立的证据。

The mountains of East Africa provide a unique opportunity to study the mode and tempo of evolutionary events. The mountains are sufficiently numerous, tall and isolated that, given the altitudinal zonation of vegetation, they form a stratified system of habitat-islands which is amenable to mathematical analysis and the formulation of testable predictions concerning the adaptive radiation of plants. The giant senecios (Senecio ser. Arborei) and the giant lobelias (Lobelia sect. Rhynchopetalum) have undergone sufficient geographic and altitudinal radiation (resulting in much endemism and convergent evolution) to allow assessment and comparison of their evolutionary responses to the physical characteristics of the mountain system. These plants also display several unusual morphological features associated with the giant-rosette life-form, namely (1) daily opening and closing of the massive terminal leaf-rosettes, (2) retention of an insulating jacket of old, dead leaves, (3) greatly enlarged pith volume which provides an internal reservoir of water, and (4) secretion of polysaccharides that affect the freezing characteristics of water impounded by the leaf-rosettes and the hollow inflorescences of Lobelia. The purpose of research by Dr. Palmer and Mr. Knox is to reconstruct the evolutionary histories of these two groups. Phylogenetic hypotheses based on restriction-site variation in chloroplast and nuclear ribosomal DNA will be used to test the predictions derived from mathematical analysis of the mountain system and to interpret the patterns in adaptive morphology. This research will provide insight into the frequency of geographic versus altitudinal radiation, the relative importance of migration versus long-distance dispersal, the extent of evolutionary convergence, the rate of evolutionary divergence, and several points of particular taxonomic interest. If the pattern of geographic radiation for Senecio or Lobelia corresponds to the sequence of volcanic mountain formation, then the established geochronology may provide an independent line of evidence for evaluating the operation of a molecular clock.