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节奏提供了一个独特的机会。这些山脉足够多、高和孤立，鉴于植被的高度地带性，它们形成了一个分层的栖息地-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测试预测。巨型千里光(Senecio Ser.Arborei)和巨型半边莲(Lobelia sec.)它们)已经经历了足够的地理和高度辐射(导致许多特有和趋同的进化)，从而能够评估和比较它们对山地系统物理特征的进化反应。这些植物还表现出与巨型莲座状生活型相关的几个不同寻常的形态特征，即(1)巨大的顶生叶莲座体的每日开合，(2)保留旧的枯叶的绝缘外壳，(3)提供内部水分的极大的髓体积，以及(4)影响半边莲叶莲座和中空花序蓄水冻结特性的多糖分泌。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被用来检验从山系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垂直辐射的频率、迁徙与远距离扩散的相对重要性、进化趋同的程度、进化分歧的速度，以及几个具有特殊分类学意义的点。如果Senecio或Lobelia的地理辐射模式与火山山形成序列相对应，那么已建立的地质年代学可能为评估分子钟的运行提供一条独立的证据线。

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.