Dissertation Research: Evolution of Senecio and Lobelia in the East African Mountains

在杰弗里·帕尔默博士的指导下，密歇根大学的研究生埃里克·诺克斯将继续在东非实地采集半边莲属和塞内西奥属的山地“巨型莲座”植物。这些植物表现出与其巨型莲座生活形式相关的几个不寻常的形态特征：(1)巨大的顶生莲座每天开放和关闭；(2)保留旧的、枯叶的绝缘外衣；(3)髓体体积大大增大，提供内部蓄水池；(4)多糖的分泌影响莲座叶（以及半边莲空心花序）所蓄水的冻结特性。巨型半边莲和仙人莲的几个物种被认为是东非山区进化适应性辐射的一个壮观例子，在东非山区，个别物种是特定山顶的特有物种或特定海拔带的原生物种。本研究的目的是重建这两个植物类群的进化史。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解释形态变化和地理分布的模式。这项研究将提供对地理（山之间）与海拔（山内）辐射频率的深入了解，迁徙与远距离分散的相对重要性，以及适应性形态特征的进化趋同程度。如果Senecio和Lobelia的地理辐射模式与东非火山形成的已知序列相对应，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。

Under guidance from Dr. Jeffrey Palmer, graduate student Eric Knox at the University of Michigan will continue field collecting in East Africa of the montane "giant rosette" plants of the genera Lobelia and Senecio. These plants display several unusual morphological features associated with their giant- rosette life-form: (l) 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 in the hollow inflorescences of Lobelia). The several species of giant lobelias and senecios are thought to provide a spectacular example of evolutionary adaptive radiation throughout the range of East African mountains, where individual species are endemic to particular mountain tops or native to particular elevational bands. The purpose of the research is to reconstruct the evolutionary histories of these two plant groups. Phylogenetic hypotheses based upon restriction-site variation in chloroplast and nuclear ribosomal DNA will be used to interpret patterns of morphological change and of geographic distribution. This research will provide insight into the frequency of geographic (between mountains) versus elevational (within mountains) radiation, the relative importance of migration versus long- distance dispersal, and the extent of evolutionary convergence in adaptive morphological traits. If the pattern of geographic radiation for Senecio and Lobelia corresponds to the known sequence of volcanic mountain formation in East Africa, then the established geochronology may provide an independent line of evidence for evaluating the operation of a molecular clock.