Dissertation Research: Evolution of Floral Pattern Formation in Hibbertia (Dilleniaceae)

这项研究的目标是：1)利用叶绿体和核DNA序列推断海棠属的系统发育或一组系谱关系；2)使用扫描电子显微镜记录选定海棠属物种的花发育模式；3)在相对论时间进程的背景下比较不同物种之间的发育事件序列，以便可以比较发育事件，而不必假设不同物种的相似出现阶段代表直接比较的单位。然后，将在系统发育的背景下分析关于器官发育的模式形成和相对时间的数据的组合，以便可以明确地检验关于发育事件的时间的相对变化如何影响成熟花形态的假说。初步数据表明，在Hibbertia的一个主要类群中，心皮(雌花器官)的发生时间相对于雄蕊(雄性的、产生花粉的花器官)的发生时间已经提前，因此心皮占据了在其他分类群中产生雄蕊的花分生组织(未分化的胚胎细胞的聚集)的下半部分的空间。相对时序偏移的结果是在花周围形成径向对称的雄蕊图案，转变为完全在花的上半部分形成的两侧对称的雄蕊排列。这项研究将是第一次在花基质水平上阐明花形态差异背后的进化过程。花形态多样性的研究是植物学研究的主要焦点之一。虽然这一领域对开花植物分类的影响是最长期和最深远的，但花进化的研究影响着重要的经济学科，如园艺学和植物育种。一个特别有潜力进一步了解花型演化的类群是木属(Dilleniaceae)，约有150种，分布于澳大利亚、新喀里多尼亚和马达加斯加。正如伟大的进化植物学家G.L.Stebbins(1974)提出的那样，Hibbertia之所以成为此类研究的理想候选者，是因为“这里可能没有其他被子植物属在那些通常被认为是‘基本’的特征上表现出如此高度的变异，并且通常与属的分离甚至更高的类别相联系。”

The goals of this study are: 1) to infer the phylogeny, or set of genealogical relationships, of Hibbertia using chloroplast and nuclear DNA sequences; 2) to document the pattern of floral development using Scanning Electron Microscopy for selected Hibbertia species; 3) compare the sequences of developmental events between species in the context of a relativistic time course, so that developmental events may be compared without the assumption that similar appearing stages in the of different species represent units for direct comparison. The combination of data on the pattern formation and relative timing of organ development will then be analyzed in a phylogenetic context, so that hypotheses of how relative changes in the timing of developmental events have affected mature floral form may be explicitly tested. Preliminary data suggests that in one major group of Hibbertia, the timing of the origination of the carpels (female floral organs) has been advanced, relative to the initiation of stamens (male, pollen-producing floral organs), so that the carpels take up space on the lower half the floral meristem (aggregation of undifferentiated, embryonic cells) that in other taxa produce stamens. The result of relative timing shift is the transition of a radially symmetric patterning of stamens around the flower, to a bilaterally symmetric arrangement of stamens formed exclusively on the top half of the flower. This study will be among the first to elucidate the evolutionary processes behind differences in floral morphology at the level of the floral groundplan.The study of floral morphological diversity stands as one of the principal foci of botanical research. While the implications of this field for flowering plant classification have been the most long-standing and far-reaching, the study of floral evolution impacts economically important disciplines such as horticulture and plant breeding. A group with particularly great potential to further our understanding of the evolution of floral form is Hibbertia (family Dilleniaceae), a genus of ca. 150 species distributed in Australia, New Caledonia, and Madagascar. What makes Hibbertia such an ideal candidate for such a study is, as put forth by the great evolutionary botanist G. L. Stebbins (1974), that "[t]here is probably no other genus of angiosperms that exhibits such a high degree of variation in those characteristics that are often regarded as 'fundamental' and are usually associated with the separation of genera or even higher categories."