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

本研究的目的是：1)利用叶绿体和细胞核DNA序列推断海地属植物的系统发育或一套谱系关系；2)利用扫描电镜技术记录了部分海棠属植物的花发育模式；3)在相对论时间过程的背景下比较物种间发育事件的顺序，这样就可以在不假设不同物种中出现的相似阶段代表直接比较的单位的情况下比较发育事件。然后，在系统发育的背景下，将对模式形成和器官发育的相对时间的数据进行分析，以便对发育事件时间的相对变化如何影响成熟花形的假设进行明确的测试。初步数据表明，在一个主要的海蓬亚类群中，心皮（雌花器官）的形成时间比雄蕊（雄花，产生花粉的花器官）的形成时间提前，因此心皮占据了其他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。相对时间转移的结果是围绕花的径向对称的雄蕊图案过渡到雄蕊只在花的上半部分形成的双边对称排列。这项研究将是第一个阐明在花地平面水平上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深远的，但花进化的研究影响着经济上重要的学科，如园艺学和植物育种。一个特别有潜力进一步加深我们对花的进化形式的理解的群体是石竹属（石竹科），一个大约150种的属，分布在澳大利亚、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·斯特宾斯（1974年）所提出的那样，hibertia之所以成为这样一个理想的研究对象，是因为“在这些特征上，可能没有其他被子植物属表现出如此高的差异，这些特征通常被认为是‘基本的’，通常与属或更高类别的分离有关。”

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."