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

Duke University, Durham NC

Investigators

Abstract

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."