| dc.contributor.author | Li, Ping. | en_US |
| dc.date.accessioned | 2014-10-21T12:34:56Z | |
| dc.date.available | 2001 | |
| dc.date.issued | 2001 | en_US |
| dc.identifier.other | AAINQ66635 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/55762 | |
| dc.description | The mechanisms that lead to the evolution of homostyly from distyly and the differentiation of two distylous floral morphs (pin and thrum) were studied by comparing floral morphometrics of homostylous and distylous groups within and among three evolutionary lineages in Amsinckia, in both mature and developing flowers. Twenty-six floral traits were included. In the two distylous flower morphs, stamen and pistil heights and many of the ancillary traits varied as expected from their close relationship to the definition of pins and thrums. In homostyles, traits related to anther height and pistil height were intermediate between pins and thrums in all lineages; for other traits homostyles generally had the smallest values. The functional anther-stigma distance and flower size were the two key characters discriminating homostyly from distyly. Stamen insertion height on the corolla tube was the major trait discriminating the three floral morphs (pin, thrum and homostyle) in Amsinckia, while style length was the major trait discriminating the four floral morphs (pin, thrum, large homostyle, and small homostyle) within A. spectabilis. Surprisingly, stigma thickness was the single most important trait discriminating the three evolutionary lineages. | en_US |
| dc.description | Paedomorphosis through neoteny and progenesis was found to be the major developmental mechanism responsible for the evolution of homostyly from distyly within all three lineages. Nevertheless, multiple heterochronic processes were generally involved, and lineages differed in the developmental particulars, including the extent of paedomorphosis, developmental dissociation, changes of ontogenetic trajectories and involvement of some other developmental processes, such as peramorphosis by acceleration. Similar developmental mechanisms were found to cause the differentiation of pins from thrums in distyly independently in three lineages. The unique ontogenetic patterns in the large-flowered homostylous morph in the A. spectabilis lineage suggested that it may represent an intermediate morph in the evolution of homostyly from distyly. | en_US |
| dc.description | Two additional major studies are included in this thesis. First, the concept and application of heterochrony, along with heterotopy and homeosis, in plant evolutionary studies have been thoroughly reviewed. Most heterochronic changes in plant evolution involve more than one of the six classic pure heterochronic processes. Neoteny, progenesis and acceleration were more common than hypermorphosis and predisplacement. Furthermore, the phenotypic effects of changes in the timing of onset or offset can be exaggerated, suppressed or reversed by changes in rate, and vice-versa. | en_US |
| dc.description | In addition, for 36 species representing 13 angiosperm families, it was found that microsporocyte meiosis terminated at only three discrete relative times during flower development despite wide variations within and among species in absolute developmental durations. A single timing class characterized each species. The three timing classes were related to fractions based on the golden ratio. Timing class was not related to ploidy level, inflorescence architecture, pollination syndrome or mating system. These findings suggested that a single exogenous process may regulate the timing of premeiotic and postmeiotic floral development, or that one rate determines the other. They further implied that the underlying developmental processes have evolved in a limited number of ways among flowering plants. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 2001. | en_US |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | | en_US |
| dc.subject | Biology, Botany. | en_US |
| dc.title | Floral morphometrics, development and evolution of homostyly from distyly in Amsinckia (Boraginaceae). | en_US |
| dc.type | text | en_US |
| dc.contributor.degree | Ph.D. | en_US |
