Models are developed for the evolution of outcrossing in general and the evolution of distyly in particular. Field studies of distylous Lithospermum cobrense (Boraginaceae) are reported to support and compliment theoretical work. First a method is developed to model selection against selfing which takes into account the effects of consecutive generations of selfing on loss of heterozygosity. Conditions are then derived for optimal rates of outcrossing. Intermediate rates of outcrossing are optimal under a wide range of parameter values. One assumption of this model is that seedset is not pollen-limited. I then investigate the nature of inherent constraints on whether seedset is pollen-limited or resource-limited in outcrossing animal-pollinated plants, and conclude resource limitation is likely when the per-seed cost of fruit production is greater than the per-seed cost of pollen production. The model also points to why animal-pollinated plants usually have hermaphrodite flowers. This model is followed by analyses of pathways for the evolution of self-incompatibility with two mating types such as is associated with distyly. To account for this I show it necessary to postulate a fortuitous conjunction of rare mutations, very severe selection against selfing, and/or unusual mutational effects. It is also necessary to postulate resource-limited seedset. At this point I develop models for floral differentiation of mating types, culminating in the completely distylous condition. Once self-incompatibility has evolved in plants with stigmas and anthers already spatially separated, it is possible to account for complete floral differentiation under both pollen limitation and resource limitation. Field studies of L. cobrense focus on the pattern of pollen dispersal by butterflies, the mechanism accounting for this pattern, and the extent to which this pattern leads to resource or pollen limitation of seedset. In this species and in distylous species generally, the major effect of reciprocal placement of anthers and stigmas in the two mating types is to enhance the efficiency with which pollen is transported to compatible stigmas. This enhances male fitness but for full distyly to evolve it is helpful, though not strictly necessary, for female fitness to be affected too, as under pollen limitation. Finally, I argue that sporophytically controlled multiallelic self-incompatibility may originate by pathways similar to those envisioned for distyly, and that these two kinds of breeding systems are branches with a common stem.

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This thesis is a morphological study of the megagametophyte of Cleome spinosa Jacq. from the archesporium to the mature embryo sac. The characteristic structures of the ovule of various genera of the tribe Cleomoideae, of which C. spinosa is typical, are compared with those of genera of the tribe Capparidoideae found in the literature. [...]

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Microsporogenesis, embryo sac development Including fertilization, and fruit set involving cross pollinations were studied in the highly self-fertile red raspberry (Rubus idaeus L.) cultivar Mailing Jewel and the partially male sterile United States Department of Agriculture -Oregon State University selection Ore-US 1314 from the United States Department of Agriculture-Oregon State University red raspberry breeding program. Pollen was stained with aceto-carmine to determine pollen abnormality. Anthers of different filament lengths differed in the percent of normal pollen produced in the Ore-US 1314. Percent normal pollen produced by this selection is also much less than that, produced by Mailing Jewel. Longitudinal and cross sections of the anthers of both clones were examined and no direct involvement of the tapetum was observed to be contributing to the production of abnormal microspores in either clone. Anther squashes showed that only 41.8% of the cells of Ore-US 1314 underwent normal meiosis as compared to 93% in Mailing Jewel. Lagging chromosomes at meiosis I were also observed in Ore-US 1314. Cytogenetic factors are thought to be involved in causing increased pollen abortion and thus male sterility in Ore-US 1314. Examinations of embryo sac development under open pollination showed that while Ore-US 1314 did riot have a retarded embryo sac development, it had a high percentage of degenerate embryo sacs. Degeneration is believed to be a result of pollen of poor quality, incompatible pollen, the collapse of the egg cell due to failure of pollen to fertilize it at the critical time, or the involvement of all three. The pollination experiments involved self, open, and cross-pollinations of the two clones. The results obtained from the druplet set suggest that Ore-US 1314 could be both partial and cross-incompatible. Druplet set in Ore-US 1314 when open pollinated increased above that when selfed suggesting a positive reaction to pollen mixtures. Mailing Jewel, although not self-incompatible, was found to be partially cross-incompatible with Ore-US 1314. / Land and Food Systems, Faculty of / Graduate

Four plant communities of southwestern British Columbia were studied in an attempt to answer the following related questions: (1) do communities of harsh physical environments exhibit any characteristic phytosociological features? (2) are there any correlations between environmental harshness and certain synecological properties of such communities ? (3) are species of such communities selected for reproductive specializations that tend to reduce their genetic variability? The four communities (representing three types of herbaceous or semi-shrubby vegetation) were a salt marsh, two coastal sphagnum bogs, and a subalpine meadow. In answer to the first two questions, the findings of this investigation indicate that: (a) species population structure becomes more aggregated as environmental heterogeneity and physical stress increase, and less aggregated as succession proceeds and interspecific competition increases. (b) interspecific association and correlation, both negative and positive, increase as environmental heterogeneity and competition increase. (c) levels of polyploidy within communities appear to be correlated with environmental rigor (broadly defined). (d) the most abundant species within a community are the most variable and presumably have the largest niches ; niche size and population variability decrease as interspecific competition increases. (e) within a community, ecological distinctiveness reduces interspecific competition; communities under the least stress (especially seasonal stress) have the most ecologically dissimilar1 species. (f) dominance decreases as species diversity increases, and species diversity is roughly correlated with overall environmental severity. In answer to the last question: (a) all four communities are dominated by predominantly outcrossing species; there is no major shift to self-pollination or apomixis in any of the communities. (b) an index of potential recombination was devised, embodying a number of aspects of reproductive biology, according to which there is no significant difference in potential recombination, on the average, between species of the four different communities. Plant communities and their constituent species both respond to evolutionary forces, but more or less independently, at different rates, and often in different or even opposite ways. Environmental stress has a powerful effect on the structure and function of plant communities, but in an evolutionary sense there is little difference between normal (mesic, zonal) environments and extreme or azonal environments to an individual species. Different selection pressures have been operating in salt marshes, sphagnum bogs, and subalpine meadows, but the present study indicates that, on the average, the resultant evolutionary strategies of the species of these communities are equivalent. / Science, Faculty of / Botany, Department of / Graduate

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The influence of variation in style length on pollen flow and seed set was examined in six populations of Menyanthes trifoliata in southwestern British Columbia to evaluate Ganders' hypothesis that morphological distyly increases the fecundity of a diallelic self-incompatible plant. In five populations, Menyanthes was distylous and self-incompatible. The sixth population consisted of pins and morphological homostyles (thrums with unusually long styles). In each population morph frequency, pollen frequency, the composition of stigmatic pollen loads and seed set were estimated. Results from the six populations demonstrate that the size and composition of stigmatic pollen loads fluctuates erratically during the flowering season. Pins and thrums experienced disassortative pollination, assortative pollination and random pollination at different times during the season. Homostyles were always assortatively pollinated. Among populations there was a high correlation between morph frequency (pollen frequency) and the composition of stigmatic pollen loads. However, in anisoplethic populations of Menyanthes morphological distyly seems to compensate for the rarity of one floral form, by increasing the proportion of compatible pollen received by the opposite floral form. Comparison of the composition of stigmatic pollen loads of homostyles with those of thrums revealed that the separation of stigmas and anthers in distylous flowers of Menyanthes reduces the number of incompatible pollen grains received, and the reciprocal placement of stigmas and anthers appears to increase the number of compatible pollen grains received. Seed set in the six populations of Menyanthes was always below the potential maximum. Among populations there was a high correlation between the number of compatible pollen grains received and seed set. In at least one population, pollen availability was a major factor limiting seed set, but other factors are probably influencing seed set in Menyanthes as well. Thrums set significantly more seeds per capsule than homostyles. In populations of Menyanthes, the reciprocal placement of stigmas and anthers in distylous flowers (compared to homostylous flowers) increases the amount of compatible pollen deposited on stigmas, and this increase is associated with greater fecundity. / Science, Faculty of / Botany, Department of / Graduate

Call number: LD2668 .T4 1979 A43 / Master of Science

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