Dissertation Research: Sex Allocation and Reproductive Success in a Perennial Hermaphrodite, Solanum carolinense

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9411513 Meagher Ecological theories have predicted that the size or number of flowers on a plant should have a large effect upon the resulting reproductive success of that plant, particularly in terms of pollen spread, so that a plant with more or larger flowers will increase its reproductive success as a male parent. On the other hand, a plant has a limited resource pool which must be allocated not only to attracting pollinators, but also to filling fruit (a component of female reproductive success), growth, storage, and survival. This leads to a basic conflict within a plant. Synthesis of these two ideas--reproductive success gained through each gender and allocation-level-conflicts--has been hampered in hermaphroditic plants by problems associated with determining gender-specific fitness and assigning specific characters, such as corolla (petal) size, to either male or female success. This study will integrate allocation and fitness-component approaches to identify the precise role of different floral characters in reproductive success. The proposed research will determine resource allocation to gender functions in the perennial plant Solanum carolinense, and relate allocation patterns to realized fitness through both male and female functions. Experimental populations of S. carolinense have been planted, within which individual fruit and seed set over two growing seasons (female fitness) and male paternity (determined through genetic analysis) will be related to individual variation in the size and number of flowers. This study will therefore provide insight into the effect of resource allocation on the fitness gained through each gender in a hermaphroditic plant, and into the interrelationships of allocation and fitness between genders. In addition, controlled crosses will be performed between plants to determine the heritability of floral characters, so as to ascertain the potential for evolution of allocation regime. If flower size is environ mentally determined (for example, if larger flower parts are found on individuals growing in areas of slightly higher nutrient concentrations), any difference in reproductive ability due to allocation regime will not be passed on to offspring, and flower size and its relation to reproductive success is a random effect. In addition to contributions to basic understanding of plant reproductive success, this project will also have potential applied significance. The study species for this project, Solanum carolinense, was named one of the ten worst pasture weeds in 1980, due to the presence of toxic alkaloids, prickles, and thick persistent roots which aid in clonal spread of individual plants. It is therefore a commercially important species. Understanding allocation tradeoffs in this weed could contribute to control efforts currently practiced by farmers. In addition, the specific questions addressed concerning tradeoffs have direct applications to food plant breeding efforts, in that the results will help to explain cultivar variation in fruit production as a function of variation in floral allocation.