Influences of herbivores and inbreeding on the maintenance of a mixed mating system in the entire-leaf morning glory, Ipomoea hederacea

When insect pollinators are limited in nature, plants are forced to self-pollinate or inbreed. Offspring produced by these incestuous matings typically results in broad, detrimental changes in plant morphology and physiology. Previous studies have found that generalist herbivores perform better when reared on inbred plants. I investigated if insect responses to inbred plants were universal by using current Plant Defense Theory. The Plant Stress Hypothesis predicts that generalist herbivores will perform better on inbred plants; whereas the Plant Vigor Hypothesis predicts that specialist herbivores will perform better on outbred plants. I found that both specialist tortoise beetles and generalist armyworms performed better when reared on outbred plants, but that aphid density increased significantly faster on inbred plants. This study suggests that feeding strategy may influence herbivore performance rather than the number of potential host plants.; In addition, I investigated inbreeding depression and selfing rate in I. hederacea to determine if inbreeding depression contributed to the maintenance of the mixed mating system in Alabama populations. Inbreeding depression differed between populations and the magnitude varied for germination, growth (as measured by above ground biomass), and reproductive potential. Selfing rate ranged from ∼4% to >80% in twelve populations tested. The high selfing rates, high levels of homozygosity and low levels of inbreeding depression suggest that inbreeding depression is not the mechanism maintaining the mixed mating system in I. hederacea.; Finally, the variation in relative abundance of two sympatric tortoise beetles was investigated to determine if water conservation contributes to survival in changing environments. Cuticular permeability (CP), percentage of total body water (%TBW), rate of water loss, and percentage of body lipid content were determined for five juvenile stages and female and male adults of two sympatric species of chrysomelid beetles. This study suggests that the relative abundance of adult tortoise beetles is affected by juvenile response to environmental water stress. This conclusion is supported by low relative abundance of golden tortoise beetle larvae in a drought year and higher abundance in two "wet" years.