Date of Award
Master of Science
Ecology and Evolutionary Biology
Joseph H. Williams
Randall L. Small, Ben M. Fitzpatrick
Self-incompatibility is thought to have played a profound role in the evolution of the angiosperms. However, there is little evidence of self-incompatibility systems in early diverging lineages of flowering plants. Illicium parviflorum, one such early-divergent angiosperm, is an evergreen perennial species endemic to central Florida, particularly within the Ocala National Forest. Although locally abundant, I. parviflorum is currently listed as endangered at the state level due to being under constant threat of habitat disturbance and over-harvesting. Notably, this species had been described as self-incompatible due to its low seed-set. However, low seed set may also be a result of strong, early inbreeding depression. Using cross-pollinations, histology, and molecular analysis, I provide conclusive evidence that I. parviflorum possesses the ability to self-fertilize, while finding no evidence of a self-incompatibility system. Furthermore, cross-pollinations of individuals within and between populations revealed heterosis, while seeds collected from self-pollinations were smaller than those collected from out-crosses, suggesting that inbreeding may be reducing fitness within populations. An analysis used to estimate parental genotypes of individuals in a population using AFLP markers identified two out of 23 plants to be the result of natural self-pollination, while the mean (+ s.e.) pollen: ovule ratio of I. parviflorum was found to be 511 + 86, a ratio consistent with a species that relies primarily, but not exclusively, on outcrossing. Pollen/ovule ratios of I. parviflorum and other small flowered Illicium are lower than their larger flowered, derived relatives, suggesting that the ancestral floral type to the Illicium lineage was self-compatible. These results support the hypothesis that early angiosperm species had the ability to self-fertilize and that self-incompatibility systems did not arise until after the origin of the bisexual flower.
Buckley, Nicholas Earl, "Mating System Biology of the Florida Native Plant: Illicium parviflorum. " Master's Thesis, University of Tennessee, 2012.