Ecogeographical and Micromorphological Differentiation Between Selfing and Outcrossing Sister Species

Since their emergence during the Cretaceous period, Angiosperms, or flowering plants, have achieved incredible success on land, colonizing an extensive range of environmental conditions and creating the structure of the Earth’s ecosystems. As they have adapted to these conditions, Angiosperms diverged in their niche breadth, morphological, physiological, biochemical, and phenological traits and evolved into the plant species known today. Some of the diversification within Angiosperm species is attributed to the adaptive evolution of floral traits that facilitate cross-fertilization by attracting and rewarding animal pollinators who transport their pollen or reductions in these traits to maximize self-fertilization.

In this dissertation, I explore diversification between Angiosperm species pairs with contrasting cross- and self-fertilizing mating systems, a powerful model for analyzing evolutionary patterns. In Chapter I, I used sister species pairs within Collinsia and Tonella (Plantaginaceae) to determine whether self-fertilizing species have wider niche breadths than their cross-fertilizing counterparts. I modeled niche breadth and niche overlap using bioclimatic variables and Maxent species distribution models. Next, Chapter II explores whether this relationship holds across other Angiosperm cross- and self-fertilizing species pairs. In Chapter III, Collinsia sister species pairs were analyzed to determine if conical petal cells, a trait associated with cross-fertilization, are lost during the evolution of self-fertilization. Conical cells on the petal epidermis were examined using scanning electron microscopy (SEM) to characterize the shape and size of cells.

The results of these analyses found that self-fertilizing species tend to have greater niche breadth than their cross-fertilizing sisters. There is also evidence of a reduction or loss of conical cells is associated with self-fertilizing species and could be a trait in the “selfing syndrome”.