Date of Award
Summer 2025
Document Type
Open Access Dissertation
Department
Biological Sciences
First Advisor
Carolyn A. Wessinger
Abstract
Shifts to different primary pollinators are often accompanied by changes in suites of floral traits. Understanding how and why these floral adaptations evolve is a central goal in evolutionary biology. Within the genus Penstemon, the transition from bee-pollinated to hummingbird-pollinated flowers is a common evolutionary pattern. These pollinator shifts have caused several closely related species to exhibit distinct pollination syndromes. One example of this evolutionary phenomenon can be seen within the sister species P. eatonii (hummingbird-pollinated) and P. laevis (bee-pollinated). These two species form several hybrid zones, in which hybrid individuals exhibit colors resembling both parental species, along with a range of novel colors.
This wide range of color variation displayed across P. x jonesii hybrid individuals provides the opportunity to understand how variation in biochemical processes influence phenotypic variation. I investigated relationships between flower reflectance spectra and pigment compositions from hundreds of Penstemon x jonesii hybrid flowers. I found that flower color in these hybrid zones is controlled by three floral pigments. I also used a partial least squares approach to determine the predictive power between floral pigments and flower color. I found that flower color can be used to predict floral pigments and, alternatively, pigment composition can be used to predict flower color with a high degree of accuracy.
I also investigated whether the red flowers of P. eatonii evolved as an adaptation to promote hummingbird pollination or to evade pollination by bees. Using hybrid flower colors, I found red was among the most detectable color to hummingbirds and the least detectable color to bees, particularly against green backgrounds. Other flower colors also appeared as highly detectable as red flowers to birds, but were more detectable to bees, suggesting P. eatonii’s red flowers evolved as a result of the bee avoidance hypothesis.
Finally, I evaluated the effect of active learning versus lecture-based instruction on student engagement and performance in an undergraduate biology course. Across units, I applied alternative teaching styles to two classes of Biological Principles II. I found that student engagement is more influenced by student interest in course material than teaching style, and that active learning had little to no improvement on student academic performance.
Rights
© 2025, Josh Thomas Edward Stevens
Recommended Citation
Stevens, J. T.(2025). Hybrid Penstemon Flowers: Colors, Pigments, and Detectability & Experimental Teaching: Evaluating the Impact of Active Learning. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/8420