Date of Award

Spring 2026

Document Type

Open Access Dissertation

Department

Biological Sciences

First Advisor

Carolyn A. Wessinger

Abstract

Adaptive radiations are characterized by the rapid evolution of novel traits making them excellent study systems to identify the genetic basis of adaptation. Floral adaptations often evolve rapidly as they are shaped by the strong selective pressures imposed by pollinators. The wildflower genus Penstemon is a recent radiation displaying a large amount of floral diversity including the repeated evolution of several floral traits. One novel floral trait displayed in Penstemon flowers is the personate morphology. Personate flowers are characterized by an upward bulge in the lower lobe of the corolla tube which seals off the floral passageway. This peculiar floral trait has evolved multiple times across angiosperms, however, the evolutionary history, ecological function, and genetic mechanisms underlying this trait were previously unknown. My dissertation aims to gain a better understanding of the morphological basis, evolutionary history, ecological function, and genetic architecture of personate flowers in Penstemon subsection Penstemon.

By developing a quantitative measure of personate-ness, I found that personate flowers in Penstemon are produced by deep pleats in the ventral petal tissue that curve this petal surface upwards. Next, I used a phylogenetic framework with whole genome re-sequencing data to reveal parallel origins of personate flowers across Penstemon subsection Penstemon species. I conducted pollinator observations in native populations of personate, tubular, and open Penstemon flowers and found that, contrary to historical hypotheses, the personate morphology does not filter bees by size. I also conducted a mating system study and found that a species displaying personate flowers, P. hirsutus (L.) Willd., was better adapted to overcome the deleterious effects of inbreeding depression than open-tubed P. smallii A. Heller. Finally, I used Quantitative Trait Loci (QTL) mapping within a genetic cross (P. hirsutus x P. smallii) to identify the genetic architecture of this novel floral form. I found that personate flowers have an oligogenic genetic architecture. More specifically, I identified two unlinked loci accounting for 50% of the variation in Penstemon’s personate flowers. I also conducted differential gene expression analyses with RNA-Seq data generated from the parents of the QTL cross to pinpoint candidate genes underlying these QTLs.

Rights

© 2026, Trinity Hope Depatie

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