Date of Award
8-2024
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Biological Sciences
Committee Chair/Advisor
Matthew Koski
Committee Member
Sruthi Narayanan
Committee Member
Richard Blob
Committee Member
Michael Sears
Abstract
Variegated leaves with disjointed, patterned coloration of the leaf blade are often hypothesized to have decreased photosynthetic capacity in comparison to uniformly colored leaves. Yet, many forest understory plants in tropical, subtropical, and temperate climates possess leaf variegation. Moreover, mixed findings from previous research on the physiological impacts of leaf variegation suggest variegation is adaptative under certain environmental conditions despite decreased photosynthetic tissue area. I take an eco-physiological approach to investigate agents of selection maintaining a leaf variegation polymorphism in Hexastylis, which has both quantitative and qualitative variation in variegation. First, I conduct field surveys of morph frequencies, quantitative variation in variegation, and herbivory rates across 21 populations and relate these to long-term climatic data to uncover spatial gradients of putative ecological correlates of variegation. Following the field study, I conduct an experiment to explore the adaptive physiological mechanisms underlying an elevational cline in leaf variegation. Finally, I use comparative histology, chlorophyll concentration quantification, and photosynthetic efficiency estimations to ascertain if the presence of leaf variegation should result in differential physiological performance under certain environmental conditions. I discovered an elevational cline in leaf variegation strongly correlated with climate and soil environmental gradients but not variation in herbivore pressure. Growth chamber experimentation yielded mixed results on whether leaf variegation is a physiological adaptation to the warmer temperatures and drier soil conditions of low-elevation environments. Specifically, I found evidence that higher variegation intensity at low elevations may be locally adaptive, but variegated leaves tended to outperform uniformly green leaves in most environmental conditions. The discovery of both structural and pigment variegation mechanisms in Hexastylis and increased photosynthetic capacities in pale and dark green variegated tissues further supports my hypothesis that variegation is a physiological adaptation to warmer temperatures and drier soil environments at greater risk of photoinhibition. This thesis progresses research on leaf variegation beyond strictly physiological approaches to eco-physiological approaches by incorporating the exploration of ecological factors maintaining leaf variegation across environmental gradients in nature.
Recommended Citation
Sullivan, Cierra N., "Investigating the Adaptive Potential of Leaf Variegation in Two Dimorphic Hexastylis Species" (2024). All Dissertations. 3716.
https://open.clemson.edu/all_dissertations/3716
Author ORCID Identifier
0000-0001-7316-1663