Date of Award

Spring 5-23-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Advisor(s)

Segraves, Kari A.

Subject Categories

Ecology and Evolutionary Biology | Life Sciences

Abstract

Whole genome duplication is one of the most pervasive forces driving plant evolution, yet modelling efforts on the establishment of polyploid plants have shown that early generation polyploids, or "neopolyploids", should experience high extinction rates due to a population demographic disadvantage. A major gap in understanding why established polyploids are so prevalent despite theoretically high extinction rates is that we know so little about the ecological consequences of neopolyploidy. For example, by investigating how neopolyploidy affects plant ecophysiology, or functional trait variation across environments, we can understand the ecological contexts that can promote polyploid establishment. Thus, a major goal of this dissertation was to understand how neopolyploidy affects plant ecophysiology and organismal performance. The first chapter tests the hypothesis that neopolyploids are more nutrient limited by comparing growth and leaf functional trait responses of diploids, neotetraploids, and established tetraploids of Heuchera cylindrica to different levels of nutrient supply. The results support the hypothesis that neopolyploidy increases growth-liming nutrient requirements, and this pattern was consistent across multiple independent origins of neopolyploidy, suggesting that increased nutrient limitation of neopolyploids is a consistent feature of whole genome duplication. The leaf functional traits and biomass allocation patterns of neotetraploids also showed that whole genome duplication induces a shift towards a more competitive or resource-acquisitive growth strategy. Although functional traits are key components of plant performance, we also lack information on the reproductive effects of neopolyploidy. Consequently, the second chapter examines the reproductive effects of neotetraploidy in a quick-growing annual. Specifically, I investigated how neopolyploidy and nutrient supply affects lifetime fitness in Arabidopsis thaliana. Similar to the first chapter, I found evidence that neotetraploidy increased nutrient requirements in A. thaliana. Neotetraploids had greater lifetime fitness than diploids, but only in high nutrient environments, further supporting the idea that neopolyploidy causes a shift to a more competitive growth strategy. Although increased nutrient limitation is a major ecophysiological consequence of neopolyploidy, another long-hypothesized ecophysiological effect is that neopolyploidy improves tolerance to harsh abiotic environments. As such, in the third chapter I tested the hypothesis that neopolyploidy improves stress tolerance. Using diploids and synthetic neotetraploids of H. cylindrica and A. thaliana, I found that neotetraploid functional traits were less responsive to salt and drought stress than diploids, supporting the hypothesis that neopolyploidy enhances stress tolerance. As opposed to the first two chapters that found consistent effects of neopolyploidy across multiple independent origins, in this experiment I found that the effect of neopolyploidy on stress tolerance was largely dependent on the independent polyploid origin. The results from the first three chapters show that neopolyploidy can improve stress tolerance but increase nutritional needs, and one mechanistic way that polyploids can overcome increased nutrient needs is through mutualistic species interactions. Thus, the fourth chapter tests whether diploids and established tetraploids differ in colonization rates by arbuscular mycorrhizal fungi (AMF) that generally serve as nutrient-providing mutualists. From field-sampled roots, I not only found greater total colonization of AMF on tetraploids than diploids, but that tetraploids also had a greater colonization by arbuscules, the interface of nutrient exchange between the host plant and fungus. The results from chapter four support the conclusion of chapters 1 and 2, that neopolyploidy increases nutrient limitation. Taken together, the results from this dissertation show that physiological changes in neopolyploids can lead to immediate differences in performance across resource environments, and that certain environmental contexts may promote the odds of neopolyploid establishment.

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