Semester

Summer

Date of Graduation

2020

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Biology

Committee Chair

Stephen DiFazio

Committee Member

Yong-Lak Park

Committee Member

Jonathan Cumming

Committee Member

Jennifer Hawkins

Committee Member

Gina Wimp

Abstract

Organisms, such as fungi and insects, can cause millions of acres of agricultural and forest damage, while others provide billions of dollars in ecological services such as education, aesthetic enjoyment, pollination, and gardening. Plant breeding and biotechnology can potentially help establish a balance between the proliferation of detrimental pests and attraction of beneficial insects. Variation in plant physiological and morphological characteristics are extremely important in the ability of host tissues to support many different types of organisms. When that variation is genetically heritable in a plant population, shifts in the underlying genes can have predictable consequences in structuring entire ecosystems. The field of community genetics seeks to study these interactions and identify the genes important in host plants, which will ultimately allow for the prediction of community level responses to changing conditions. The main goal of my dissertation was to identify the genetic underpinnings of host plant-biotic community organization in species belonging to the Salicaceae family, which contains many species of trees and shrubs of ecological and economic importance. To date, community genetic research has established the ability of hybrid plants to have wide-ranging heritable effects on communities and ecosystems. However, only a few publications have identified the genes underlying these relationships in pure species.

In chapter 2, I utilized a pseudo-backcross hybrid family of Populus and quantitative trait analysis (QTL) as well as genomic comparisons of the P. trichocarpa and P. deltoides parents to identify potential candidate genes mediating their relationship with several insect herbivores and fungal pathogens. I found that many gene candidates had undergone recent tandem duplication and this pattern was enriched relative to the rest of the genome in the native parent QTL intervals. Additionally, I found the hybrids were mediating interactions between pathogens leading to unique genetic associations that would not normally be observed in a single species population, which may contribute to the elevated community effects that have been previously observed in natural hybrid zones. In chapter 3, I used surveys that were conducted in multiple common gardens of a population of P. trichocarpa, genome wide association analysis (GWAS), and networks to identify genes and potential biological functions underlying arthropod community composition. I found that genes associated with individual arthropods appeared to be very functionally targeted with rare variants related to metabolite production and manipulation of tissue nutrition. Genes that associated with arthropod richness and community composition have biological functions that may allow them to more broadly target multiple groups of arthropods, such as terpenoid synthesis, RNA inhibition, and transmembrane protein activity. In chapter 4, I used visual observation and pan-traps to survey the tree species Salix nigra and explore the impact of dioecy on the assembly of floral insect communities. I found that male trees supported higher diversity of floral visitors on their catkins when compared to females due to visual cues of yellow pollen. I also identified the main cross-pollinators to be three species of Andrena bees, one of which (A. nigrae) showed a preference for female flowers and was correlated to specific VOC cues from catkins. Finally, I detected an asynchrony in catkin bloom and insect emergence in early spring that threatens not only the sexual reproduction of S. nigra trees, but also the iii survival of local A. nigrae populations. Overall, I found that the dynamic plant-pathogen-herbivore-pollinator relationships are dependent on combinations of plant genetic effects with spatial and temporal environmental variability.

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