Deformed wing virus in the Western Honey Bee (Apis mellifera) : Genotypic and Phenotypic Variation Across Contexts and Scales
Restricted (Penn State Only)
- Author:
- Ray, Allyson
- Graduate Program:
- Molecular, Cellular, and Integrative Biosciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 05, 2022
- Committee Members:
- David Kennedy, Outside Field Member
Moriah Szpara, Outside Unit & Field Member
Elizabeth Mcgraw, Major Field Member
Christina Grozinger, Co-Chair & Dissertation Advisor
Jason Rasgon, Co-Chair & Dissertation Advisor
Melissa Rolls, Program Head/Chair - Keywords:
- deformed wing virus
Varroa destructor
Apis mellifera
epidemiology
virus evolution
experimental evolution
viral variation
virulence
transcriptomics
genomics - Abstract:
- Insect population declines, particularly of critical pollinators such as the Western honey bee (Apis mellifera), have been reported with increasing frequency in the past decades. Numerous factors have been attributed to overall declining bee health, with viral disease identified as a key stressor in honey bee colonies across the globe. Our understanding of honey bee viral disease ecology has rapidly expanded in recent years, yet many of our conclusions are based on correlative studies, and many knowledge gaps remain regarding the diversity, molecular dynamics, and evolution of bee viruses. Thus, a mechanistic understanding of complex host-pathogen dynamics is needed to guide management and policies that support vulnerable pollinator species. In this dissertation, I conducted multi-level analyses of current topics in bee health to characterize novel viruses, explore deformed wing virus (DWV) genotype and evolution in natural and experimental settings, and broaden our understanding of the honey bee immune response. In Chapter 1, I review the current field, and identify knowledge gaps in honey bee virology and host-pathogen dynamics. I designed primers specific to newly-identified viral sequences described by our research group, and in Chapter 2, assessed for frequency and distribution of these potential pathogens in archived samples from the USDA National Honey Bee Disease Survey, assessing at both the apiary and statewide level. In Chapters 3 through 5, I used molecular techniques and experimental manipulations to better understand critical factors shaping the ongoing DWV pandemic. In Chapter 3, I utilized experimental viral passaging protocols to assess how novel vector transmission by the introduced Varroa destructor mite may impose selection pressures on DWV populations. In Chapter 4, I explored the hypothesis of adaptive viral avirulence in an isolated, mite-surviving honey bee population, examining the presence, genotype, and infection phenotype of DWV isolated from wild-caught bees within the Arnot Forest compared to bees from managed colonies. In Chapter 5, I used transcriptomic sequencing and bioinformatic approaches to test for honey bee immune responses specific to different DWV genotypes. Finally, in Chapter 6, I summarize the results of this dissertation, integrate these findings into our current understanding of honey bee disease ecology, and identify future research directions. My thesis research has provided novel insights into the complexity of honey bee disease ecology. I demonstrated that previously uncharacterized and unrecognized viruses are found broadly in apiaries across the US, meriting their further characterization and assessment of their impact on colony health. Furthermore, I demonstrated that transmission route can affect DWV genotypic diversity, and that DWV genotype can in turn shape the honey bee immune response and drive disease outcomes. These findings highlight the importance of genotyping DWV at the whole-genome nucleotide level, and identify targets for functional characterization of the honey bee molecular response to infection, particularly non-canonical immune genes within the glycolysis pathway. Ultimately, through molecular investigations of honey bee-virus interactions, we can reveal the fundamental molecular and evolutionary dynamics between hosts and pathogens and use this knowledge to support vulnerable species of bees and beyond.