Multi-tiered analyses of honey bees that resist or succumb to parasitic mites and viruses

Authors: WEAVER, DANIEL - Genformatics, Llc; CANTAREL, BRANDI - University Of Texas Southwestern Medical Center; ELSIK, CHRISTINE - University Of Missouri; Lopez, Dawn; Evans, Jay

Submitted to: BMC Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/16/2021
Publication Date: 11/21/2021
Citation: Weaver, D., Cantarel, B.L., Elsik, C., Boncristiani, D.L., Evans, J.D. 2021. Multi-tiered analyses of honey bees that resist or succumb to parasitic mites and viruses. BMC Genomics. 22(1). https://doi.org/10.1186/s12864-021-08032-z.
DOI: https://doi.org/10.1186/s12864-021-08032-z

Interpretive Summary: Varroa mites remain the single most important disease threat for honey bees. Certain populations of honey bees have survived for over a decade without preventive mite treatments. Here we use genetic tools to assess the abilities of Texas honey bee colonies to survive Varroa presence. Honey bee colonies in this population carried relatively high mite levels yet survived year after year. Genetic markers indicated possible changes in immune responses, physiological mechanisms, and signaling. This work is compared to previous efforts aimed at identifying the pressures faced by honey bees in this face of disease, as a means of adding to the knowledge of honey bee breeding traits.

Technical Abstract: The western honey bee (Apis mellifera Linnaeus [Hymenoptera: Apidae) is susceptible to multiple pathogens. One of Varroa destructor mites, and the numerous viruses they vector to their honey bee hosts, are among the most serious threats to honey bee populations, causing mortality and morbidity to both the individual honey bee and colony, the negative effects of which convey to the pollination services provided by honey bees worldwide. Here we use a combination of targeted assays and deep RNA sequencing to determine host and microbial changes in resistant and susceptible honey bee lineages. We focus on three study sets. The first involves field sampling of sympatric western bees, some derived from resistant stock and some from stock susceptible to mites. The second experiment contrasts three colonies more deeply, two from susceptible stock from the southeastern U.S. and one from mite-resistant bee stock from Eastern Texas. Finally, to decouple the effects of mites from those of the viruses they vector, we experimentally expose honey bees to DWV in the laboratory, measuring viral growth and host responses. We find strong differences between resistant and susceptible bees in terms of both viral loads and bee gene expression. Interestingly, lineages of bees with naturally low levels of the mite-vectored Deformed wing virus, also carried lower levels of viruses not vectored by mites. By mapping gene expression results against current ontologies and other studies, we describe the impacts of mite parasitism, as well as viruses on bee health against two genetic backgrounds. We identify numerous genes and processes seen in other studies of stress and disease in honey bee colonies, though we find novel genes and new patterns of expression too. We provide evidence that honey bees surviving in the face of parasitic mites do so through their abilities to resist the presence of devastating viruses vectored by these mites. By revealing responses to viral infection and mite parasitism in different lineages, our data identify candidate proteins for the evolution of mite tolerance and virus resistance.