Genetic Variation in Antimicrobial Activity of Honey Bee (Apis mellifera) Seminal Fluid

Abstract

Honey bees can host a remarkably large number of different parasites and pathogens, and some are known drivers of recent declines in wild and managed bee populations. Here, we studied the interactions between the fungal pathogen Nosema apis and seminal fluid of the Western honey bee (Apis mellifera). Honey bee seminal fluid contains multiple antimicrobial molecules that kill N. apis spores and we therefore hypothesized that antimicrobial activities of seminal fluid are genetically driven by interactions between honey bee genotype and different N. apis strains/ecotypes, with the virulence of a strain depending on the genotype of their honey bee hosts. Among the antimicrobials, chitinases have been found in honey bee seminal fluid and have the predicted N. apis killing capabilities. We measured chitinase activity in the seminal fluid of eight different colonies. Our results indicate that multiple chitinases are present in seminal fluid, with activity significantly differing between genotypes. We therefore pooled equal numbers of N. apis spores from eight different colonies and exposed subsamples to seminal fluid samples from each of the colonies. We infected males from each colony with seminal fluid exposed spore samples and quantified N. apis infections after 6 days. We found that host colony had a stronger effect compared to seminal fluid treatment, and significantly affected host mortality, infection intensity and parasite prevalence. We also found a significant effect of treatment, as well as a treatment × colony interaction when our data were analyzed ignoring cage as a blocking factor. Our findings provide evidence that N. apis-honey bee interactions are driven by genotypic effects, which could be used in the future for breeding purposes of disease resistant or tolerant honey bee stock.

Protecting pollinators and our food supply: understanding and managing threats to pollinator health

“…A variety of pests and pathogens can negatively impact honey bee health resulting in colony losses; however, honey bees may combat various threats through innate immune responses (Fang et al 2022;Holt et al 2021). To better understand honey bee immune responses, Baer examined the horizontal transmission of the fungal pathogen Nosema between drones and queens.…”

Long‐term sperm storage in eusocial Hymenoptera

“…However, seminal fluid can reduce N. apis spore viability by over 80% via at least two mechanisms: ( i ) the fluid's protein fraction induces extracellular germination, which disrupts the pathogen's life cycle and ( ii ) the fluid's non‐protein fraction directly reduces the viability of intact spores (Peng et al ., 2015 a ). Chitinase plays a major role in neutralizing N. apis spores (Holt et al ., 2021). Additionally, in the black garden ant ( L. niger ), the spermathecal content of virgin queens displays marked antibacterial activity against the bacterium Escherichia coli , but the degree of activity declines in strength after mating (Dávila et al ., 2018).…”