title: Seminal fluid of honeybees contains multiple mechanisms to combat infections of the sexually transmitted pathogen Nosema apis.
abstract: The societies of ants, bees and wasps are genetically closed systems where queens only mate during a brief mating episode prior to their eusocial life and males therefore provide queens with a lifetime supply of high-quality sperm. These ejaculates also contain a number of defence proteins that have been detected in the seminal fluid but their function and efficiency have never been investigated in great detail. Here, we used the honeybee Apis mellifera and quantified whether seminal fluid is able to combat infections of the fungal pathogen Nosema apis, a widespread honeybee parasite that is also sexually transmitted. We provide the first empirical evidence that seminal fluid has a remarkable antimicrobial activity against N. apis spores and that antimicrobial seminal fluid components kill spores in multiple ways. The protein fraction of seminal fluid induces extracellular spore germination, which disrupts the life cycle of N. apis, whereas the non-protein fraction of seminal fluid induces a direct viability loss of intact spores. We conclude that males provide their ejaculates with efficient antimicrobial molecules that are able to kill N. apis spores and thereby reduce the risk of disease transmission during mating. Our findings could be of broader significance to master honeybee diseases in managed honeybee stock in the future.
authors.affiliation: Centre for Integrative Bee Research (CIBER) and ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia, Bayliss Building (M316), Crawley, Western Australia 6009, Australia.
authors.forename: Yan
authors.initials: Y
authors.lastname: Peng
authors.affiliation: Centre for Integrative Bee Research (CIBER) and ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia, Bayliss Building (M316), Crawley, Western Australia 6009, Australia.
authors.forename: Julia
authors.initials: J
authors.lastname: Grassl
authors.affiliation: Centre for Integrative Bee Research (CIBER) and ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia, Bayliss Building (M316), Crawley, Western Australia 6009, Australia.
authors.forename: A Harvey
authors.initials: AH
authors.lastname: Millar
authors.affiliation: Centre for Integrative Bee Research (CIBER) and ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia, Bayliss Building (M316), Crawley, Western Australia 6009, Australia boris.baer@uwa.edu.au.
authors.forename: Boris
authors.initials: B
authors.lastname: Baer
mesh_terms: D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D001516:Bees / Q000737:chemistry / Q000378:metabolism / Q000382:microbiology*; D054884:Host-Pathogen Interactions; D008297:Male; D016818:Nosema / Q000187:drug effects / Q000502:physiology*; D012661:Semen / Q000737:chemistry*
chemical_list: D023181:Antimicrobial Cationic Peptides
keywords: antimicrobial activity; flow cytometry; host parasite interaction; spore germination