title: Genetic variation in virulence among chalkbrood strains infecting honeybees.
abstract: Ascosphaera apis causes chalkbrood in honeybees, a chronic disease that reduces the number of viable offspring in the nest. Although lethal for larvae, the disease normally has relatively low virulence at the colony level. A recent study showed that there is genetic variation for host susceptibility, but whether Ascosphaera apis strains differ in virulence is unknown. We exploited a recently modified in vitro rearing technique to infect honeybee larvae from three colonies with naturally mated queens under strictly controlled laboratory conditions, using four strains from two distinct A. apis clades. We found that both strain and colony of larval origin affected mortality rates. The strains from one clade caused 12-14% mortality while those from the other clade induced 71-92% mortality. Larvae from one colony showed significantly higher susceptibility to chalkbrood infection than larvae from the other two colonies, confirming the existence of genetic variation in susceptibility across colonies. Our results are consistent with antagonistic coevolution between a specialized fungal pathogen and its host, and suggest that beekeeping industries would benefit from more systematic monitoring of this chronic stress factor of their colonies.
authors.affiliation: Centre for Social Evolution, Faculty of Life Sciences, Department of Agriculture and Ecology, University of Copenhagen, Copenhagen, Denmark. Vojvodic.sv@gmail.com
authors.forename: Svjetlana
authors.initials: S
authors.lastname: Vojvodic
authors.forename: Annette B
authors.initials: AB
authors.lastname: Jensen
authors.forename: Bo
authors.initials: B
authors.lastname: Markussen
authors.forename: Jørgen
authors.initials: J
authors.lastname: Eilenberg
authors.forename: Jacobus J
authors.initials: JJ
authors.lastname: Boomsma
mesh_terms: D000818:Animals; D001203:Ascomycota / Q000235:genetics* / Q000472:pathogenicity; D056630:Beekeeping / Q000379:methods; D001516:Bees / Q000235:genetics* / Q000382:microbiology* / Q000502:physiology; D005260:Female; D014644:Genetic Variation; D005838:Genotype; D007814:Larva / Q000382:microbiology; D008297:Male; D008858:Microscopy, Phase-Contrast / Q000379:methods; D008954:Models, Biological; D008957:Models, Genetic; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D012306:Risk; D017422:Sequence Analysis, DNA; D013696:Temperature; D014774:Virulence