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Title: Variation and heritability in immune-gene expression by diseased honey bees

item DeCanini, Laura
item Collins, Anita
item Evans, Jay

Submitted to: Journal of Heredity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2006
Publication Date: 8/16/2007
Citation: Decanini, L.I., Collins, A.M., Evans, J.D. 2007. Variation and heritability in immune-gene expression by diseased honey bees. Journal of Heredity. 98:195-201.

Interpretive Summary: American foulbrood disease (AFB) is a widespread larval disease in honey bees. We exposed larval bees from several commercial honey bee lineages to the bacterial cause of AFB, then scored these bees for both survival and their abilities to mount an immune response. A three-generation breeding scheme was used to determine whether these traits were heritable and therefore suitable for breeding. It was shown that disease resistance can be significantly improved in bees, even after a single round of mating. This paper is part of a long term project to identify genetic traits that help honey bees resist AFB. The results will help bee breeders improve their stock, reducing the need for antibiotics and other controls for this disease.

Technical Abstract: Social insects are frequent targets for pathogens and have consequently evolved diverse ways to minimize pathogen impacts, one of which is the innate immune response. A mechanistic understanding of this response can help clarify population-level variation in immunity as well as a key general feature of social insects, genetic relatedness among nest mates. A controlled mating scheme was carried out to assess the efficacy and heritability of the honey bee (Apis mellifera) immune response against a natural pathogen. Daughters (queens) from a singly-mated queen were out crossed to haploid males from a total of 26 different genetic sources. Larval offspring from these matings (n= 36 colonies, 1728 individuals), as well as offspring of field colonies (n = 125 colonies, 3696 individuals) were then challenged with a widespread bee pathogen, the gram-positive bacterium Paenibacillus larvae larvae. Following bacterial challenge, a subset of larvae was collected for gene-expression analyses while others were scored for growth and survivorship. Heritability estimates for both larval survival and expression of the gene encoding the antibacterial peptide abaecin are moderately high, ~ 0.4 and 0.3, respectively. This suggests ongoing selection, and possible frequency-dependent selection, at genes involved in the immune response. Progeny scores showed high inter- and intra-sib ship variance, indicating epistatic and/or synergistic relationships among the genes involved in the immune response. The results support current models which predict that levels of immune effectors reflect amplified differences due to minor variation found in immune-pathway members.