Submitted to: Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2005
Publication Date: 10/1/2005
Citation: Evans, J.D., Pettis, J.S. 2005. Colony-level impacts of immune responsiveness in honeybees, Apis mellifera. Evolution. 59(10):2270-2274. Interpretive Summary: While honey bees face many threats, the most important disease is American foulbrood (AFB), caused by a bacteria. In an isolated apiary, we exposed bee colonies to AFB spores, then measured disease levels in these colonies throughout the season and collected individual bees to measure their individual immunity to AFB. Bees from colonies with lower disease levels tended to have stronger immune responses. This study suggests that immune responses can reduce disease levels in bees and that selecting for bees with 'built-in' disease resistance can be useful. The results should help bee breeders improve their stock, reducing the need for antibiotics and other controls for this important disease.
Technical Abstract: Social insects combat disease using both behavioral and physiological mechanisms. Among the physiological mechanisms, the innate immune response has great potential to both reduce individual mortality and slow the spread of pathogens among colony members. We exposed field honey bee (Apis mellifera) colonies to infectious spores of a key natural bacterial pathogen, Paenibacillus larvae. We measured colony-level disease symptoms then scored larval bees from each colony for immune responsiveness and growth rates of the bacterial pathogen, using transcript levels for at the gene encoding a key antibacterial peptide, and genes regulating bacterial development, respectively. Bees collected from colonies where colony-level disease was low had both higher immune-related transcripts and lower expression of pathogen genes, suggesting that individual immune responses by bees can reduce the colony disease level. The results reveal considerable variation across colonies in an immune trait important for survival, and we discuss alternate hypotheses for the maintenance of this variation