Adam Stow, Dave Briscoe, and Andrew Beattie. Biology, Macquarie University, Sydney, Australia
Insect societies provide ideal conditions for the spread of contagious disease. We used allodapine bees to test our prediction that sociality, high relatedness and concomitant disease susceptibility will drive the evolution antimicrobials. Candidate bee species, ranging from solitary to eusocial, were sampled from several locations in south eastern Australia. Species include solitary bees from the genus Amegilla, ‘semi-social’ bees of the genus Exoneura and eusocial bees of the genus Trigona. We collected data to look for associations between group size and / or relatedness with antimicrobial strength. Pairwise relatedness was estimated for each of our species using microsatellite loci. In all our nest-dwelling species strong relatedness structuring among nests was apparent at small geographic scales, and among species, average relatedness within nests ranged from 0.309 to 0.680. The effectiveness of antimicrobials against the microbes present in the native environment of each bee species was inferred by estimates of fungal and bacterial diversity washed from bee surfaces. Molecular-based approaches involving DNA sequence analysis at bacterial16sRNA and fungal ITS were used to estimate microbial diversity. Antimicrobials washed from the surfaces of bees were also directly tested against selected microbes. Our assays generated concentration-growth response curves from which we estimated the minimum concentration of antimicrobial that completely inhibits microbial growth. Associations between relatedness, group size and antimicrobial activity were apparent from antimicrobial concentration-growth curves and from levels of observed microbial diversity on bees of varying social structures.
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