Abstract
In Drosophila, diet is considered a prominent factor shaping the associated bacterial community. However, the host population background (e.g. genotype, geographical origin and founder effects) is a factor that may also exert a significant influence and is often overlooked. To test for population background effects, we characterized the bacterial communities in larvae of six genetically differentiated and geographically distant D. melanogaster lines collected from natural populations across Europe. The diet for these six lines had been identical for ca. 50 generations, thus any differences in the composition of the microbiome originates from the host populations. We also investigated whether induced shifts in the microbiome—in this case by controlled antibiotic administration—alters the hosts’ resistance to parasitism. Our data revealed a clear signature of population background on the diversity and composition of D. melanogaster microbiome that differed across lines, even after hosts had been maintained at the same diet and laboratory conditions for over 4 years. In particular, the number of bacterial OTUs per line ranged from 8 to 39 OTUs. Each line harboured 2 to 28 unique OTUs, and OTUs that were highly abundant in some lines were entirely missing in others. Moreover, we found that the response to antibiotic treatment differed among the lines and significantly altered the host resistance to the parasitoid Asobara tabida in one of the six lines. Wolbachia, a widespread intracellular endosymbiont associated with parasitoid resistance, was lacking in this line, suggesting that other components of the Drosophila microbiome caused a change in host resistance. Collectively, our results revealed that lines that originate from different population backgrounds show significant differences in the established Drosophila microbiome, outpacing the long-term effect of diet. Perturbations on these naturally assembled microbiomes to some degree influenced the hosts’ resistance against natural parasites.
Highlights
Macro-organisms can be viewed as distinct ecosystems, in which numerous microorganisms establish close mutualist, commensal and pathogenic associations with their hosts [1]
Since the tested lines have been maintained on an identical diet for four years, our finding provides an argument against the widely accepted view that diet is the key determinant in Drosophila-microbiome system
Our data clearly shows that host population background is an important factor determining bacterial community composition
Summary
Macro-organisms can be viewed as distinct ecosystems, in which numerous microorganisms establish close mutualist, commensal and pathogenic associations with their hosts [1]. Curing Drosophila from its microbiome revealed modifications in a number of host physiological responses, ranging from reproduction [9] to immunity and resistance to parasitoids and pathogens [10,11,12,13,14,15]. Some of these changes are attributed to the genus Wolbachia, a widespread endosymbiont of arthropods [9], but Wolbachia is not the only bacterium affecting hosts’ fitness. Much research has been performed on the range of processes that are affected by the microbiome [20], it is still not clear what the relative contributions are of different mechanisms shaping the Drosophila microbiome and host-symbiont interactions
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