Author(s): Dean Peterson,
Mentor(s): John Chaston
Institution BYU
The fruit fly Drosophila melanogaster is a model for understanding the rapid responses of organisms to their changing environments, or adaptive tracking. Our previous investigations of adaptive tracking in flies responding to seasonally varying pressures showed that the microbiota can be an agent of host genetic selection. However, this previous work only investigated fly responses over 6.5 weeks of seasonal selection. To better understand how the microbiota influences adaptive tracking in D. melanogaster we subjected flies in outdoor mesocosms to 18 weeks of selection across a full summer-to-fall season in NH, USA while inoculating their diets with microorganisms that lead to divergent host phenotypes. Fly population sizes, which estimated the bacterial influence on fly fitness, differed between bacterial treatments. Bacterial strains that maximized fly fitness in peak of summer led to the poorest fitness outcomes in the fall, and vice versa. We also compared fly life history traits between the fly treatments in their offspring, reared in the laboratory as bacteria-free flies, four times during the selection period. Differences in the bacteria-free fly phenotypes of the adapting flies showed that inoculating the flies with bacteria led to genetic differences between the flies, and that certain bacterial functions relieved seasonal selective pressure on the flies. Together, these findings provide insight into how exposure to changing environments and microbial communities can influence rapid adaptation in a model animal host.