A reversal in sensory processing accompanies ongoing ecological divergence and speciation in Rhagoletis pomonella

Changes in behavior often drive rapid adaptive evolution and speciation. However, the mechanistic basis for behavioral shifts is largely unknown. The tephritid fruit fly Rhagoletis pomonella is an example of ecological specialization and speciation in action via a recent host plant shift from hawthorn to apple. These flies primarily utilize specific odors to locate fruit, and because they mate only on or near host fruit, changes in odor preference for apples versus hawthorns translate directly to prezygotic reproductive isolation, initiating speciation. Using a variety of techniques, we found a reversal between apple and hawthorn flies in the sensory processing of key odors associated with host fruit preference at the first olfactory synapse, linking changes in the antennal lobe of the brain with ongoing ecological divergence. Indeed, changes to specific neural pathways of any sensory modality may be a broad mechanism for changes in animal behavior, catalyzing the genesis of new biodiversity.