Evolution of taste processing shifts dietary preference

Food choice is an important driver of speciation and invasion of novel ecological niches. However, we know little about the mechanisms leading to changes in dietary preference. Here we use three closely related species, Drosophila sechellia (Dsec), Drosophila simulans and Drosophila melanogaster, to study taste circuit¹ and food choice evolution. Dsec, a host specialist, feeds exclusively on a single fruit (Morinda citrifolia; noni), whereas the other two are generalists living on diverse diets². Using quantitative feeding assays, we recapitulate the preference for noni in Dsec and detect conserved sweet but altered bitter sensitivity by means of calcium imaging in peripheral taste neurons. Noni activates bitter-sensing neurons more strongly in Dsec than in the other two species owing to a small deletion in a single gustatory receptor. Using volumetric calcium imaging in the ventral brain³, we show that instead of peripheral physiology, species-specific processing of noni and sucrose signals in sensorimotor circuits recapitulates differences in dietary preference. Our data indicate that altered food choice may not be explained by peripheral receptor changes alone but rather by modifications in how sensory information is transformed into feeding motor commands.