Dissecting yeast-dependent population differentiation and spatial segregation in Drosophila melanogaster

Adaptation to different food resources is a major mechanism shaping local adaptation and speciation. Numerous cases of food-mediated speciation are seen in plant-feeding insects. In this thesis, we first formulate seven key questions using insect literature to explore the processes of food-mediated speciation. We then experimentally investigate two critical questions regarding food-mediated population differentiation and assortative mating using the model organism Drosophila melanogaster and its essential food resource – yeast. We quantified how different fly strains respond to different yeast species, across multiple yeast-dependent life history traits. We found that fly strains respond differently to different yeast species and different life-history traits are maximized on different yeast species. This suggests that the inconsistency of responses between life-history traits forms a possible limitation to population differentiation. Additionally, we built a system for automated tracking of the mating location of flies in environments containing heterogeneous food patches to dissect food-mediated assortative mating. We discovered that flies generally mate on patches containing yeast and fly pairs exert preferences for mating on certain yeast species over others. Notably, the preference of mating on yeast depends on variables including the presence of multiple yeast species and timing of (re)mating with respect to light cycle. This suggests that some level of assortative mating may result from the preference for mating on food resources, but the strength of such assortative mating may vary with environmental conditions. Together, we present the seven-question framework for understanding food-mediated speciation and demonstrate the constraints of food-mediated population differentiation and assortative mating.