Genetic Variation in Taste Sensitivity to Sugars in Drosophila melanogaster

Taste sensitivity plays a major role in controlling feeding behavior, and alterations in feeding habit induced by changes in taste sensitivity can drive speciation. We investigated variability in taste preferences in wild-derived inbred lines from the Drosophila melanogaster Genetic Reference Panel. Preferences for different sugars, which are essential nutrients for fruit flies, were assessed using two-choice preference tests that paired glucose with fructose, sucrose, or trehalose. The two-choice tests revealed that individual lines have differential and widely variable sugar preferences, and that sugar taste sensitivity is polygenic in the inbred population tested. We focused on 2 strains that exhibited opposing preferences for glucose and fructose, and performed proboscis extension reflex tests and electrophysiological recordings on taste sensilla upon exposure to fructose and glucose. The results indicated that taste sensitivity to fructose is dimorphic between the 2 lines. Genetic analysis showed that high sensitivity to fructose is autosomal dominant over low sensitivity, and that multiple loci on chromosomes 2 and 3 influence sensitivity. Further genetic complementation tests for fructose sensitivity on putative gustatory receptor (Gr) genes for sugars suggested that the Gr64a-Gr64f locus, not the fructose receptor gene Gr43a, might contribute to the dimorphic sensitivity to fructose between the 2 lines.