Calcium Taste Avoidance in Drosophila

Many animals, ranging from vinegar flies to humans, discriminate a wide range of tastants, including sugars, bitter compounds, NaCl, and sour. However, the taste of Ca2+ is poorly understood, and it is unclear whether animals such as Drosophila melanogaster are endowed with this sense. Here, we examined Ca2+ taste in Drosophila and showed that high levels of Ca2+ are aversive. The repulsion was mediated by two mechanisms-activation of a specific class of gustatory receptor neurons (GRNs), which suppresses feeding and inhibition of sugar-activated GRNs, which normally stimulates feeding. The distaste for Ca2+, and Ca2+-activated action potentials required several members of the variant ionotropic receptor (IR) family (IR25a, IR62a, and IR76b). Consistent with the Ca2+ rejection, we found that high concentrations of Ca2+ decreased survival. We conclude that gustatory detection of Ca2+ represents an additional sense of taste in Drosophila and is required for avoiding toxic levels of this mineral.