Exploring the relative bitterness and toxicity of different bitter compounds using Drosophila melanogaster

Abstract

newline Bitter taste is believed to have evolved in order to avoid ingestion of toxic chemicals that may harm an organism, and it has been shown in some animals that the bitterness or aversiveness of a compound may be directly related to its degree of harmful toxic effect. However, this relation is not always clear in other groups of animals, for e.g. in insects. Hence investigation was made to study the relation between bitterness or aversiveness and toxicity using three phytochemicals caffeine, coumarin and strychnine, using the vinegar fly Drosophila melanogaster, which feeds on decaying plant matter in nature, and hence is expected to show aversion towards toxic phytochemicals. The aversiveness of the three phytochemicals tested via activation of bitter sensitive peripheral taste neurons, and their receptors are already known in Drosophila from previous work. But any systematic study that compares the aversiveness with the relative toxicity of each compound was lacking. Evidence was found for positive correlation between the degree of bitterness of a compound and the degree of toxic effect it may be having on D. melanogaster. This lends support to the idea that the perception of bitter taste in drosophilids is adaptive flies show increased aversion towards compounds that are more toxic (as these are perceived as more bitter), and less aversion towards compounds that are less toxic (less bitter). A novel nanoencapsulation technique was also tried out where the aversiveness of bitter phytochemicals could be decreased by encapsulating them in CB7 thereby flies could be induced to feed on aversive chemicals that they would otherwise avoid. This can be further utilized to introduce bitter compounds into flies via their gut, to look at the physiological effects of toxicity of such compounds. newlineKey words: Drosophila melanogaster, feeding, viability, bitter compounds, sucrose, caffeine, coumarin, strychnine, nanoencapsulation, CB7. newlinexv newline