UC Riverside

The gustatory system in insects plays a significant role not only for sensing edible food sources but also as a first line of defense to prevent ingestion of harmful, toxic substances. Both internal factors like the previous dietary experience or external factors like presence of different cues in the diet or the specialization on a particular host affects the dietary preferences and in this study we examined some of those aspects. First, we studied how niche segregation affects the feeding preferences in different Drosophila species. We observed that Drosophila sechellia, due to their adaptation in a particular host plant showed gustatory preference to three noni fatty acids octanoic, hexanoic and decanoic are aversive for the generalist sister species to D sechellia. We also found that obp18a, Gr33a and Ir47a are necessary for the differential gustatory preferences between the generalists and specialists.The fatty acids can act as nutritive source but we observed a concentration dependent taste modality is present. At higher concentrations, the hexanoic acid is strongly aversive for the flies and it depends of bitter Gr33a mediated pathway. Our study also investigating is that of mechanisms underlying compensatory changes in food preference upon macro-nutrient deprivation of either carbohydrates or proteins. Using electrophysiological and behavioral analyses, we found that macronutrient deprivation alters both taste preference and peripheral taste sensitivity in flies. We discovered that neuropeptides like dopamine and Drosophila insulin like peptide underlie these compensatory changes. Our study also examined an alternative pathway for high concentrations of salt rejection. Salt is unique, since its behavioral valence varies with concentration – low salt is favored and high salt is rejected. Accordingly, salt broadly activates both appetitive and aversive classes of taste neurons, whose combined activities control behavioral response. Given that pure salt is known to activate sweet taste neurons, we wished to evaluate the effects of neuronal response to sucrose + salt mixture. We tested mixtures of sucrose with varying concentrations of salt and found that high salt inhibited sucrose response. Sugar neuron inhibition was independent of Ir76b function, as well as Gr66a function, as high salt detection is dependent on both.