Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (5 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2023)

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.

    • Article
    • Peer Reviewed
    UC Riverside Previously Published Works (2023)
    High concentrations of dietary salt are harmful to health. Like most animals, Drosophila melanogaster are attracted to foods that have low concentrations of salt, but show strong taste avoidance of high salt foods. Salt in known on multiple classes of taste neurons, activating Gr64f sweet-sensing neurons that drive food acceptance and 2 others (Gr66a bitter and Ppk23 high salt) that drive food rejection. Here we find that NaCl elicits a bimodal dose-dependent response in Gr64f taste neurons, which show high activity with low salt and depressed activity with high salt. High salt also inhibits the sugar response of Gr64f neurons, and this action is independent of the neurons taste response to salt. Consistent with the electrophysiological analysis, feeding suppression in the presence of salt correlates with inhibition of Gr64f neuron activity, and remains if high salt taste neurons are genetically silenced. Other salts such as Na2SO4, KCl, MgSO4, CaCl2, and FeCl3 act on sugar response and feeding behavior in the same way. A comparison of the effects of various salts suggests that inhibition is dictated by the cationic moiety rather than the anionic component of the salt. Notably, high salt-dependent inhibition is not observed in Gr66a neurons-response to a canonical bitter tastant, denatonium, is not altered by high salt. Overall, this study characterizes a mechanism in appetitive Gr64f neurons that can deter ingestion of potentially harmful salts.
      Cover page: An inhibitory mechanism for suppressing high salt intake in Drosophila.
      • Article
      • Peer Reviewed
      UC Riverside Previously Published Works (2023)
      Comparative studies of related but ecologically distinct species can reveal how the nervous system evolves to drive behaviors that are particularly suited to certain environments. Drosophila melanogaster is a generalist that feeds and oviposits on most overripe fruits. A sibling species, D. sechellia, is an obligate specialist of Morinda citrifolia (noni) fruit, which is rich in fatty acids (FAs). To understand evolution of noni taste preference, we characterized behavioral and cellular responses to noni-associated FAs in three related drosophilids. We find that mixtures of sugar and noni FAs evoke strong aversion in the generalist species but not in D. sechellia. Surveys of taste sensory responses reveal noni FA- and species-specific differences in at least two mechanisms-bitter neuron activation and sweet neuron inhibition-that correlate with shifts in noni preference. Chemoreceptor mutant analysis in D. melanogaster predicts that multiple genetic changes account for evolution of gustatory preference in D. sechellia.
        Cover page: Evolution of fatty acid taste in drosophilids.
        • Article
        • Peer Reviewed
        UC Riverside Previously Published Works (2021)
        Chemosensory systems are critical for evaluating the caloric value and potential toxicity of food. While animals can discriminate between thousands of odors, much less is known about the discriminative capabilities of taste systems. Fats and sugars represent calorically potent and attractive food sources that contribute to hedonic feeding. Despite the differences in nutritional value between fats and sugars, the ability of the taste system to discriminate between different rewarding tastants is thought to be limited. In Drosophila, taste neurons expressing the ionotropic receptor 56d (IR56d) are required for reflexive behavioral responses to the medium-chain fatty acid, hexanoic acid. Here, we tested whether flies can discriminate between different classes of fatty acids using an aversive memory assay. Our results indicate that flies are able to discriminate medium-chain fatty acids from both short- and long-chain fatty acids, but not from other medium-chain fatty acids. While IR56d neurons are broadly responsive to short-, medium-, and long-chain fatty acids, genetic deletion of IR56d selectively disrupts response to medium-chain fatty acids. Further, IR56d+ GR64f+ neurons are necessary for proboscis extension response (PER) to medium-chain fatty acids, but both IR56d and GR64f neurons are dispensable for PER to short- and long-chain fatty acids, indicating the involvement of one or more other classes of neurons. Together, these findings reveal that IR56d is selectively required for medium-chain fatty acid taste, and discrimination of fatty acids occurs through differential receptor activation in shared populations of neurons. Our study uncovers a capacity for the taste system to encode tastant identity within a taste category.
          • Article
          • Peer Reviewed
          UC Riverside Previously Published Works (2021)
          Food choice, in animals, has been known to change with internal nutritional state and also with variable dietary conditions. To better characterize mechanisms of diet-induced plasticity of food preference in Drosophila melanogaster, we synthesized diets with macronutrient imbalances and examined how food choice and taste sensitivity were modified in flies that fed on these diets. We found that dietary macronutrient imbalances caused compensatory behavioral shifts in both sexes to increase preference for the macronutrient that was scant in the food source, and simultaneously reduce preference for the macronutrient that was enriched. Further analysis with females revealed analogous changes in sweet taste responses in labellar neurons, with increased sensitivity on sugar-reduced diet and decreased sensitivity on sugar-enriched diet. Interestingly, we found differences in the onset of changes in taste sensitivity and behavior, which occur over 1-4 d, in response to dietary sugar reduction or enrichment. To investigate molecular mechanisms responsible for diet-induced taste modulation, we used candidate gene and transcriptome analyses. Our results indicate that signaling via Dop2R is involved in increasing cellular and behavioral sensitivity to sugar as well as in decreasing behavioral sensitivity to amino acids on dietary sugar reduction. On the other hand, cellular and behavioral sensitivity to sugar relies on dilp5 and a decrease in sugar preference following dietary sugar abundance was correlated with downregulation of dilp5 Together, our results suggest that feeding preference for sugar and amino acid can be modulated independently to facilitate food choice that accounts for prior dietary experience.SIGNIFICANCE STATEMENT Animals adjust their feeding preferences based on prior dietary experiences. Here, we find that upon dietary macronutrient deprivation, flies undergo compensatory changes in food preference. The altered preference correlates with changes in peripheral taste sensitivity. While Dop2R mediates changes following dietary sugar reduction, downregulation of dilp5 is associated with changes caused by a sugar-enriched diet. This study contributes to a better understanding of neurophysiological plasticity of the taste system in flies, and its role in facilitating adjustment of foraging behavior based on nutritional requirements.
            Top