Fig. 1: tßhnM18 mutant flies show a reduced sugar response compared to wild type flies after 20 h of starvation.

Proboscis extension response was measured in wild type (n = 79, white) and mutant flies (n = 65, grey). A. Fraction of flies that responded to several concentrations of sucrose. Data points indicate the mean. B. For each fly, we calculated a response score corresponding to the total number of all positive responses over the seven sugar presentations. This score is depicted in boxplots representing the median (bar), the 75%- and 25%-quartiles (box) and data within 1.5 times the interquartile range (whiskers). Data outside 1.5 times the interquartile range are considered as outliers (black dots). Numbers inside the boxes indicate sample sizes. The asterisk denotes significant difference between genotypes (Wilcoxon rank sum test, p < 0.05).

Fig. 2: Change in hemolymph glucose and trehalose after starvation is smaller in tßhnM18 mutants than in wild type.

The trehalose and glucose content was measured in the hemolymph of fed and 20 h starved mutant (grey) and wild type (white) flies. A. The concentration of trehalose and glucose in hemolymph is calculated from the glucose absorbance at 540nm and shown as mean ± SEM. Numbers in bars indicate sample size. B. The glucose absorbance in starved animals was normalized to the absorbance in fed animals for each genotype. The change in absorbance after starvation is shown as mean ± SEM (Welch Two Sample t-Test, n = 12, p < 0.05).

Fig. 3: tßhnM18 mutants survive longer under starvation conditions.

Survival under starvation conditions was determined by counting dead flies in vials containing either mutants (n = 16, grey) or wild type flies (n = 16, white) every 3 h at daytimes. A. Proportion of living animals per vial is depicted over time in mean ± SEM (n = 16). B. The time point of 50% death rate (LD50) is depicted as boxplots. The asterisk indicates significant difference between genotypes (Wilcoxon rank sum test, p < 0.05). Numbers beneath boxes indicate sample size.

Fig. 4: tßh induction immediately before testing increases sucrose response in mutants.

Total number of proboscis extension responses of wild type flies (white), mutants (grey), and mutants with hsp-tßh construct (blue) represented as boxplots. A. Temperature-induced ubiquitous expression of the tßh gene increases the sucrose responsiveness when expression is induced 3 h before testing. B. Inducing tßh-expression once a day during starvation but not before the test does not rescue the mutants’ sucrose response phenotype. Small numbers within graph indicate sample sizes, small letters denote significant difference between groups (paired Wilcoxon rank sum test, p < 0.05).

Fig. 5: Effect of starvation on taste neuron sensitivity.

Electrophysiological recording from different gustatory sensilla on the labellum A. in sated and starved tßhnM18 mutants (grey) and controls (white) and B. in sated (white) and starved (grey) wild type flies. Extracellular action potentials within 1 s after stimulation onset were counted and plotted as boxplots. Numbers represent the sample size of the recorded sensilla; asterisks indicate statistical differences between groups (Wilcoxon rank sum test, p < 0.05).

Fig. 6: TA- and OA-receptor mutants are differently affected in survival and sucrose response.

Female TA or OA-receptor mutants (grey) and their respective genetic background control (white) are tested in sucrose response (A) or survival (B). A. The total number of proboscis extensions to sucrose in Octß2 and two different OAMB receptor mutants are not affected. The TA-receptor mutants TyrRf05682, TyrRII∆24, and honoka respond less to sucrose, the double mutant TyrRII-TyrR∆124 is not affected. B. The LD50 in Octβ2R∆3.22 and Octß2R∆4.3 is later. Neither of the oamb mutants shows a change in survival. TyrRf05682, honoka, and the double mutant TyrRII-TyrR∆124 survive longer. TyrRII∆29 is not affected.

Small numbers within graph indicate sample sizes, small letters or asterisks indicate significant difference between regarding receptor mutant and the control (Wilcoxon rank sum test, p < 0.05).

Fig. 7: Spatial rescues of the tßhnM18 mutant.

Total number of proboscis extensions of GAL4-controls (grey) and the same GAL4-lines expressing UAS-tßh (blue), both in tßh mutant background, illustrated as boxplots. tßh expression in mutant background could increase the sugar response when expressed using Actin-GAL4, Tdc1-GAL4, and nSyb-GAL4 but not when expressed using Tdc2-GAL4 or NP7088-GAL4. Small numbers in boxes indicate sample sizes. Asterisks denote significant difference between mutant and rescue group (Wilcoxon rank sum test, p < 0.05).

Table 1: TA- and OA-receptor mutants are differently affected in survival and sugar response.

Horizontal arrows indicate no effect. Arrows indicate significant difference to respective control and illustrate the trend of the data.