Fig. 6. Mechanisms of sustained PN responses in D. sechellia.

a Odour pulse responses of VM5d PNs in D. melanogaster and D. sechellia following application of GABA receptor antagonists. PN responses in normal AHL saline (left) or containing 100 µM picrotoxin (PTX) + 50 µM CGP54626 (right). Time courses (mean ± SEM ΔF/F₀) and quantification of ΔF/F₀ peak to the 1st and 10th stimulation are shown. Genotypes as in Fig. 5g. b Odour pulse responses of VM5d PNs in D. melanogaster and D. sechellia following application of low doses (200 µM) of mecamylamine (nAChR antagonist) to weakly block cholinergic inputs. PN responses in normal AHL saline, mecamylamine and AHL saline wash-out are shown. Time courses (mean ± SEM ΔF/F₀) and quantification are shown. n = 7 animals each. c Odour pulse responses of D. sechellia VM5d PNs in intact (top) and right antenna-ablated (bottom) animals, which halves the OSN input. Time courses (mean ± SEM ΔF/F₀) and quantification are shown. n = 7 animals each. d Model illustrating the complementary effects of OSN sensitisation (due to receptor tuning) and reduced PN adaptation (putatively due to OSN population increases; see Discussion) on odour-evoked sensory representations. The schematised PN activities in the cartoon on the right represent the combination of both processes, which we speculate lead to more sensitive and persistent long-range olfactory attraction toward the noni host fruit by D. sechellia, but not D. melanogaster. For a–c paired t test (two-sided): ***P < 0.001, *P < 0.05, NS P > 0.05. n = 8 animals each.