Figure 3. Leg mechanosensory sensilla neuron activity is necessary and sufficient for Encounter Responses.

a, The frequency of Encounter Responses measured from experiments in Figure 1 (‘Dark’), illuminated experiments (‘Light’), near-anosmic mutants (IR8a¹;IR25a²;GR63a¹,ORCO¹), auditory/proprioceptive mutants (nanchung^36a), nociceptive touch mutants (piezo^KO), and gentle touch mutants (nompC^f00914). To calculate the Frequency of Encounter Responses, we tested how often each stationary fly undergoing an Encounter moved continuously for the next half-second. N = 10 experiments for each condition (density = 0.75 flies/cm²). Reductions for nanchung and piezo mutants were not statistically significant (Extended Data Table 1). b, Single frames from a high-resolution video of an Encounter between a moving fly and a stationary fly. The schematic on the middle frame shows the percent of all observed Encounter Responses resulting from touch for each leg segment (n = 104 experiments). The Encounter Response walking trajectory elicited by touch is shown in yellow on the right-hand frame. c, Encounter Response trajectories (right) colour-coded by the appendage touched by the neighbouring fly (left). Wings (W, n = 54 experiments), Legs (R1-R3 and L1-L3, n = 21, 18, 19 and 23, 15, 17 experiments, respectively). The scale bar is 1 mm and each trajectory represents up to 0.24 s of walking. d, Touch response trajectories (right) colour-coded by which appendage was touched by a metallic disc (left). Wings (W, n = 20 experiments), Legs (R1-R3 and L1-L3, n = 20, 21, 21 and 18, 21, 20 experiments, respectively). The scale bar is 2.5 mm and each trajectory represents up to 1.5 s of walking. e, The frequency of Encounter Responses elicited by moving flies with (‘oe+’) or without (‘oe−’) cuticular hydrocarbon-secreting oenocytes (n = 11 experiments each). f, A transmitted light image, inverted fluorescence image (fluorescence in black), and summed fluorescence for a Mechanosensory Sensilla driver fly leg expressing GFP. Leg mechanosensory sensilla (‘MS’) are indicated in green. A high-resolution image of the tarsus is shown on the right. Endogenous GFP fluorescence (green) is superimposed upon a transmitted light image (magenta). The scale bars are 100 μm. g, The frequency of Encounter Responses for parental line controls (UAS-Tnt/+;+ or piezo-Gal4/+;cha3-Gal80/+), Mechanosensory Sensilla driver flies expressing an inactive tetanus toxin control (UAS-Tnt^IMP/piezo-Gal4;cha3-Gal80/+), or Mechanosensory Sensilla driver flies expressing tetanus toxin (UAS-Tnt/piezo-Gal4;cha3-Gal80/+). N = 12, 13, 15, and 15 experiments, respectively. h, Blue laser optogenetic stimulation responses of flies expressing ChR2 in mechanosensory sensilla (piezo-Gal4/+; cha3-Gal80/UAS-ChR2(T159C)) in the absence (left) or presence (right) of the essential cofactor all trans-Retinal (n = 12 flies for each condition). Each box indicates the response for a single fly (‘walk’, ‘leg shift’, or ‘none’).