Figure 2

Centroid translocation and change of direction in 3^rd instar Ddc:TNT larvae throughout the ON/OFF assay. Centroid translocation (mm) and direction change (deg) values were obtained from DIAS analyses of the same representative Ddc:TNT larvae shown in Fig. 1. A, C, UAS-TNT-G/+;Ddc-GAL4/+ (Ddc:TNT-G) larvae. B, D, UAS-TNT-VIF/+;Ddc-GAL4/+ (Ddc:TNT-VIF, control) larvae. Linear movement is defined as segments of at least 5 consecutive frames with changes in direction lower than 20 degrees. Vertical dashed lines delimit the ON/OFF transitions and horizontal dashed lines demarcate the 20 degrees threshold. In the foraging stage (65–68 h AH), light triggers bouts of pausing with little centroid translocation and sharp direction changes (higher than 20 degrees) in both Ddc:TNT-G and Ddc:TNT-VIF larvae (A and B), although the response appears to be much stronger and more frequent in Ddc:TNT-G larvae (A). Furthermore, where a pronounced photophobic response of Ddc:TNT-G larvae occurs towards the end of the light (ON) pulse, it appears to persist and finish in the dark (OFF) pulse (e.g. 2^nd ON/OFF transition in A). In contrast, during the dark (OFF) pulses both 3^rd instar foraging larvae move mostly linearly (i.e. most or all direction change values are lower than 20 degrees), displaying greater centroid translocation. In the wandering stage (91–94 h AH), Ddc:TNT-G larvae (C) respond to light. In contrast, during the ON pulses Ddc:TNT-VIF wandering larvae (D) maintain linear movement for the most part. Both Ddc:TNT-G and Ddc:TNT-VIF larvae mostly show linear locomotion during the OFF pulses, similar to what is observed during foraging stage (see also Table 1).