Figure 2. Estimating move step lengths in Drosophila larva tracks across broad scales.
(A) Examples of track processing and turn identification. Row 1, column one shows an example of the effect of the Kalman filter on raw track data; column two shows the steps and turns that would result if raw track data were analysed; column three shows the steps and turns identified following the Kalman smoothing of the raw data. Row two shows the turns executed by the larva for a short section of the track. Note that the method detects small (turn 2, (T2) and large turns (turn 1 and 3 (T1, T3)). (B) Example of normal substrate exploration (control BL / + larva) shows a similar pattern of complexity at all scales, characteristic of scale-invariant Lévy walk patterns.
Figure 2—figure supplement 1. Analysis of curved paths.
Drosophila larva sometimes exhibit curved paths within movement trajectories. (A) This shows an example of a Kalman filtered track of a control larva (BL/+ at 33°C) executing a curved path. The section highlighted in red is shown in more detail in the third panel. The second panel shows the significant turns and steps for the same animal as determined using the objective move-step estimating method (Humphries et al., 2013; Tromer et al., 2015) (see Materials and methods). Without more detailed analysis, the path as plotted in is panel implies that the method identifies small steps where they appear not to occur. However, a detailed analysis of a panel 3 section is shown in (B). This demonstrates that curved tracks are indeed generated by larvae crawling in a curve (a consistent but minor deviation in heading), but that small turns do interrupt the curve and are correctly identified by the objective move-step estimation method used.
Figure 2—figure supplement 2. Effects of Kalman filter parameter changes on an example larva track.
(A) The first 10 min of a raw, unprocessed larva track compared with (B) the same track subjected to the Kalman filter (KF) parameters used for the main analysis presented in the main paper. Note the track is smoothed with no significant effect on the pattern of the principal movement path. Broad changes in the values of (C – E) the position and velocity parameters from 1.0 to 0.05, and (F – H) the minimum covariance parameter from 2.0 to 0.1, all show no significant effects on the path pattern resolution. This supports the conclusion that the finding of truncated power-law fits to larva tracks are not artefacts of track processing using a Kalman filter (see Supplementary file 2 for statistical comparisons).
Figure 2—figure supplement 3. Effect of edge collision on search strategy.
Comparison of μ exponents of the truncated Lévy power-law best model fits to exploration patterns of control animals (BL/ + and shits/+ control larvae at 22°C and 33°C) before and after a collision with the edge of the arena. A Mann Whitney test comparing before and after collision for each genotype showed no significant difference in any case confirming that the search behaviour of the larvae remained unchanged.