Fig. 5.

Distance-independent variations in song amplitude are prevalent in the data of Coen et al. (2016). Because distance affects song amplitude but not all variation in song amplitude can be explained by distance (Coen et al., 2016), we search the data of Coen et al. (2016) for consecutive pulse trains at specified distances between male and female flies to investigate residual amplitude variation. (A) To analyse residual amplitude variation, we (1) measure pulse peaks for a distance category, (2) arrange consecutive pulse trains of a given distance interval around the pulse peak with maximal amplitude, and (3) plot the arranged peaks as heat maps that illustrate residual variation of pulse amplitude at a given distance interval. We observe residual amplitude variation in the spread of amplitudes along the vertical axis of the heat plots. In panel B, we consider distance intervals of 4 mm. There are N pulses at the specified distance ranges. The numbers of pulses are N=1376 for 0–4 mm (including both 0 mm and 4 mm), N=1420 for 4–8 mm (not including 4 mm), and N=985 for 8–12 mm (not including 8 mm). In panel C, we consider distance intervals of 2 mm. The numbers of pulses are N=1376 for 0–2 mm (including both 0 mm and 2 mm), N=1523 for 2–4 mm (not including 2 mm), N=969 for 4­–6 mm (not including 4 mm), N=789 for 6–8 mm (not including 6 mm), N=575 for 8–10 mm (not including 8 mm), and N=500 for 10–12 mm (not including 10 mm).