Figure 4.
Comparison of the angular sensitivity to a moving green light spot. (a) The change of firing rate (bin size: 5°) to the green light stimulus with respect to the preferred direction of the cells (φmax) is shown for migratory (orange) and non-migratory (blue) TL neurons. Shaded areas indicate the 25–75% quantiles. Red vertical dashed lines separate the sectors that are statistically analysed in (b). (b) The mean angular sensitivity of the neurons to the green light. The TL neurons in migratory butterflies were more sensitive around the φmax (–60° to 60° (middle); p < 0.001, Z = 4.46, Wilcoxon-rank sum test), while the non-migratory neurons were more sensitive at an angular distance of about 120° away from the φmax (−180° to −60° (left); p < 0.022, Z = −3.06; +180° to +60° (right); p < 0.001, Z = −4.42, Wilcoxon rank sum test). (c) The circular plots show the normalized angular sensitivity in relation to the position of the green light for migratory (M, n = 8) and non-migratory (N, n = 5) TL neurons. Each row shows the angular sensitivity of one TL neuron. Grey dots at the perimeter of the upper plot indicate the sun azimuth over the course of a day (with respect to south) during the migration (1 November, College Station, TX). **p < 0.01 (b); ***p < 0.001 (b). (Online version in colour.)