Figure 4.

Synchronization of rhythms in locomotion of emerged O. bicornis via light cycles. Two representative actograms (activity signals plotted in double plots) for synchronization of locomotion rhythms of emerged bees via light cycles (LD cycles). Bee1 was subjected to a light intensity of 200–400 lux and Bee2 to a light intensity of 10–30 lux during LD cycles (LD1 and LD2). The LD cycles are followed by several days in constant conditions (DD1 and DD2) which are indicated in the right margin. Bee1 was synchronized with LD1 after 3 days. On the first day of constant darkness (DD) the activity phase of the bee (marked by two blue arrows) is at the time of the day when the previous light phase of LD1 was and here the free running rhythm of the bee also starts. This demonstrates the setting of the circadian clock by daily light cycles. Under the second LD cycle (LD2) Bee1 shifted its activity rhythm even faster to synchronize with the light cycle and the activity phase of the first day in constant conditions (marked by a second set of blue arrows) coincides with the light phase of LD2. The clock of Bee2 was also set by the light cues. Bee2 adjusted its activity to the light phase in LD1 and later in LD2 respectively. It exhibited its main activity on the first day in DD1 (marked by two blue arrows) and in DD2 (marked by a second set of blue arrows) at the time of the day at which the light phase had been in the preceding LD regime. In general, bees, which were subjected to a lower light intensity, preferred to be active close to the lights off signal and showed some activity during the early dark phase (red arrow in the right actogram). Environmental bars on top depict the light regimes in LD1 and LD2 (white: light phase; black: dark phase). The approximate time of the day at which bees were moved from storage conditions (4 °C) to experimental conditions (20 °C) (before they emerged) is marked by an asterisk in the environmental bar panel.