Effects of temperature on circadian rhythm in the Japanese honeybee, Apis cerana japonica

Temperature influences key aspects of insect circadian rhythms. The locomotor rhythm in foragers of the Japanese honeybee, Apis cerana japonica, was entrained to a skeleton temperature cycle. An initial warm temperature pulse was imposed at the beginning of subjective day and a second was applied at the end of the subjective day. A single warm pulse given every early subjective day in constant darkness (DD) entrained the locomotor rhythm without a second temperature pulse, but a single pulse given in late subjective day allowed a free-running rhythm. When honeybees were kept under a light–dark cycle, their body temperatures increased by 7–8 °C with locomotor activity. This temperature elevation remained during the photophase but followed the ambient environmental temperature at night. Body temperature oscillations continued to be circadian in DD, and temperature elevation occurred during the subjective day. In DD, the free-running period τ of locomotor activity increased when the ambient temperature increased from 27 to 37 °C, although these changes were within the range of temperature compensation for many organisms. Under continuous light conditions (LL), τ remained constant with more strict temperature compensation. Patterns of brain period mRNA levels of forager bees maintained at different temperatures in LL revealed that the free-running period of per mRNA rhythm was temperature compensated. In addition, temperature strongly influenced the amplitude of the circadian transcriptional rhythms during the free-run period in LL, which may confer temperature compensation. We also discuss the possibility that daily changes in forager body temperatures may act as an internal Zeitgeber by fluctuating hive temperature.